Adaptive Heterogeneous Client Sampling for Federated Learning over Wireless Networks Authors Bing Luo, Wenli Xiao, Shiqiang Wang, Jianwei Huang, Leandros Tassiulas Published: 04.22.2024 Updated: 04.22.2024 Summary Federated learning (FL) algorithms usually sample a fraction of clients in each round (partial participation) when the number of participants is large and the server’s communication bandwidth is limited. Recent works on the convergence analysis of FL have focused on unbiased client sampling, e.g., sampling uniformly at random, which suffers from slow wall-clock time for convergence due to high degrees of system heterogeneity and statistical heterogeneity. This paper aims to design an adaptive client sampling algorithm for FL over wireless networks that tackles both system and statistical heterogeneity to minimize the wall-clock convergence time. We obtain a new tractable convergence bound for FL algorithms with arbitrary client sampling probability. Based on the bound, we analytically establish the relationship between the total learning time and sampling probability with an adaptive bandwidth allocation scheme, which results in a non-convex optimization problem. We design an efficient algorithm for learning the unknown parameters in the convergence bound and develop a low-complexity algorithm to approximately solve the non-convex problem. Our solution reveals the impact of system and statistical heterogeneity parameters on the optimal client sampling design. Moreover, our solution shows that as the number of sampled clients increases, the total convergence time first decreases and then increases because a larger sampling number reduces the number of rounds for convergence but results in a longer expected time per-round due to limited wireless bandwidth. Experimental results from both hardware prototype and simulation demonstrate that our proposed sampling scheme significantly reduces the convergence time compared to several baseline sampling schemes. Source arXiv: 2404.13804v1
Wavelength-accurate and wafer-scale process for nonlinear frequency mixers in thin-film lithium niobate Authors C. J. Xin, Shengyuan Lu, Jiayu Yang, Amirhassan Shams-Ansari, Boris Desiatov, Letícia S. Magalhães, Soumya S. Ghosh, Erin McGee, Dylan Renaud, Nicholas Achuthan, Arseniy Zvyagintsev, David Barton III, Neil Sinclair, Marko Lončar Published: 04.18.2024 Updated: 04.18.2024 Summary Recent advancements in thin-film lithium niobate (TFLN) photonics have led to a new generation of high-performance electro-optic devices, including modulators, frequency combs, and microwave-to-optical transducers. However, the broader adoption of TFLN-based devices that rely on all-optical nonlinearities have been limited by the sensitivity of quasi-phase matching (QPM), realized via ferroelectric poling, to fabrication tolerances. Here, we propose a scalable fabrication process aimed at improving the wavelength-accuracy of optical frequency mixers in TFLN. In contrast to the conventional pole-before-etch approach, we first define the waveguide in TFLN and then perform ferroelectric poling. This sequence allows for precise metrology before and after waveguide definition to fully capture the geometry imperfections. Systematic errors can also be calibrated by measuring a subset of devices to fine-tune the QPM design for remaining devices on the wafer. Using this method, we fabricated a large number of second harmonic generation devices aimed at generating 737 nm light, with 73% operating within 5 nm of the target wavelength. Furthermore, we also demonstrate thermo-optic tuning and trimming of the devices via cladding deposition, with the former bringing ~96% of tested devices to the target wavelength. Our technique enables the rapid growth of integrated quantum frequency converters, photon pair sources, and optical parametric amplifiers, thus facilitating the integration of TFLN-based nonlinear frequency mixers into more complex and functional photonic systems. Source arXiv: 2404.12381v1
Tailoring Fault-Tolerance to Quantum Algorithms Authors Zhuangzhuang Chen, Narayanan Rengaswamy Published: 04.18.2024 Updated: 04.18.2024 Summary The standard approach to universal fault-tolerant quantum computing is to develop a general purpose quantum error correction mechanism that can implement a universal set of logical gates fault-tolerantly. Given such a scheme, any quantum algorithm can be realized fault-tolerantly by composing the relevant logical gates from this set. However, we know that quantum computers provide a significant quantum advantage only for specific quantum algorithms. Hence, a universal quantum computer can likely gain from compiling such specific algorithms using tailored quantum error correction schemes. In this work, we take the first steps towards such algorithm-tailored quantum fault-tolerance. We consider Trotter circuits in quantum simulation, which is an important application of quantum computing. We develop a solve-and-stitch algorithm to systematically synthesize physical realizations of Clifford Trotter circuits on the well-known $[![ n,n-2,2 ]!]$ error-detecting code family. Our analysis shows that this family implements Trotter circuits with optimal depth, thereby serving as an illuminating example of tailored quantum error correction. We achieve fault-tolerance for these circuits using flag gadgets, which add minimal overhead. The solve-and-stitch algorithm has the potential to scale beyond this specific example and hence provide a principled approach to tailored fault-tolerance in quantum computing. Source arXiv: 2404.11953v1
Entanglement-assisted quantum transduction Authors Haowei Shi, Quntao Zhuang Published: 04.15.2024 Updated: 04.15.2024 Summary A quantum transducer converts an input signal to an output at a different frequency, while maintaining the quantum information with high fidelity. When operating between the microwave and optical frequencies, it is crucial for quantum networking between quantum computers via low-loss optical links, and thereby enabling distributed quantum computing. However, the state-of-the-art quantum transducers suffer from low transduction efficiency due to weak nonlinear coupling, wherein increasing pump power to enhance efficiency leads to inevitable thermal noise from heating. Moreover, we reveal that the efficiency-bandwidth product in such systems is fundamentally limited by pump power and nonlinear coupling coefficient, irrespective of cavity engineering efforts. To resolve the conundrum, we propose to boost the transduction efficiency by consuming entanglement within the same frequency band (e.g., microwave-microwave or optical-optical entanglement). Via a squeezer-coupler-antisqueezer sandwich structure, the protocol enhances the transduction efficiency to unity in the ideal lossless case, given an arbitrarily weak nonlinear coupling, which establishes a high-fidelity quantum communication link without any signal encoding. In practical cavity systems, our entanglement-assisted protocol surpasses the non-assisted fundamental limit of the efficiency-bandwidth product and reduces the threshold cooperativity for positive quantum capacity by a factor proportional to two-mode squeezing gain. Given a fixed cooperativity, our approach increases the broadband quantum capacity by orders of magnitude. Source arXiv: 2404.09441v1
Lower bounds on bipartite entanglement in noisy graph states Authors Aqil Sajjad, Eneet Kaur, Kenneth Goodenough, Don Towsley, Saikat Guha Published: 04.13.2024 Updated: 04.13.2024 Summary Graph states are a key resource for a number of applications in quantum information theory. Due to the inherent noise in noisy intermediate-scale quantum (NISQ) era devices, it is important to understand the effects noise has on the usefulness of graph states. We consider a noise model where the initial qubits undergo depolarizing noise before the application of the CZ operations that generate edges between qubits situated at the nodes of the resulting graph state. For this model we develop a method for calculating the coherent information — a lower bound on the rate at which entanglement can be distilled, across a bipartition of the graph state. We also identify some patterns on how adding more nodes or edges affects the bipartite distillable entanglement. As an application, we find a family of graph states that maintain a strictly positive coherent information for any amount of (non-maximal) depolarizing noise. Source arXiv: 2404.09014v1
On noise in swap ASAP repeater chains: exact analytics, distributions and tight approximations Authors Kenneth Goodenough, Tim Coopmans, Don Towsley Published: 04.10.2024 Updated: 04.10.2024 Summary Losses are one of the main bottlenecks for the distribution of entanglement in quantum networks, which can be overcome by the implementation of quantum repeaters. The most basic form of a quantum repeater chain is the swap ASAP repeater chain. In such a repeater chain, elementary links are probabilistically generated and deterministically swapped as soon as two adjacent links have been generated. As each entangled state is waiting to be swapped, decoherence is experienced, turning the fidelity of the entangled state between the end nodes of the chain into a random variable. Fully characterizing the (average) fidelity as the repeater chain grows is still an open problem. Here, we analytically investigate the case of equally-spaced repeaters, where we find exact analytic formulae for all moments of the fidelity up to 25 segments. We obtain these formulae by providing a general solution in terms of a generating function; a function whose n’th term in its Maclaurin series yields the moments of the fidelity for n segments. We generalize this approaches as well to a global cut-off policy — a method for increasing fidelity at the cost of longer entanglement delivery times — allowing for fast optimization of the cut-off parameter by eliminating the need for Monte Carlo simulation. We furthermore find simple approximations of the average fidelity that are exponentially tight, and, for up to 10 segments, the full distribution of the delivered fidelity. We use this to analytically calculate the secret-key rate when the distributed entanglement is used for quantum-key distribution, both with and without binning methods. In follow-up work we exploit a connection to a model in statistical physics to numerically calculate quantities of interest for the inhomogeneous multipartite case. Source arXiv: 2404.07146v1
Integrated electro-optics on thin-film lithium niobate Authors Yaowen Hu, Di Zhu, Shengyuan Lu, Xinrui Zhu, Yunxiang Song, Dylan Renaud, Daniel Assumpcao, Rebecca Cheng, CJ Xin, Matthew Yeh, Hana Warner, Xiangwen Guo, Amirhassan Shams-Ansari, David Barton, Neil Sinclair, Marko Loncar Published: 04.09.2024 Updated: 04.11.2024 Summary Electro-optics serves as the crucial bridge between electronics and photonics, unlocking a wide array of applications ranging from communications and computing to sensing and quantum information. Integrated electro-optics approaches in particular enable essential electronic high-speed control for photonics while offering substantial photonic parallelism for electronics. Recent strides in thin-film lithium niobate photonics have ushered revolutionary advancements in electro-optics. This technology not only offers the requisite strong electro-optic coupling but also boasts ultra-low optical loss and high microwave bandwidth. Further, its tight confinement and compatibility with nanofabrication allow for unprecedented reconfigurability and scalability, facilitating the creation of novel and intricate devices and systems that were once deemed nearly impossible in bulk systems. Building upon this platform, the field has witnessed the emergence of various groundbreaking electro-optic devices surpassing the current state of the art, and introducing functionalities that were previously non-existent. This technological leap forward provides a unique framework to explore various realms of physics as well, including photonic non-Hermitian synthetic dimensions, active topological physics, and quantum electro-optics. In this review, we present the fundamental principles of electro-optics, drawing connections between fundamental science and the forefront of technology. We discuss the accomplishments and future prospects of integrated electro-optics, enabled by thin-film lithium niobate platform. Source arXiv: 2404.06398v2
From Similarity to Superiority: Channel Clustering for Time Series Forecasting Authors Jialin Chen, Jan Eric Lenssen, Aosong Feng, Weihua Hu, Matthias Fey, Leandros Tassiulas, Jure Leskovec, Rex Ying Published: 03.31.2024 Updated: 03.31.2024 Summary Time series forecasting has attracted significant attention in recent decades. Previous studies have demonstrated that the Channel-Independent (CI) strategy improves forecasting performance by treating different channels individually, while it leads to poor generalization on unseen instances and ignores potentially necessary interactions between channels. Conversely, the Channel-Dependent (CD) strategy mixes all channels with even irrelevant and indiscriminate information, which, however, results in oversmoothing issues and limits forecasting accuracy. There is a lack of channel strategy that effectively balances individual channel treatment for improved forecasting performance without overlooking essential interactions between channels. Motivated by our observation of a correlation between the time series model’s performance boost against channel mixing and the intrinsic similarity on a pair of channels, we developed a novel and adaptable Channel Clustering Module (CCM). CCM dynamically groups channels characterized by intrinsic similarities and leverages cluster identity instead of channel identity, combining the best of CD and CI worlds. Extensive experiments on real-world datasets demonstrate that CCM can (1) boost the performance of CI and CD models by an average margin of 2.4% and 7.2% on long-term and short-term forecasting, respectively; (2) enable zero-shot forecasting with mainstream time series forecasting models; (3) uncover intrinsic time series patterns among channels and improve interpretability of complex time series models. Source arXiv: 2404.01340v1
Efficient Generation of Multi-partite Entanglement between Non-local Superconducting Qubits using Classical Feedback Authors Akel Hashim, Ming Yuan, Pranav Gokhale, Larry Chen, Christian Juenger, Neelay Fruitwala, Yilun Xu, Gang Huang, Liang Jiang, Irfan Siddiqi Published: 03.27.2024 Updated: 03.27.2024 Summary Quantum entanglement is one of the primary features which distinguishes quantum computers from classical computers. In gate-based quantum computing, the creation of entangled states or the distribution of entanglement across a quantum processor often requires circuit depths which grow with the number of entangled qubits. However, in teleportation-based quantum computing, one can deterministically generate entangled states with a circuit depth that is constant in the number of qubits, provided that one has access to an entangled resource state, the ability to perform mid-circuit measurements, and can rapidly transmit classical information. In this work, aided by fast classical FPGA-based control hardware with a feedback latency of only 150 ns, we explore the utility of teleportation-based protocols for generating non-local, multi-partite entanglement between superconducting qubits. First, we demonstrate well-known protocols for generating Greenberger-Horne-Zeilinger (GHZ) states and non-local CNOT gates in constant depth. Next, we utilize both protocols for implementing an unbounded fan-out (i.e., controlled-NOT-NOT) gate in constant depth between three non-local qubits. Finally, we demonstrate deterministic state teleportation and entanglement swapping between qubits on opposite side of our quantum processor. Source arXiv: 2403.18768v1
A Terahertz Bandwidth Nonmagnetic Isolator Authors Haotian Cheng, Yishu Zhou, Freek Ruesink, Margaret Pavlovich, Shai Gertler, Andrew L. Starbuck, Andrew J. Leenheer, Andrew T. Pomerene, Douglas C. Trotter, Christina Dallo, Matthew Boady, Katherine M. Musick, Michael Gehl, Ashok Kodigala, Matt Eichenfield, Anthony L. Lentine, Nils T. Otterstrom, Peter T. Rakich Published: 03.15.2024 Updated: 03.15.2024 Summary Integrated photonics could bring transformative breakthroughs in computing, networking, imaging, sensing, and quantum information processing, enabled by increasingly sophisticated optical functionalities on a photonic chip. However, wideband optical isolators, which are essential for the robust operation of practically all optical systems, have been challenging to realize in integrated form due to the incompatibility of magnetic media with these circuit technologies. Here, we present the first-ever demonstration of an integrated non-magnetic optical isolator with terahertz-level optical bandwidth. The system is comprised of two acousto-optic frequency-shifting beam splitters which create a non-reciprocal multimode interferometer exhibiting high-contrast, nonreciprocal light transmission. We dramatically enhance the isolation bandwidth of this system by precisely dispersion balancing the paths of the interferometer. Using this approach, we demonstrate integrated nonmagnetic isolators with an optical contrast as high as 28 dB, insertion losses as low as -2.16 dB, and optical bandwidths as high as 2 THz (16 nm). We also show that the center frequency and direction of optical isolation are rapidly reconfigurable by tuning the relative phase of the microwave signals used to drive the acousto-optic beam splitters. With their CMOS compatibility, wideband operation, low losses, and rapid reconfigurability, such integrated isolators could address a key barrier to the integration of a wide range of photonic functionalities on a chip. Looking beyond the current demonstration, this bandwidth-scalable approach to nonmagnetic isolation opens the door to ultrawideband (>10 THz) isolators, which are needed to shrink state-of-the-art imaging, sensing, and communications systems into photonic integrated circuits. Source arXiv: 2403.10628v1
Efficient High-Resolution Time Series Classification via Attention Kronecker Decomposition Authors Aosong Feng, Jialin Chen, Juan Garza, Brooklyn Berry, Francisco Salazar, Yifeng Gao, Rex Ying, Leandros Tassiulas Published: 03.07.2024 Updated: 03.07.2024 Summary The high-resolution time series classification problem is essential due to the increasing availability of detailed temporal data in various domains. To tackle this challenge effectively, it is imperative that the state-of-the-art attention model is scalable to accommodate the growing sequence lengths typically encountered in high-resolution time series data, while also demonstrating robustness in handling the inherent noise prevalent in such datasets. To address this, we propose to hierarchically encode the long time series into multiple levels based on the interaction ranges. By capturing relationships at different levels, we can build more robust, expressive, and efficient models that are capable of capturing both short-term fluctuations and long-term trends in the data. We then propose a new time series transformer backbone (KronTime) by introducing Kronecker-decomposed attention to process such multi-level time series, which sequentially calculates attention from the lower level to the upper level. Experiments on four long time series datasets demonstrate superior classification results with improved efficiency compared to baseline methods. Source arXiv: 2403.04882v1
Octave-spanning Kerr soliton microcombs on thin-film lithium niobate Authors Yunxiang Song, Yaowen Hu, Xinrui Zhu, Kiyoul Yang, Marko Loncar Published: 03.02.2024 Updated: 03.02.2024 Summary Dissipative Kerr solitons from optical microresonators, commonly referred to as soliton microcombs, have been developed for a broad range of applications, including precision measurement, optical frequency synthesis, and ultra-stable microwave and millimeter wave generation, all on a chip. An important goal for microcombs is self referencing, which requires octave-spanning bandwidths to detect and stabilize the comb carrier envelope offset frequency. Further, detection and locking of the comb spacings are often achieved using frequency division by electro-optic modulation. The thin-film lithium niobate photonic platform, with its low loss, strong second-order nonlinearity, and large Pockels effect, is ideally suited for these tasks. However, octave-spanning soliton microcombs are challenging to demonstrate on this platform, largely complicated by strong Raman effects hindering reliable fabrication of soliton devices. Here, we demonstrate entirely connected and octave-spanning soliton microcombs on thin-film lithium niobate. With appropriate control over microresonator free spectral range and dissipation spectrum, we show that soliton-inhibiting Raman effects are suppressed, and soliton devices are fabricated with near-unity yield. Our work offers an unambiguous method for soliton generation on strongly Raman-active materials. Further, it anticipates monolithically integrated, self-referenced frequency standards in conjunction with established technologies, such as periodically poled waveguides and electro-optic modulators, on thin-film lithium niobate. Source arXiv: 2403.01107v1
Entanglement-enabled advantage for learning a bosonic random displacement channel Authors Changhun Oh, Senrui Chen, Yat Wong, Sisi Zhou, Hsin-Yuan Huang, Jens A. H. Nielsen, Zheng-Hao Liu, Jonas S. Neergaard-Nielsen, Ulrik L. Andersen, Liang Jiang, John Preskill Published: 02.29.2024 Updated: 02.29.2024 Summary We show that quantum entanglement can provide an exponential advantage in learning properties of a bosonic continuous-variable (CV) system. The task we consider is estimating a probabilistic mixture of displacement operators acting on $n$ bosonic modes, called a random displacement channel. We prove that if the $n$ modes are not entangled with an ancillary quantum memory, then the channel must be sampled a number of times exponential in $n$ in order to estimate its characteristic function to reasonable precision; this lower bound on sample complexity applies even if the channel inputs and measurements performed on channel outputs are chosen adaptively. On the other hand, we present a simple entanglement-assisted scheme that only requires a number of samples independent of $n$, given a sufficient amount of squeezing. This establishes an exponential separation in sample complexity. We then analyze the effect of photon loss and show that the entanglement-assisted scheme is still significantly more efficient than any lossless entanglement-free scheme under mild experimental conditions. Our work illuminates the role of entanglement in learning continuous-variable systems and points toward experimentally feasible demonstrations of provable entanglement-enabled advantage using CV quantum platforms. Source arXiv: 2402.18809v1
Universal Spreading of Conditional Mutual Information in Noisy Random Circuits Authors Su-un Lee, Changhun Oh, Yat Wong, Senrui Chen, Liang Jiang Published: 02.28.2024 Updated: 02.28.2024 Summary We study the evolution of conditional mutual information in generic open quantum systems, focusing on one-dimensional random circuits with interspersed local noise. Unlike in noiseless circuits, where conditional mutual information spreads linearly while being bounded by the lightcone, we find that noisy random circuits with an error rate $p$ exhibit superlinear propagation of conditional mutual information, which diverges far beyond the lightcone at a critical circuit depth $t_c propto p^{-1}$. We demonstrate that the underlying mechanism for such rapid spreading is the combined effect of local noise and a scrambling unitary, which selectively removes short-range correlations while preserving long-range correlations. To analytically capture the dynamics of conditional mutual information in noisy random circuits, we introduce a coarse-graining method, and we validate our theoretical results through numerical simulations. Furthermore, we identify a universal scaling law governing the spreading of conditional mutual information. Source arXiv: 2402.18548v1
A scalable cavity-based spin-photon interface in a photonic integrated circuit Authors Kevin C. Chen, Ian Christen, Hamza Raniwala, Marco Colangelo, Lorenzo De Santis, Katia Shtyrkova, David Starling, Ryan Murphy, Linsen Li, Karl Berggren, P. Benjamin Dixon, Matthew Trusheim, Dirk Englund Published: 02.28.2024 Updated: 02.28.2024 Summary A central challenge in quantum networking is transferring quantum states between different physical modalities, such as between flying photonic qubits and stationary quantum memories. One implementation entails using spin-photon interfaces that combine solid-state spin qubits, such as color centers in diamond, with photonic nanostructures. However, while high-fidelity spin-photon interactions have been demonstrated on isolated devices, building practical quantum repeaters requires scaling to large numbers of interfaces yet to be realized. Here, we demonstrate integration of nanophotonic cavities containing tin-vacancy (SnV) centers in a photonic integrated circuit (PIC). Out of a six-channel quantum micro-chiplet (QMC), we find four coupled SnV-cavity devices with an average Purcell factor of ~7. Based on system analyses and numerical simulations, we find with near-term improvements this multiplexed architecture can enable high-fidelity quantum state transfer, paving the way towards building large-scale quantum repeaters. Source arXiv: 2402.18057v1
Twenty-nine million Intrinsic Q-factor Monolithic Microresonators on Thin Film Lithium Niobate Authors Xinrui Zhu, Yaowen Hu, Shengyuan Lu, Hana K. Warner, Xudong Li, Yunxiang Song, Leticia Magalhaes, Amirhassan Shams-Ansari, Neil Sinclair, Marko Loncar Published: 02.25.2024 Updated: 02.25.2024 Summary The recent emergence of thin-film lithium niobate (TFLN) has extended the landscape of integrated photonics. This has been enabled by the commercialization of TFLN wafers and advanced nanofabrication of TFLN such as high-quality dry etching. However, fabrication imperfections still limit the propagation loss to a few dB/m, restricting the impact of this platform. Here, we demonstrate TFLN microresonators with a record-high intrinsic quality (Q) factor of twenty-nine million, corresponding to an ultra-low propagation loss of 1.3 dB/m. We present spectral analysis and the statistical distribution of Q factors across different resonator geometries. Our work pushes the fabrication limits of TFLN photonics to achieve a Q factor within one order of magnitude of the material limit. Source arXiv: 2402.16161v1
Progressive-Proximity Bit-Flipping for Decoding Surface Codes Authors Michele Pacenti, Mark F. Flanagan, Dimitris Chytas, Bane Vasic Published: 02.24.2024 Updated: 02.24.2024 Summary Topological quantum codes, such as toric and surface codes, are excellent candidates for hardware implementation due to their robustness against errors and their local interactions between qubits. However, decoding these codes efficiently remains a challenge: existing decoders often fall short of meeting requirements such as having low computational complexity (ideally linear in the code’s blocklength), low decoding latency, and low power consumption. In this paper we propose a novel bit-flipping (BF) decoder tailored for toric and surface codes. We introduce the proximity vector as a heuristic metric for flipping bits, and we develop a new subroutine for correcting a particular class of harmful degenerate errors. Our algorithm achieves linear complexity growth and it can be efficiently implemented as it only involves simple operations such as bit-wise additions, quasi-cyclic permutations and vector-matrix multiplications. The proposed decoder shows a decoding threshold of 7.5% for the 2D toric code and 7% for the rotated planar code over the binary symmetric channel. Source arXiv: 2402.15924v1
LNoS: Lithium Niobate on Silicon Spatial Light Modulator Authors Sivan Trajtenberg-Mills, Mohamed ElKabbash, Cole J. Brabec, Christopher L. Panuski, Ian Christen, Dirk Englund Published: 02.22.2024 Updated: 02.22.2024 Summary Programmable spatiotemporal control of light is crucial for advancements in optical communications, imaging, and quantum technologies. Commercial spatial light modulators (SLMs) typically have megapixel-scale apertures but are limited to ~kHz operational speeds. Developing a device that controls a similar number of spatial modes at high speeds could potentially transform fields such as imaging through scattering media, quantum computing with cold atoms and ions, and high-speed machine vision, but to date remains an open challenge. In this work we introduce and demonstrate a free-form, resonant electro-optic (EO) modulator with megapixel apertures using CMOS integration. The optical layer features a Lithium Niobate (LN) thin-film integrated with a photonic crystal (PhC), yielding a guided mode resonance (GMR) with a Q-factor>1000, a field overlap coefficient ~90% and a 1.6 GHz 3-dB modulation bandwidth (detector limited). To realize a free-form and scalable SLM, we fabricate the PhC via interference lithography and develop a procedure to bond the device to a megapixel CMOS backplane. We identify limitations in existing EO materials and CMOS backplanes that must be overcome to simultaneously achieve megapixel-scale, GHz-rate operation. The `LN on Silicon’ (LNoS) architecture we present is a blueprint towards realizing such devices. Source arXiv: 2402.14608v1
Game Design Inspired by Scientific Concepts of Quantum Physics Authors Sunanda Prabhu Gaunkar, Nancy Kawalek, Denise Fischer, Umang Bhatia, Shobhit Verma, Filip Rozpedek, Uri Zvi Published: 02.20.2024 Updated: 02.20.2024 Summary The huge gap between the public perception of science and the reality of scientific research severely limits the scope of public engagement with science. We create and develop new theatre, film and games work and related artistic endeavors inspired by science and technology. In this paper, we describe the Quantum Games Project, one of the most recent artistic endeavors in our lab. This project consists of a series of card and digital games and an immersive experience, all of which expose the public to quantum physics without learning barriers. Quantum physics explains the counter-intuitive and surprising ways matter behaves at the subatomic level. It is an exciting and growing field that offers solutions to new technological problems. However, learning quantum physics requires several prerequisites, such as a foundation in the sciences and mathematics, and is primarily taught at the undergraduate and higher levels. As a result, the concepts may be too elusive and abstract for the general public to learn independently. This difficulty is compounded by the limited availability of easily understandable resources and teaching materials that do not employ scientific jargon and equations. Our work attempts to solve this problem by communicating the concepts of quantum physics in a way that is comprehensible and accessible to the general public. This paper provides a general overview of the development of the Quantum Games Project, focusing specifically on the Quantum Photo Booth experience, and describes how science is integrated into the very nature of the game development process and its outcome. Source arXiv: 2402.13431v1
Hybrid Kerr-electro-optic frequency combs on thin-film lithium niobate Authors Yunxiang Song, Yaowen Hu, Marko Lončar, Kiyoul Yang Published: 02.18.2024 Updated: 02.18.2024 Summary Optical frequency combs are indispensable links between the optical and microwave domains, enabling a wide range of applications including precision spectroscopy, ultrastable frequency generation, and timekeeping. Chip-scale integration miniaturizes bulk implementations onto photonic chips, offering highly compact, stable, and power-efficient frequency comb sources. State of the art integrated frequency comb sources are based on resonantly-enhanced Kerr effect and, more recently, on electro-optic effect. While the former can routinely reach octave-spanning bandwidths and the latter feature microwave-rate spacings, achieving both in the same material platform has been challenging. Here, we leverage both strong Kerr nonlinearity and efficient electro-optic phase modulation available in the ultralow-loss thin-film lithium niobate photonic platform, to demonstrate a hybrid Kerr-electro-optic frequency comb with stabilized spacing. In our approach, a dissipative Kerr soliton is first generated, and then electro-optic division is used to realize a frequency comb with 2,589 comb lines spaced by 29.308 GHz and spanning 75.9 THz (588 nm) end-to-end. Further, we demonstrate electronic stabilization and control of the soliton spacing, naturally facilitated by our approach. The broadband, microwave-rate comb in this work overcomes the spacing-span tradeoff that exists in all integrated frequency comb sources, and paves the way towards chip-scale solutions for complex tasks such as laser spectroscopy covering multiple bands, micro- and millimeter-wave generation, and massively parallel optical communications. Source arXiv: 2402.11669v1
Slow-Wave Hybrid Magnonics Authors Jing Xu, Changchun Zhong, Shihao Zhuang, Chen Qian, Yu Jiang, Amin Pishehvar, Xu Han, Dafei Jin, Josep M. Jornet, Bo Zhen, Jiamian Hu, Liang Jiang, Xufeng Zhang Published: 02.14.2024 Updated: 02.14.2024 Summary Cavity magnonics is an emerging research area focusing on the coupling between magnons and photons. Despite its great potential for coherent information processing, it has been long restricted by the narrow interaction bandwidth. In this work, we theoretically propose and experimentally demonstrate a novel approach to achieve broadband photon-magnon coupling by adopting slow waves on engineered microwave waveguides. To the best of our knowledge, this is the first time that slow wave is combined with hybrid magnonics. Its unique properties promise great potentials for both fundamental research and practical applications, for instance, by deepening our understanding of the light-matter interaction in the slow wave regime and providing high-efficiency spin wave transducers. The device concept can be extended to other systems such as optomagnonics and magnomechanics, opening up new directions for hybrid magnonics. Source arXiv: 2402.08872v1
Safeguarding Oscillators and Qudits with Distributed Two-Mode Squeezing Authors Anthony J. Brady, Jing Wu, Quntao Zhuang Published: 02.08.2024 Updated: 02.08.2024 Summary Recent advancements in multimode Gottesman-Kitaev-Preskill (GKP) codes have shown great promise in enhancing the protection of both discrete and analog quantum information. This broadened range of protection brings opportunities beyond quantum computing to benefit quantum sensing by safeguarding squeezing — the essential resource in many quantum metrology protocols. However, it is less explored how quantum sensing can benefit quantum error correction. In this work, we provide a unique example where techniques from quantum sensing can be applied to improve multimode GKP codes. Inspired by distributed quantum sensing, we propose the distributed two-mode squeezing (dtms) GKP codes that offer benefits in error correction with minimal active encoding operations. In fact, the proposed codes rely on a single (active) two-mode squeezing element and an array of beamsplitters that effectively distributes continuous-variable correlations to many GKP ancillae, similar to continuous-variable distributed quantum sensing. Despite this simple construction, the code distance achievable with dtms-GKP qubit codes is comparable to previous results obtained through brute-force numerical search [PRX Quantum 4, 040334 (2023)]. Moreover, these codes enable analog noise suppression beyond that of the best-known two-mode codes [Phys. Rev. Lett. 125, 080503 (2020)] without requiring an additional squeezer. We also provide a simple two-stage decoder for the proposed codes, which appears near-optimal for the case of two modes and permits analytical evaluation. Source arXiv: 2402.05888v1
High-Q Cavity Interface for Color Centers in Thin Film Diamond Authors Sophie W. Ding, Michael Haas, Xinghan Guo, Kazuhiro Kuruma, Chang Jin, Zixi Li, David D. Awschalom, Nazar Delegan, F. Joseph Heremans, Alex High, Marko Loncar Published: 02.08.2024 Updated: 02.08.2024 Summary Quantum information technology offers the potential to realize unprecedented computational resources via secure channels capable of distributing entanglement between quantum computers. Diamond, as a host to atom-like defects with optically-accessible spin qubits, is a leading platform to realize quantum memory nodes needed to extend the reach of quantum links. Photonic crystal (PhC) cavities enhance light-matter interaction and are essential ingredients of an efficient interface between spins and photons that are used to store and communicate quantum information respectively. Despite great effort, however, the realization of visible PhC cavities with high quality factor (Q) and design flexibility is challenging in diamond. Here, we demonstrate one- and two-dimensional PhC cavities fabricated in recently developed thin-film diamonds, featuring Q-factors of 1.8×10$^5$ and 1.6×10$^5$, respectively, the highest Qs for visible PhC cavities realized in any material. Importantly, our fabrication process is simple and high-yield, based on conventional planar fabrication techniques, in contrast to previous approaches that rely on complex undercut methods. We also demonstrate fiber-coupled 1D PhC cavities with high photon extraction efficiency, and optical coupling between a single SiV center and such a cavity at 4K achieving a Purcell factor of 13. The demonstrated diamond thin-film photonic platform will improve the performance and scalability of quantum nodes and expand the range of quantum technologies. Source arXiv: 2402.05811v1
Gaussian Boson Sampling to Accelerate NP-Complete Vertex-Minor Graph Classification Authors Mushkan Sureka, Saikat Guha Published: 02.05.2024 Updated: 02.05.2024 Summary Gaussian Boson Sampling (GBS) generate random samples of photon-click patterns from a class of probability distributions that are hard for a classical computer to sample from. Despite heroic demonstrations for quantum supremacy using GBS, Boson Sampling, and instantaneous quantum polynomial (IQP) algorithms, systematic evaluations of the power of these quantum-enhanced random samples when applied to provably hard problems, and performance comparisons with best-known classical algorithms have been lacking. We propose a hybrid quantum-classical algorithm using the GBS for the NP-complete problem of determining if two graphs are vertex minor of one another. The graphs are encoded in GBS and the generated random samples serve as feature vectors in the support vector machine (SVM) classifier. We find a graph embedding that allows trading between the one-shot classification accuracy and the amount of input squeezing, a hard-to-produce quantum resource, followed by repeated trials and majority vote to reach an overall desired accuracy. We introduce a new classical algorithm based on graph spectra, which we show outperforms various well-known graph-similarity algorithms. We compare the performance of our algorithm with this classical algorithm and analyze their time vs problem-size scaling, to yield a desired classification accuracy. Our simulation suggests that with a near-term realizable GBS device- $5$ dB pulsed squeezer, $12$-mode unitary, and reasonable assumptions on coupling efficiency, on-chip losses and detection efficiency of photon number resolving detectors-we can solve a $12$-node vertex minor instances with about $10^3$ fold lower time compared to a powerful desktop computer. Source arXiv: 2402.03524v1
Nanophotonic Phased Array XY Hamiltonian Solver Authors Michelle Chalupnik, Anshuman Singh, James Leatham, Marko Loncar, Moe Soltani Published: 02.02.2024 Updated: 02.02.2024 Summary Solving large-scale computationally hard optimization problems using existing computers has hit a bottleneck. A promising alternative approach uses physics-based phenomena to naturally solve optimization problems wherein the physical phenomena evolves to its minimum energy. In this regard, photonics devices have shown promise as alternative optimization architectures, benefiting from high-speed, high-bandwidth and parallelism in the optical domain. Among photonic devices, programmable spatial light modulators (SLMs) have shown promise in solving large scale Ising model problems to which many computationally hard problems can be mapped. Despite much progress, existing SLMs for solving the Ising model and similar problems suffer from slow update rates and physical bulkiness. Here, we show that using a compact silicon photonic integrated circuit optical phased array (PIC-OPA) we can simulate an XY Hamiltonian, a generalized form of Ising Hamiltonian, where spins can vary continuously. In this nanophotonic XY Hamiltonian solver, the spins are implemented using analog phase shifters in the optical phased array. The far field intensity pattern of the PIC-OPA represents an all-to-all coupled XY Hamiltonian energy and can be optimized with the tunable phase-shifters allowing us to solve an all-to-all coupled XY model. Our results show the utility of PIC-OPAs as compact, low power, and high-speed solvers for nondeterministic polynomial (NP)-hard problems. The scalability of the silicon PIC-OPA and its compatibility with monolithic integration with CMOS electronics further promises the realization of a powerful hybrid photonic/electronic non-Von Neumann compute engine. Source arXiv: 2402.01153v1
Nanophotonic Phased Array XY Hamiltonian Solver Authors Michelle Chalupnik, Anshuman Singh, James Leatham, Marko Loncar, Moe Soltani Published: 02.02.2024 Updated: 03.10.2024 Summary Solving large-scale computationally hard optimization problems using existing computers has hit a bottleneck. A promising alternative approach uses physics-based phenomena to naturally solve optimization problems wherein the physical phenomena evolves to its minimum energy. In this regard, photonics devices have shown promise as alternative optimization architectures, benefiting from high-speed, high-bandwidth and parallelism in the optical domain. Among photonic devices, programmable spatial light modulators (SLMs) have shown promise in solving large scale Ising model problems to which many computationally hard problems can be mapped. Despite much progress, existing SLMs for solving the Ising model and similar problems suffer from slow update rates and physical bulkiness. Here, we show that using a compact silicon photonic integrated circuit optical phased array (PIC-OPA) we can simulate an XY Hamiltonian, a generalized form of Ising Hamiltonian, where spins can vary continuously. In this nanophotonic XY Hamiltonian solver, the spins are implemented using analog phase shifters in the optical phased array. The far field intensity pattern of the PIC-OPA represents an all-to-all coupled XY Hamiltonian energy and can be optimized with the tunable phase-shifters allowing us to solve an all-to-all coupled XY model. Our results show the utility of PIC-OPAs as compact, low power, and high-speed solvers for nondeterministic polynomial (NP)-hard problems. The scalability of the silicon PIC-OPA and its compatibility with monolithic integration with CMOS electronics further promises the realization of a powerful hybrid photonic/electronic non-Von Neumann compute engine. Source arXiv: 2402.01153v2
Resource-efficient and loss-aware photonic graph state preparation using an array of quantum emitters, and application to all-photonic quantum repeaters Authors Eneet Kaur, Ashlesha Patil, Saikat Guha Published: 02.01.2024 Updated: 02.01.2024 Summary Multi-qubit photonic graph states are necessary for quantum communication and computation. Preparing photonic graph states using probabilistic stitching of single photons using linear optics results in a formidable resource requirement due to the need of multiplexing. Quantum emitters present a viable solution to prepare photonic graph states, as they enable controlled production of photons entangled with the emitter qubit, and deterministic two-qubit interactions among emitters. A handful of emitters often suffice to generate useful photonic graph states that would otherwise require millions of single photon sources using the linear-optics method. But, photon loss poses an impediment to this method due to the large depth, i.e., age of the oldest photon, of the graph state, given the typically large number of slow and noisy two-qubit CNOT gates required on emitters. We propose an algorithm that can trade the number of emitters with the graph-state depth, while minimizing the number of emitter CNOTs. We apply our algorithm to generating a repeater graph state (RGS) for all-photonic repeaters. We find that our scheme achieves a far superior rate-vs.-distance performance than using the least number of emitters needed to generate the RGS. Yet, our scheme is able to get the same performance as the linear-optics method of generating the RGS where each emitter is used as a single-photon source, but with orders of magnitude fewer emitters. Source arXiv: 2402.00731v1
Limitations in design and applications of ultra-small mode volume photonic crystals Authors Rubaiya Emran, Michelle Chalupnik, Erik N. Knall, Ralf Riedinger, Cleaven Chia, Marko Loncar Published: 02.01.2024 Updated: 04.16.2024 Summary Ultra-small mode volume nanophotonic crystal cavities have been proposed as powerful tools for increasing coupling rates in cavity quantum electrodynamics systems. However, their adoption in quantum information applications remains elusive. In this work, we investigate possible reasons why, and analyze the impact of different low mode volume resonator design choices on their utility in quantum optics experiments. We analyze band structure features and loss rates of low mode volume bowtie cavities in diamond and demonstrate independent design control over cavity-emitter coupling strength and loss rates. Further, using silicon vacancy centers in diamond as exemplary emitters, we investigate the influence of placement imprecision. We find that the benefit on photon collection efficiency and indistinguishability is limited, while the fabrication complexity of ultra-small cavity designs increases substantially compared to conventional photonic crystals. We conclude that ultra-small mode volume designs are primarily of interest for dispersive spin-photon interactions, which are of great interest for future quantum networks. Source arXiv: 2402.00363v2
Ab-Initio Calculations of Nonlinear Susceptibility and Multi-Phonon Mixing Processes in a 2DEG-Piezoelectric Heterostructure Authors Eric Chatterjee, Alexander Wendt, Daniel Soh, Matt Eichenfield Published: 02.01.2024 Updated: 04.13.2024 Summary Solid-state elastic-wave phonons are a promising platform for a wide range of quantum information applications. An outstanding challenge and enabling capability in harnessing phonons for quantum information processing is achieving strong nonlinear interactions between them. To this end, we propose a general architecture using piezoelectric-semiconductor heterostructures consisting of a piezoelectric acoustic material hosting phonon modes in direct proximity to a two-dimensional electron gas (2DEG). Each phonon in the piezoelectric material carries an electric field, which extends into the 2DEG. The fields induce polarization of 2DEG electrons, which in turn interact with other piezoelectric phononic electric fields. The net result is coupling between the various phonon modes. We derive, from first principles, the nonlinear phononic susceptibility of the system. We show that many nonlinear processes are strongly favored at high electron mobility, motivating the use of the 2DEG to mediate the nonlinearities. We derive in detail the first, second, and third-order susceptibilities and calculate them for the case of a lithium niobate surface acoustic wave interacting with a GaAs-AlGaAs heterostructure 2DEG. We show that, for this system, the strong third-order nonlinearity could enable single-phonon Kerr shift in an acoustic cavity that exceeds realistic cavity linewidths, potentially leading to a new class of acoustic qubit. We further show that the strong second-order nonlinearity could be used to produce a high-gain, traveling-wave parametric amplifier to amplify–and ultimately detect–the outputs of the acoustic cavity qubits. Assuming favorable losses in such a system, these capabilities, combined with the ability to efficiently transduce phonons from microwave electromagnetic fields in transmission lines, thus hold promise for creating all-acoustic quantum information processors. Source arXiv: 2402.00303v2
Optimum classical beam position sensing Authors Wenhua He, Christos N. Gagatsos, Dalziel J. Wilson, Saikat Guha Published: 02.01.2024 Updated: 02.01.2024 Summary Beam displacement measurements are widely used in optical sensing and communications; however, their performance is affected by numerous intrinsic and extrinsic factors including beam profile, propagation loss, and receiver architecture. Here we present a framework for designing a classically optimal beam displacement transceiver, using quantum estimation theory. We consider the canonical task of estimating the position of a diffraction-limited laser beam after passing through an apertured volume characterized by Fresnel-number product DF. As a rule of thumb, higher-order Gaussian modes provide more information about beam displacement, but are more sensitive to loss. Applying quantum Fisher information, we design mode combinations that optimally leverage this trade-off, and show that a greater than 10-fold improvement in precision is possible, relative to the fundamental mode, for a practically relevant DF = 100. We also show that this improvement is realizable with a variety of practical receiver architectures. Our findings extend previous works on lossless transceivers, may have immediate impact on applications such as atomic force microscopy and near-field optical communication, and pave the way towards globally optimal transceivers using non-classical laser fields. Source arXiv: 2402.00259v1
Hypermultiplexed Integrated Tensor Optical Processor Authors Shaoyuan Ou, Alexander Sludds, Ryan Hamerly, Ke Zhang, Hanke Feng, Eric Zhong, Cheng Wang, Dirk Englund, Mengjie Yu, Zaijun Chen Published: 01.31.2024 Updated: 02.11.2024 Summary Optical processors hold great potential to accelerate deep learning tasks with their high clock-rates and low-loss data transmission. However, existing integrated systems are hindered by low scalability due to the quadratic scaling of device counts, energy costs with high-speed analog-to-digital converters, and lack of inline nonlinearity. Here, we overcome these challenges with a wavelength-space-time multiplexed optical tensor processor. Hyperdimensional parallelism allows matrix-matrix multiplications ($N^{3}$ operations) using $O(N)$ devices. We incorporated wavelength-multiplexed III/V-based micron-scale lasers (spanning ~1 THz) for input activation with inline rectifier (ReLU) nonlinearities and thin-film Lithium-Niobate electro-optic modulators ($V_{pi}approx1.3 V$) for dynamic weighting. With each device encoding 10-billion activations per second, we demonstrated a machine-learning model with 405,000 parameters. High-clock-rate (10 GS/s), low-energy (500 fJ/OP) parallel computing with real-time programmability unlocks the full potential of light for next-generation scalable AI accelerators. Source arXiv: 2401.18050v2
Passive environment-assisted quantum transduction with GKP states Authors Zhaoyou Wang, Liang Jiang Published: 01.30.2024 Updated: 01.30.2024 Summary Quantum transducers convert quantum signals from one carrier to another through hybrid interfaces of physical systems. For a quantum transducer between two bosonic modes, direct quantum transduction without shared entanglement or classical communication typically requires a conversion efficiency exceeding 0.5 which is challenging for current experiments. We propose the passive environment-assisted quantum transduction to overcome this stringent requirement. Without internal losses, the quantum transducer realizes a beam splitter unitary between two modes. The added noises to the transduction process from mode 1 to mode 2 is determined by the initial state of mode 2, which can be engineered to enhance the transduction performance. We find that by choosing the ideal Gottesman-Kitaev-Preskill (GKP) states as the initial states of both modes, perfect quantum transduction can be achieved at arbitrarily low conversion efficiencies. In practice, it is crucial to also consider the finite energy constraints and high fidelity quantum transduction remains achievable with GKP states at the few-photon level. Source arXiv: 2401.16781v1
Integrated resonant electro-optic comb enabled by platform-agnostic laser integration Authors Isaac Luntadila Lufungula, Amirhassan Shams-Ansari, Dylan Renaud, Camiel Op de Beeck, Stijn Cuyvers, Stijn Poelman, Maximilien Billet, Gunther Roelkens, Marko Loncar, Bart Kuyken Published: 01.29.2024 Updated: 02.08.2024 Summary The field of integrated photonics has significantly impacted numerous fields including communication, sensing, and quantum physics owing to the efficiency, speed, and compactness of its devices. However, the reliance on off-chip bulk lasers compromises the compact nature of these systems. While silicon photonics and III-V platforms have established integrated laser technologies, emerging demands for ultra-low optical loss, wider bandgaps, and optical nonlinearities necessitate other platforms. Developing integrated lasers on less mature platforms is arduous and costly due to limited throughput or unconventional process requirements. In response, we propose a novel platform-agnostic laser integration technique utilizing a singular design and process flow, applicable without modification to a diverse range of platforms. Leveraging a two-step micro-transfer printing method, we achieve nearly identical laser performance across platforms with refractive indices between 1.7 and 2.5. Experimental validation demonstrates strikingly similar laser characteristics between devices processed on lithium niobate and silicon nitride platforms. Furthermore, we showcase the integration of a laser with a resonant electro-optic comb generator on the thin-film lithium niobate platform, producing over 80 comb lines spanning 12 nm. This versatile technique transcends platform-specific limitations, facilitating applications like microwave photonics, handheld spectrometers, and cost-effective Lidar systems, across multiple platforms. Source arXiv: 2401.16242v2
Cyber-Twin: Digital Twin-boosted Autonomous Attack Detection for Vehicular Ad-Hoc Networks Authors Yagmur Yigit, Ioannis Panitsas, Leandros Maglaras, Leandros Tassiulas, Berk Canberk Published: 01.25.2024 Updated: 01.25.2024 Summary The rapid evolution of Vehicular Ad-hoc NETworks (VANETs) has ushered in a transformative era for intelligent transportation systems (ITS), significantly enhancing road safety and vehicular communication. However, the intricate and dynamic nature of VANETs presents formidable challenges, particularly in vehicle-to-infrastructure (V2I) communications. Roadside Units (RSUs), integral components of VANETs, are increasingly susceptible to cyberattacks, such as jamming and distributed denial-of-service (DDoS) attacks. These vulnerabilities pose grave risks to road safety, potentially leading to traffic congestion and vehicle malfunctions. Current approaches often struggle to effectively merge digital twin technology with Artificial Intelligence (AI) models to boost security and sustainability. Our study introduces an innovative cyber-twin framework tailored to enhance the security of RSUs in VANETs. This framework uniquely combines digital twin technology with cutting-edge AI to offer a real-time, dynamic representation of RSUs. This allows for detailed monitoring and efficient detection of threats, significantly strengthening RSU security in VANETs. Moreover, our framework makes a notable contribution to eco-friendly communication by improving the computational efficiency of RSUs, leading to increased energy efficiency and extended hardware durability. Our results show a considerable enhancement in resource management and attack detection, surpassing the performance of existing solutions. In particular, the cyber-twin framework showed a substantial reduction in RSU load and an optimal balance between resource consumption and high attack detection efficiency, with a defined twinning rate range of seventy-six to ninety per cent. These advancements underscore our commitment to developing sustainable, secure, and resilient vehicular communication systems for the future of smart cities. Source arXiv: 2401.14005v1
Cyber-Twin: Digital Twin-boosted Autonomous Attack Detection for Vehicular Ad-Hoc Networks Authors Yagmur Yigit, Ioannis Panitsas, Leandros Maglaras, Leandros Tassiulas, Berk Canberk Published: 01.25.2024 Updated: 02.03.2024 Summary The rapid evolution of Vehicular Ad-hoc NETworks (VANETs) has ushered in a transformative era for intelligent transportation systems (ITS), significantly enhancing road safety and vehicular communication. However, the intricate and dynamic nature of VANETs presents formidable challenges, particularly in vehicle-to-infrastructure (V2I) communications. Roadside Units (RSUs), integral components of VANETs, are increasingly susceptible to cyberattacks, such as jamming and distributed denial-of-service (DDoS) attacks. These vulnerabilities pose grave risks to road safety, potentially leading to traffic congestion and vehicle malfunctions. Current approaches often struggle to effectively merge digital twin technology with Artificial Intelligence (AI) models to boost security and sustainability. Our study introduces an innovative cyber-twin framework tailored to enhance the security of RSUs in VANETs. This framework uniquely combines digital twin technology with cutting-edge AI to offer a real-time, dynamic representation of RSUs. This allows for detailed monitoring and efficient detection of threats, significantly strengthening RSU security in VANETs. Moreover, our framework makes a notable contribution to eco-friendly communication by improving the computational efficiency of RSUs, leading to increased energy efficiency and extended hardware durability. Our results show a considerable enhancement in resource management and attack detection, surpassing the performance of existing solutions. In particular, the cyber-twin framework showed a substantial reduction in RSU load and an optimal balance between resource consumption and high attack detection efficiency, with a defined twinning rate range of seventy-six to ninety per cent. These advancements underscore our commitment to developing sustainable, secure, and resilient vehicular communication systems for the future of smart cities. Source arXiv: 2401.14005v2
Parameter extraction for a superconducting thermal switch (hTron) SPICE model Authors Valentin Karam, Owen Medeiros, Tareq El Dandachi, Matteo Castellani, Reed Foster, Marco Colangelo, Karl Berggren Published: 01.22.2024 Updated: 01.22.2024 Summary Efficiently simulating large circuits is crucial for the broader use of superconducting nanowire-based electronics. However, current simulation tools for this technology are not adapted to the scaling of circuit size and complexity. We focus on the multilayered heater-nanocryotron (hTron), a promising superconducting nanowire-based switch used in applications such as superconducting nanowire single-photon detector (SNSPD) readout. Previously, the hTron was modeled using traditional finite-element methods (FEM), which fall short in simulating systems at a larger scale. An empirical-based method would be better adapted to this task, enhancing both simulation speed and agreement with experimental data. In this work, we perform switching current and activation delay measurements on 17 hTron devices. We then develop a method for extracting physical fitting parameters used to characterize the devices. We build a SPICE behavioral model that reproduces the static and transient device behavior using these parameters, and validate it by comparing its performance to the model developed in a prior work, showing an improvement in simulation time by several orders of magnitude. Our model provides circuit designers with a tool to help understand the hTron’s behavior during all design stages, thus promoting broader use of the hTron across various new areas of application. Source arXiv: 2401.12360v1
Constrained Reinforcement Learning for Adaptive Controller Synchronization in Distributed SDN Authors Ioannis Panitsas, Akrit Mudvari, Leandros Tassiulas Published: 01.21.2024 Updated: 01.21.2024 Summary In software-defined networking (SDN), the implementation of distributed SDN controllers, with each controller responsible for managing a specific sub-network or domain, plays a critical role in achieving a balance between centralized control, scalability, reliability, and network efficiency. These controllers must be synchronized to maintain a logically centralized view of the entire network. While there are various approaches for synchronizing distributed SDN controllers, most tend to prioritize goals such as optimization of communication latency or load balancing, often neglecting to address both the aspects simultaneously. This limitation becomes particularly significant when considering applications like Augmented and Virtual Reality (AR/VR), which demand constrained network latencies and substantial computational resources. Additionally, many existing studies in this field predominantly rely on value-based reinforcement learning (RL) methods, overlooking the potential advantages offered by state-of-the-art policy-based RL algorithms. To bridge this gap, our work focuses on examining deep reinforcement learning (DRL) techniques, encompassing both value-based and policy-based methods, to guarantee an upper latency threshold for AR/VR task offloading within SDN environments, while selecting the most cost-effective servers for AR/VR task offloading. Our evaluation results indicate that while value-based methods excel in optimizing individual network metrics such as latency or load balancing, policy-based approaches exhibit greater robustness in adapting to sudden network changes or reconfiguration. Source arXiv: 2403.08775v1
Reconfigurable Intelligent Surface (RIS)-Assisted Entanglement Distribution in FSO Quantum Networks Authors Mahdi Chehimi, Mohamed Elhattab, Walid Saad, Gayane Vardoyan, Nitish K. Panigrahy, Chadi Assi, Don Towsley Published: 01.19.2024 Updated: 01.19.2024 Summary Quantum networks (QNs) relying on free-space optical (FSO) quantum channels can support quantum applications in environments wherein establishing an optical fiber infrastructure is challenging and costly. However, FSO-based QNs require a clear line-of-sight (LoS) between users, which is challenging due to blockages and natural obstacles. In this paper, a reconfigurable intelligent surface (RIS)-assisted FSO-based QN is proposed as a cost-efficient framework providing a virtual LoS between users for entanglement distribution. A novel modeling of the quantum noise and losses experienced by quantum states over FSO channels defined by atmospheric losses, turbulence, and pointing errors is derived. Then, the joint optimization of entanglement distribution and RIS placement problem is formulated, under heterogeneous entanglement rate and fidelity constraints. This problem is solved using a simulated annealing metaheuristic algorithm. Simulation results show that the proposed framework effectively meets the minimum fidelity requirements of all users’ quantum applications. This is in stark contrast to baseline algorithms that lead to a drop of at least 83% in users’ end-to-end fidelities. The proposed framework also achieves a 64% enhancement in the fairness level between users compared to baseline rate maximizing frameworks. Finally, the weather conditions, e.g., rain, are observed to have a more significant effect than pointing errors and turbulence. Source arXiv: 2401.10823v1
Cavity-enhanced narrowband spectral filters using rare-earth ions doped in thin-film lithium niobate Authors Yuqi Zhao, Dylan Renaud, Demitry Farfurnik, Subhojit Dutta, Neil Sinclair, Marko Loncar, Edo Waks Published: 01.18.2024 Updated: 01.18.2024 Summary On-chip optical filters are fundamental components in optical signal processing. While rare-earth ion-doped crystals offer ultra-narrow optical filtering via spectral hole burning, their applications have primarily been limited to those using bulk crystals, restricting their utility. In this work, we demonstrate cavity-enhanced spectral filtering based on rare-earth ions in an integrated nonlinear optical platform. We incorporate rare-earth ions into high quality-factor ring resonators patterned in thin-film lithium niobate. By spectral hole burning in a critically-coupled resonance mode, we achieve bandpass filters ranging from 7 MHz linewidth, with 13.0 dB of extinction, to 24 MHz linewidth, with 20.4 dB of extinction. These filters outperform those of the highest quality factor ring resonators demonstrated in the thin-film lithium niobate integrated platform. Moreover, the cavity enables reconfigurable filtering by varying the cavity coupling rate. For instance, as opposed to the bandpass filter, we demonstrate a bandstop filter utilizing an under-coupled ring resonator. Such versatile integrated spectral filters with high extinction ratio and narrow linewidth could serve as fundamental components for optical signal processing and optical memories on-a-chip. Source arXiv: 2401.09655v1
Optimistic Entanglement Purification in Quantum Networks Authors Mohammad Mobayenjarihani, Gayane Vardoyan, Don Towsley Published: 01.16.2024 Updated: 01.16.2024 Summary Noise and photon loss encountered on quantum channels pose a major challenge for reliable entanglement generation in quantum networks. In near-term networks, heralding is required to inform endpoints of successfully generated entanglement. If after heralding, entanglement fidelity is too low, entanglement purification can be utilized to probabilistically increase fidelity. Traditionally, purification protocols proceed as follows: generate heralded EPR pairs, execute a series of quantum operations on two or more pairs between two nodes, and classically communicate results to check for success. Purification may require several rounds while qubits are stored in memories, vulnerable to decoherence. In this work, we explore the notion of optimistic purification in a single link setup, wherein classical communication required for heralding and purification is delayed, possibly to the end of the process. Optimism reduces the overall time EPR pairs are stored in memory. While this is beneficial for fidelity, it can result in lower rates due to the continued execution of protocols with sparser heralding and purification outcome updates. We apply optimism to the entanglement pumping scheme, ground- and satellite-based EPR generation sources, and current state-of-the-art purification circuits. We evaluate sensitivity performance to a number of parameters including link length, EPR source rate and fidelity, and memory coherence time. We observe that our optimistic protocols are able to increase fidelity, while the traditional approach becomes detrimental to it for long distances. We study the trade-off between rate and fidelity under entanglement-based QKD, and find that optimistic schemes can yield higher rates compared to non-optimistic counterparts, with most advantages seen in scenarios with low initial fidelity and short coherence times. Source arXiv: 2401.08034v1
All-optical nonlinear activation function based on stimulated Brillouin scattering Authors Grigorii Slinkov, Steven Becker, Dirk Englund, Birgit Stiller Published: 01.10.2024 Updated: 01.10.2024 Summary Photonic neural networks have demonstrated their potential over the past decades, but have not yet reached the full extent of their capabilities. One reason for this lies in an essential component – the nonlinear activation function, which ensures that the neural network can perform the required arbitrary nonlinear transformation. The desired all-optical nonlinear activation function is difficult to realize, and as a result, most of the reported photonic neural networks rely on opto-electronic activation functions. Usually, the sacrifices made are the unique advantages of photonics, such as resource-efficient coherent and frequency-multiplexed information encoding. In addition, opto-electronic activation functions normally limit the photonic neural network depth by adding insertion losses. Here, we experimentally demonstrate an in-fiber photonic nonlinear activation function based on stimulated Brillouin scattering. Our design is coherent and frequency selective, making it suitable for multi-frequency neural networks. The optoacoustic activation function can be tuned continuously and all-optically between a variety of activation functions such as LeakyReLU, Sigmoid, and Quadratic. In addition, our design amplifies the input signal with gain as high as $20,mathrm{dB}$, compensating for insertion losses on the fly, and thus paving the way for deep optical neural networks. Source arXiv: 2401.05135v1
The Near-optimal Performance of Quantum Error Correction Codes Authors Guo Zheng, Wenhao He, Gideon Lee, Liang Jiang Published: 01.04.2024 Updated: 01.04.2024 Summary The Knill-Laflamme (KL) conditions distinguish perfect quantum error correction codes, and it has played a critical role in the discovery of state-of-the-art codes. However, the family of perfect codes is a very restrictive one and does not necessarily contain the best-performing codes. Therefore, it is desirable to develop a generalized and quantitative performance metric. In this Letter, we derive the near-optimal channel fidelity, a concise and optimization-free metric for arbitrary codes and noise. The metric provides a narrow two-sided bound to the optimal code performance, and it can be evaluated with exactly the same input required by the KL conditions. We demonstrate the numerical advantage of the near-optimal channel fidelity through multiple qubit code and oscillator code examples. Compared to conventional optimization-based approaches, the reduced computational cost enables us to simulate systems with previously inaccessible sizes, such as oscillators encoding hundreds of average excitations. Moreover, we analytically derive the near-optimal performance for the thermodynamic code and the Gottesman-Kitaev-Preskill (GKP) code. In particular, the GKP code’s performance under excitation loss improves monotonically with its energy and converges to an asymptotic limit at infinite energy, which is distinct from other oscillator codes. Source arXiv: 2401.02022v1
Fault-tolerant quantum computation by hybrid qubits with bosonic cat-code and single photons Authors Jaehak Lee, Nuri Kang, Seok-Hyung Lee, Hyunseok Jeong, Liang Jiang, Seung-Woo Lee Published: 12.31.2023 Updated: 12.31.2023 Summary Hybridizing different degrees of freedom or physical platforms potentially offers various advantages in building scalable quantum architectures. We here introduce a fault-tolerant hybrid quantum computation by taking the advantages of both discrete variable (DV) and continuous variable (CV) systems. Particularly, we define a CV-DV hybrid qubit with bosonic cat-code and single photon, which is implementable in current photonic platforms. By the cat-code encoded in the CV part, the dominant loss errors are readily correctable without multi-qubit encoding, while the logical basis is inherently orthogonal due to the DV part. We design fault-tolerant architectures by concatenating hybrid qubits and an outer DV quantum error correction code such as topological codes, exploring their potential merits in developing scalable quantum computation. We demonstrate by numerical simulations that our scheme is at least an order of magnitude more resource-efficient over all previous proposals in photonic platforms, allowing to achieve a record-high loss threshold among existing CV and hybrid approaches. We discuss its realization not only in all-photonic platforms but also in other hybrid platforms including superconduting and trapped-ion systems, which allows us to find various efficient routes towards fault-tolerant quantum computing. Source arXiv: 2401.00450v1
Photonic crystal cavity IQ modulators in thin-film lithium niobate for coherent communications Authors Hugo Larocque, Dashiell L. P. Vitullo, Alexander Sludds, Hamed Sattari, Ian Christen, Gregory Choong, Ivan Prieto, Jacopo Leo, Homa Zarebidaki, Sanjaya Lohani, Brian T. Kirby, Öney O. Soykal, Moe Soltani, Amir H. Ghadimi, Dirk Englund, Mikkel Heuck Published: 12.27.2023 Updated: 12.27.2023 Summary Thin-Film Lithium Niobate (TFLN) is an emerging integrated photonic platform showing great promise due to its large second-order nonlinearity at microwave and optical frequencies, cryogenic compatibility, large piezoelectric response, and low optical loss at visible and near-infrared wavelengths. These properties enabled Mach-Zehnder interferometer-based devices to demonstrate amplitude- and in-phase/quadrature (IQ) modulation at voltage levels compatible with complementary metal-oxide-semiconductor (CMOS) electronics. Maintaining low-voltage operation requires centimeter-scale device lengths, making it challenging to realize the large-scale circuits required by ever-increasing bandwidth demands in data communications. Reduced device sizes reaching the 10 um scale are possible with photonic crystal (PhC) cavities. So far, their operation has been limited to modulation of amplitudes and required circulators or lacked cascadability. Here, we demonstrate a compact IQ modulator using two PhC cavities operating as phase shifters in a Fabry-Perot-enhanced Michelson interferometer configuration. It supports cascadable amplitude and phase modulation at GHz bandwidths with CMOS-compatible voltages. While the bandwidth limitation of resonant devices is often considered detrimental, their compactness enables dense co-integration with CMOS electronics where clock-rate-level operation (few GHz) removes power-hungry electrical time-multiplexing. Recent demonstrations of chip-scale transceivers with dense-wavelength division multiplied transceivers could be monolithically implemented and driven toward ultimate information densities using TFLN electro-optic frequency combs and our PhC IQ modulators. Source arXiv: 2312.16746v1
Universal Control in Bosonic Systems with Weak Kerr Nonlinearities Authors Ming Yuan, Alireza Seif, Andrew Lingenfelter, David I. Schuster, Aashish A. Clerk, Liang Jiang Published: 12.25.2023 Updated: 12.25.2023 Summary Resonators with weak single-photon self-Kerr nonlinearities can theoretically be used to prepare Fock states in the presence of a loss much larger than their nonlinearities. Two necessary ingredients are large displacements and a two-photon (parametric) drive. Here, we find that these systems can be controlled to achieve any desired gate operation in a finite dimensional subspace (whose dimensionality can be chosen at will). Moreover, we show that the two-photon driving requirement can be relaxed and that full controllability is achievable with only 1-photon (linear) drives. We make use of both Trotter-Suzuki decompositions and gradient-based optimization to find control pulses for a desired gate, which reduces the computational overhead by using a small blockaded subspace. We also discuss the infidelity arising from input power limitations in realistic settings, as well as from corrections to the rotating-wave approximation. Our universal control protocol opens the possibility for quantum information processing using a wide range of lossy systems with weak nonlinearities. Source arXiv: 2312.15783v1
Classical capacity of quantum non-Gaussian attenuator and amplifier channels Authors Zacharie Van Herstraeten, Saikat Guha, Nicolas J. Cerf Published: 12.25.2023 Updated: 12.25.2023 Summary We consider a quantum bosonic channel that couples the input mode via a beam splitter or two-mode squeezer to an environmental mode that is prepared in an arbitrary state. We investigate the classical capacity of this channel, which we call a non-Gaussian attenuator or amplifier channel. If the environment state is thermal, we of course recover a Gaussian phase-covariant channel whose classical capacity is well known. Otherwise, we derive both a lower and an upper bound to the classical capacity of the channel, drawing inspiration from the classical treatment of the capacity of non-Gaussian additive-noise channels. We show that the lower bound to the capacity is always achievable and give examples where the non-Gaussianity of the channel can be exploited so that the communication rate beats the capacity of the Gaussian-equivalent channel (i.e., the channel where the environment state is replaced by a Gaussian state with the same covariance matrix). Finally, our upper bound leads us to formulate and investigate conjectures on the input state that minimizes the output entropy of non-Gaussian attenuator or amplifier channels. Solving these conjectures would be a main step towards accessing the capacity of a large class of non-Gaussian bosonic channels. Source arXiv: 2312.15623v1
Optimal noisy entanglement testing for ranging and communication Authors Pengcheng Liao, Quntao Zhuang Published: 12.22.2023 Updated: 12.22.2023 Summary Given a quantum system $S$ entangled with another system $I$, the entanglement testing problem arises, prompting the identification of the system $S$ within a set of $m ge 2$ identical systems. This scenario serves as a model for the measurement task encountered in quantum ranging and entanglement-assisted communication [Phys. Rev. Lett. 126, 240501, (2021)]. In this context, the optimal measurement approach typically involves joint measurements on all $m+1$ systems. However, we demonstrate that this is not the case when the subsystems containing system $S$ are subjected to entanglement-breaking noise. Our approach utilizes the recently developed measurement technique of correlation-to-displacement conversion. We present a structured design for the entanglement testing measurement, implementable with local operations and classical communications (LOCC) on the $m+1$ systems. Furthermore, we prove that this measurement approach achieves optimality in terms of error probability asymptotically under noisy conditions. When applied to quantum illumination, our measurement design enables optimal ranging in scenarios with low signal brightness and high levels of noise. Similarly, when applied to entanglement-assisted classical communication, the measurement design leads to a significant relative advantage in communication rates, particularly in scenarios with low signal brightness. Source arXiv: 2312.15047v1
High-fidelity, multi-qubit generalized measurements with dynamic circuits Authors Petr Ivashkov, Gideon Uchehara, Liang Jiang, Derek S. Wang, Alireza Seif Published: 12.21.2023 Updated: 12.21.2023 Summary Generalized measurements, also called positive operator-valued measures (POVMs), can offer advantages over projective measurements in various quantum information tasks. Here, we realize a generalized measurement of one and two superconducting qubits with high fidelity and in a single experimental setting. To do so, we propose a hybrid method, the “Naimark-terminated binary tree,” based on a hybridization of Naimark’s dilation and binary tree techniques that leverages emerging hardware capabilities for mid-circuit measurements and feed-forward control. Furthermore, we showcase a highly effective use of approximate compiling to enhance POVM fidelity in noisy conditions. We argue that our hybrid method scales better toward larger system sizes than its constituent methods and demonstrate its advantage by performing detector tomography of symmetric, informationally complete POVM (SIC-POVM). Detector fidelity is further improved through a composite error mitigation strategy that incorporates twirling and a newly devised conditional readout error mitigation. Looking forward, we expect improvements in approximate compilation and hardware noise for dynamic circuits to enable generalized measurements of larger multi-qubit POVMs on superconducting qubits. Source arXiv: 2312.14087v1
Quantum entanglement between optical and microwave photonic qubits Authors Srujan Meesala, David Lake, Steven Wood, Piero Chiappina, Changchun Zhong, Andrew D. Beyer, Matthew D. Shaw, Liang Jiang, Oskar Painter Published: 12.21.2023 Updated: 12.21.2023 Summary Entanglement is an extraordinary feature of quantum mechanics. Sources of entangled optical photons were essential to test the foundations of quantum physics through violations of Bell’s inequalities. More recently, entangled many-body states have been realized via strong non-linear interactions in microwave circuits with superconducting qubits. Here we demonstrate a chip-scale source of entangled optical and microwave photonic qubits. Our device platform integrates a piezo-optomechanical transducer with a superconducting resonator which is robust under optical illumination. We drive a photon-pair generation process and employ a dual-rail encoding intrinsic to our system to prepare entangled states of microwave and optical photons. We place a lower bound on the fidelity of the entangled state by measuring microwave and optical photons in two orthogonal bases. This entanglement source can directly interface telecom wavelength time-bin qubits and GHz frequency superconducting qubits, two well-established platforms for quantum communication and computation, respectively. Source arXiv: 2312.13559v1
Vacuum Beam Guide for Large-Scale Quantum Networks Authors Yuexun Huang, Francisco Salces--Carcoba, Rana X Adhikari, Amir H. Safavi-Naeini, Liang Jiang Published: 12.14.2023 Updated: 12.22.2023 Summary The vacuum beam guide (VBG) presents a completely different solution for quantum channels to overcome the limitations of existing fiber and satellite technologies for long-distance quantum communication. With an array of aligned lenses spaced kilometers apart, the VBG offers ultra-high transparency over a wide range of optical wavelengths. With realistic parameters, the VBG can outperform the best fiber by three orders of magnitude in terms of attenuation rate. Consequently, the VBG can enable long-range quantum communication over thousands of kilometers with quantum channel capacity beyond $10^{13}$ qubit/sec, orders of magnitude higher than the state-of-the-art quantum satellite communication rate. Remarkably, without relying on quantum repeaters, the VBG can provide a ground-based, low-loss, high-bandwidth quantum channel that enables novel distributed quantum information applications for computing, communication, and sensing. Source arXiv: 2312.09372v2
Quantum-centric Supercomputing for Materials Science: A Perspective on Challenges and Future Directions Authors Yuri Alexeev, Maximilian Amsler, Paul Baity, Marco Antonio Barroca, Sanzio Bassini, Torey Battelle, Daan Camps, David Casanova, Young jai Choi, Frederic T. Chong, Charles Chung, Chris Codella, Antonio D. Corcoles, James Cruise, Alberto Di Meglio, Jonathan Dubois, Ivan Duran, Thomas Eckl, Sophia Economou, Stephan Eidenbenz, Bruce Elmegreen, Clyde Fare, Ismael Faro, Cristina Sanz Fernández, Rodrigo Neumann Barros Ferreira, Keisuke Fuji, Bryce Fuller, Laura Gagliardi, Giulia Galli, Jennifer R. Glick, Isacco Gobbi, Pranav Gokhale, Salvador de la Puente Gonzalez, Johannes Greiner, Bill Gropp, Michele Grossi, Emmanuel Gull, Burns Healy, Benchen Huang, Travis S. Humble, Nobuyasu Ito, Artur F. Izmaylov, Ali Javadi-Abhari, Douglas Jennewein, Shantenu Jha, Liang Jiang, Barbara Jones, Wibe Albert de Jong, Petar Jurcevic, William Kirby, Stefan Kister, Masahiro Kitagawa, Joel Klassen, Katherine Klymko, Kwangwon Koh, Masaaki Kondo, Doga Murat Kurkcuoglu, Krzysztof Kurowski, Teodoro Laino, Ryan Landfield, Matt Leininger, Vicente Leyton-Ortega, Ang Li, Meifeng Lin, Junyu Liu, Nicolas Lorente, Andre Luckow, Simon Martiel, Francisco Martin-Fernandez, Margaret Martonosi, Claire Marvinney, Arcesio Castaneda Medina, Dirk Merten, Antonio Mezzacapo, Kristel Michielsen, Abhishek Mitra, Tushar Mittal, Kyungsun Moon, Joel Moore, Mario Motta, Young-Hye Na, Yunseong Nam, Prineha Narang, Yu-ya Ohnishi, Daniele Ottaviani, Matthew Otten, Scott Pakin, Vincent R. Pascuzzi, Ed Penault, Tomasz Piontek, Jed Pitera, Patrick Rall, Gokul Subramanian Ravi, Niall Robertson, Matteo Rossi, Piotr Rydlichowski, Hoon Ryu, Georgy Samsonidze, Mitsuhisa Sato, Nishant Saurabh, Vidushi Sharma, Kunal Sharma, Soyoung Shin, George Slessman, Mathias Steiner, Iskandar Sitdikov, In-Saeng Suh, Eric Switzer, Wei Tang, Joel Thompson, Synge Todo, Minh Tran, Dimitar Trenev, Christian Trott, Huan-Hsin Tseng, Esin Tureci, David García Valinas, Sofia Vallecorsa, Christopher Wever, Konrad Wojciechowski, Xiaodi Wu, Shinjae Yoo, Nobuyuki Yoshioka, Victor Wen-zhe Yu, Seiji Yunoki, Sergiy Zhuk, Dmitry Zubarev Published: 12.14.2023 Updated: 12.14.2023 Summary Computational models are an essential tool for the design, characterization, and discovery of novel materials. Hard computational tasks in materials science stretch the limits of existing high-performance supercomputing centers, consuming much of their simulation, analysis, and data resources. Quantum computing, on the other hand, is an emerging technology with the potential to accelerate many of the computational tasks needed for materials science. In order to do that, the quantum technology must interact with conventional high-performance computing in several ways: approximate results validation, identification of hard problems, and synergies in quantum-centric supercomputing. In this paper, we provide a perspective on how quantum-centric supercomputing can help address critical computational problems in materials science, the challenges to face in order to solve representative use cases, and new suggested directions. Source arXiv: 2312.09733v1
Alignment-Free Coupling to Arrays of Diamond Microdisk Cavities for Scalable Spin-Photon Interfaces Authors Helaman R. Flores, Samuel R. Layton, Dirk Englund, Ryan M. Camacho Published: 12.09.2023 Updated: 12.09.2023 Summary We propose a scalable design for a spin-photon interface to a color center in a diamond microdisk. The design consists of a silicon oxynitride hexagonal lattice overlaid on a diamond microdisk to enable vertical emission from the microdisk into low-numerical aperture modes, with quantum efficiencies as high as 45% for a tin vacancy (SnV) center. Our design is robust to manufacturing errors, potentially enabling large scale fabrication of quantum emitters coupled to optical collection modes. We also introduce a novel approach for optimizing the free space performance of a complex structure using a dipole model, achieving comparable results to full-wave finite difference time domain simulations with a 650,000 times reduction in computational time. Source arXiv: 2312.05638v1
Closed-Loop Electron-Beam-Induced Spectroscopy and Nanofabrication Around Individual Quantum Emitters Authors Jawaher Almutlaq, Kyle P. Kelley, Hyeongrak Choi, Linsen Li, Benjamin Lawrie, Ondrej Dyck, Dirk Englund, Stephen Jesse Published: 12.08.2023 Updated: 12.08.2023 Summary Color centers in diamond play a central role in the development of quantum photonic technologies, and their importance is only expected to grow in the near future. For many quantum applications, high collection efficiency from individual emitters is required, but the refractive index mismatch between diamond and air limits the optimal collection efficiency with conventional diamond device geometries. While different out-coupling methods with near-unity efficiency exist, many have yet to be realized due to current limitations in nanofabrication methods, especially for mechanically hard materials like diamond. Here, we leverage electron-beam-induced etching to modify Sn-implanted diamond quantum microchiplets containing integrated waveguides with width and thickness of 280 nm and 200 nm, respectively. This approach allows for simultaneous high-resolution imaging and modification of the host matrix with an open geometry and direct writing. When coupled with the cathodoluminescence signal generated from the electron-emitter interactions, we can monitor the enhancement of the quantum emitters in real-time with nanoscale spatial resolution. The operando measurement and manipulation of single photon emitters demonstrated here provides a new foundation for the control of emitter-cavity interactions in integrated quantum photonics. Source arXiv: 2312.05205v1
Clifford Manipulations of Stabilizer States: A graphical rule book for Clifford unitaries and measurements on cluster states, and application to photonic quantum computing Authors Ashlesha Patil, Saikat Guha Published: 12.04.2023 Updated: 12.04.2023 Summary Stabilizer states along with Clifford manipulations (unitary transformations and measurements) thereof — despite being efficiently simulable on a classical computer — are an important tool in quantum information processing, with applications to quantum computing, error correction and networking. Cluster states, defined on a graph, are a special class of stabilizer states that are central to measurement based quantum computing, all-photonic quantum repeaters, distributed quantum computing, and entanglement distribution in a network. All cluster states are local-Clifford equivalent to a stabilizer state. In this paper, we review the stabilizer framework, and extend it, by: incorporating general stabilizer measurements such as multi-qubit fusions, and providing an explicit procedure — using Karnaugh maps from Boolean algebra — for converting arbitrary stabilizer gates into tableau operations of the CHP formalism for efficient stabilizer manipulations. Using these tools, we develop a graphical rule-book and a MATLAB simulator with a graphical user interface for arbitrary stabilizer manipulations of cluster states, a user of which, e.g., for research in quantum networks, will not require any background in quantum information or the stabilizer framework. We extend our graphical rule-book to include dual-rail photonic-qubit cluster state manipulations with probabilistically-heralded linear-optical circuits for various rotated Bell measurements, i.e., fusions (including new `Type-I’ fusions we propose, where only one of the two fused qubits is destructively measured), by incorporating graphical rules for their success and failure modes. Finally, we show how stabilizer descriptions of multi-qubit fusions can be mapped to linear optical circuits. Source arXiv: 2312.02377v1
Majorization theoretical approach to entanglement enhancement via local filtration Authors Zacharie Van Herstraeten, Nicolas J. Cerf, Saikat Guha, Christos N. Gagatsos Published: 12.04.2023 Updated: 12.04.2023 Summary From the perspective of majorization theory, we study how to enhance the entanglement of a two-mode squeezed vacuum (TMSV) state by using local filtration operations. We present several schemes achieving entanglement enhancement with photon addition and subtraction, and then consider filtration as a general probabilistic procedure consisting in acting with local (non-unitary) operators on each mode. From this, we identify a sufficient set of two conditions on filtration operators for successfully enhancing the entanglement of a TMSV state, namely the operators must be Fock-orthogonal (i.e., preserving the orthogonality of Fock states) and Fock-amplifying (i.e., giving larger amplitudes to larger Fock states). Our results notably prove that ideal photon addition, subtraction, and any concatenation thereof always enhance the entanglement of a TMSV state in the sense of majorization theory. We further investigate the case of realistic photon addition (subtraction) and are able to upper bound the distance between a realistic photon-added (-subtracted) TMSV state and a nearby state that is provably more entangled than the TMSV, thus extending entanglement enhancement to practical schemes via the use of a notion of approximate majorization. Finally, we consider the state resulting from $k$-photon addition (on each of the two modes) on a TMSV state. We prove analytically that the state corresponding to $k=1$ majorizes any state corresponding to $2leq k leq 8$ and we conjecture the validity of the statement for all $kgeq 9$. Source arXiv: 2312.02066v1
Co-Designed Superconducting Architecture for Lattice Surgery of Surface Codes with Quantum Interface Routing Card Authors Charles Guinn, Samuel Stein, Esin Tureci, Guus Avis, Chenxu Liu, Stefan Krastanov, Andrew A. Houck, Ang Li Published: 12.02.2023 Updated: 12.02.2023 Summary Facilitating the ability to achieve logical qubit error rates below physical qubit error rates, error correction is anticipated to play an important role in scaling quantum computers. While many algorithms require millions of physical qubits to be executed with error correction, current superconducting qubit systems contain only hundreds of physical qubits. One of the most promising codes on the superconducting qubit platform is the surface code, requiring a realistically attainable error threshold and the ability to perform universal fault-tolerant quantum computing with local operations via lattice surgery and magic state injection. Surface code architectures easily generalize to single-chip planar layouts, however space and control hardware constraints point to limits on the number of qubits that can fit on one chip. Additionally, the planar routing on single-chip architectures leads to serialization of commuting gates and strain on classical decoding caused by large ancilla patches. A distributed multi-chip architecture utilizing the surface code can potentially solve these problems if one can optimize inter-chip gates, manage collisions in networking between chips, and minimize routing hardware costs. We propose QuIRC, a superconducting Quantum Interface Routing Card for Lattice Surgery between surface code modules inside of a single dilution refrigerator. QuIRC improves scaling by allowing connection of many modules, increases ancilla connectivity of surface code lattices, and offers improved transpilation of Pauli-based surface code circuits. QuIRC employs in-situ Entangled Pair (EP) generation protocols for communication. We explore potential topological layouts of QuIRC based on superconducting hardware fabrication constraints, and demonstrate reductions in ancilla patch size by up to 77.8%, and in layer transpilation size by 51.9% when compared to the single-chip case. Source arXiv: 2312.01246v1
Nanoscale confinement and control of excitonic complexes in a monolayer WSe2 Authors Hyowon Moon, Lukas Mennel, Chitraleema Chakraborty, Cheng Peng, Jawaher Almutlaq, Takashi Taniguchi, Kenji Watanabe, Dirk Englund Published: 11.30.2023 Updated: 11.30.2023 Summary Nanoscale control and observation of photophysical processes in semiconductors is critical for basic understanding and applications from optoelectronics to quantum information processing. In particular, there are open questions and opportunities in controlling excitonic complexes in two-dimensional materials such as excitons, trions or biexcitons. However, neither conventional diffraction-limited optical spectroscopy nor lithography-limited electric control provides a proper tool to investigate these quasiparticles at the nanometer-scale at cryogenic temperature. Here, we introduce a cryogenic capacitive confocal optical microscope (C3OM) as a tool to study quasiparticle dynamics at the nanometer scale. Using a conductive atomic force microscope (AFM) tip as a gate electrode, we can modulate the electronic doping at the nanometer scale in WSe2 at 4K. This tool allows us to modulate with nanometer-scale confinement the exciton and trion peaks, as well a distinct photoluminescence line associated with a larger excitonic complex that exhibits distinctive nonlinear optical response. Our results demonstrate nanoscale confinement and spectroscopy of exciton complexes at arbitrary positions, which should prove an important tool for quantitative understanding of complex optoelectronic properties in semiconductors as well as for applications ranging from quantum spin liquids to superresolution measurements to control of quantum emitters. Source arXiv: 2311.18660v1
Low-Complexity Linear Programming Based Decoding of Quantum LDPC codes Authors Sana Javed, Francisco Garcia-Herrero, Bane Vasic, Mark F. Flanagan Published: 11.30.2023 Updated: 01.19.2024 Summary This paper proposes two approaches for reducing the impact of the error floor phenomenon when decoding quantum low-density parity-check codes with belief propagation based algorithms. First, a low-complexity syndrome-based linear programming (SB-LP) decoding algorithm is proposed, and second, the proposed SB-LP is applied as a post-processing step after syndrome-based min-sum (SB-MS) decoding. For the latter case, a new early stopping criterion is introduced to decide when to activate the SB-LP algorithm, avoiding executing a predefined maximum number of iterations for the SB-MS decoder. Simulation results show, for a sample hypergraph code, that the proposed decoder can lower the error floor by two to three orders of magnitude compared to SB-MS for the same total number of decoding iterations. Source arXiv: 2311.18488v2
Dynamical phase transition in quantum neural networks with large depth Authors Bingzhi Zhang, Junyu Liu, Xiao-Chuan Wu, Liang Jiang, Quntao Zhuang Published: 11.29.2023 Updated: 11.29.2023 Summary Understanding the training dynamics of quantum neural networks is a fundamental task in quantum information science with wide impact in physics, chemistry and machine learning. In this work, we show that the late-time training dynamics of quantum neural networks can be described by the generalized Lotka-Volterra equations, which lead to a dynamical phase transition. When the targeted value of cost function crosses the minimum achievable value from above to below, the dynamics evolve from a frozen-kernel phase to a frozen-error phase, showing a duality between the quantum neural tangent kernel and the total error. In both phases, the convergence towards the fixed point is exponential, while at the critical point becomes polynomial. Via mapping the Hessian of the training dynamics to a Hamiltonian in the imaginary time, we reveal the nature of the phase transition to be second-order with the exponent $nu=1$, where scale invariance and closing gap are observed at critical point. We also provide a non-perturbative analytical theory to explain the phase transition via a restricted Haar ensemble at late time, when the output state approaches the steady state. The theory findings are verified experimentally on IBM quantum devices. Source arXiv: 2311.18144v1
On-Chip Backward Stimulated Brillouin Scattering in Lithium Niobate Waveguides Authors Caique C. Rodrigues, Nick J. Schilder, Roberto O. Zurita, Letícia S. Magalhães, Amirhassan Shams-Ansari, Thiago P. M. Alegre, Marko Lončar, Gustavo S. Wiederhecker Published: 11.29.2023 Updated: 11.29.2023 Summary We report on the first experimental demonstration of backward stimulated Brillouin scattering (SBS) in Lithium Niobate on Insulator (LNOI) waveguides. Performing polarization-dependent pump-probe experiments, we successfully quantified both intramodal and intermodal scattering among fundamental modes, showcasing substantial gains up to $G_{B}=$10m$^{-1}$W$^{-1}$. Such large gains on simple waveguides open a pathway for unlocking novel opto-electro-mechanical phenomena within the LNOI platform. Source arXiv: 2311.18135v1
Heisenberg-Limited Quantum Lidar for Joint Range and Velocity Estimation Authors Maximilian Reichert, Quntao Zhuang, Mikel Sanz Published: 11.24.2023 Updated: 11.24.2023 Summary We propose a quantum lidar protocol to jointly estimate the range and velocity of a target by illuminating it with a single beam of pulsed displaced squeezed light. In the lossless scenario, we show that the mean-squared errors of both range and velocity estimations are inversely proportional to the squared number of signal photons, simultaneously attaining the Heisenberg limit. This is achieved by engineering the multi-photon squeezed state of the temporal modes and adopting standard homodyne detection. To assess the robustness of the quantum protocol, we incorporate photon losses and detuning of the homodyne receiver. Our findings reveal a quantum advantage over the best-known classical strategy across a wide range of round-trip transmissivities. Particularly, the quantum advantage is substantial for sufficiently small losses, even when compared to the optimal — potentially unattainable — classical performance limit. The quantum advantage also extends to the practical case where quantum engineering is done on top of the strong classical coherent state with watts of power. This, together with the robustness against losses and the feasibility of the measurement with state-of-the-art technology, make the protocol highly promising for near-term implementation. Source arXiv: 2311.14546v1
Deep Learning Architecture for Network-Efficiency at the Edge Authors Akrit Mudvari, Antero Vainio, Iason Ofeidis, Sasu Tarkoma, Leandros Tassiulas Published: 11.09.2023 Updated: 01.15.2024 Summary The growing number of AI-driven applications in the mobile devices has led to solutions that integrate deep learning models with the available edge-cloud resources; due to multiple benefits such as reduction in on-device energy consumption, improved latency, improved network usage, and certain privacy improvements, split learning, where deep learning models are split away from the mobile device and computed in a distributed manner, has become an extensively explored topic. Combined with compression-aware methods where learning adapts to compression of communicated data, the benefits of this approach have further improved and could serve as an alternative to established approaches like federated learning methods. In this work, we develop an adaptive compression-aware split learning method (‘deprune’) to improve and train deep learning models so that they are much more network-efficient (use less network resources and are faster), which would make them ideal to deploy in weaker devices with the help of edge-cloud resources. This method is also extended (‘prune’) to very quickly train deep learning models, through a transfer learning approach, that trades off little accuracy for much more network-efficient inference abilities. We show that the ‘deprune’ method can reduce network usage by 4x when compared with a split-learning approach (that does not use our method) without loss of accuracy, while also improving accuracy over compression-aware split-learning by 4 percent. Lastly, we show that the ‘prune’ method can reduce the training time for certain models by up to 6x without affecting the accuracy when compared against a compression-aware split-learning approach. Source arXiv: 2311.05739v3
Adaptive Compression-Aware Split Learning and Inference for Enhanced Network Efficiency Authors Akrit Mudvari, Antero Vainio, Iason Ofeidis, Sasu Tarkoma, Leandros Tassiulas Published: 11.09.2023 Updated: 02.01.2024 Summary The growing number of AI-driven applications in mobile devices has led to solutions that integrate deep learning models with the available edge-cloud resources. Due to multiple benefits such as reduction in on-device energy consumption, improved latency, improved network usage, and certain privacy improvements, split learning, where deep learning models are split away from the mobile device and computed in a distributed manner, has become an extensively explored topic. Incorporating compression-aware methods (where learning adapts to compression level of the communicated data) has made split learning even more advantageous. This method could even offer a viable alternative to traditional methods, such as federated learning techniques. In this work, we develop an adaptive compression-aware split learning method (‘deprune’) to improve and train deep learning models so that they are much more network-efficient, which would make them ideal to deploy in weaker devices with the help of edge-cloud resources. This method is also extended (‘prune’) to very quickly train deep learning models through a transfer learning approach, which trades off little accuracy for much more network-efficient inference abilities. We show that the ‘deprune’ method can reduce network usage by 4x when compared with a split-learning approach (that does not use our method) without loss of accuracy, while also improving accuracy over compression-aware split-learning by 4 percent. Lastly, we show that the ‘prune’ method can reduce the training time for certain models by up to 6x without affecting the accuracy when compared against a compression-aware split-learning approach. Source arXiv: 2311.05739v4
Mobility as a Resource (MaaR) for resilient human-centric automation: a vision paper Authors S. Travis Waller, Amalia Polydoropoulou, Leandros Tassiulas, Athanasios Ziliaskopoulos, Sisi Jian, Susann Wagenknecht, Georg Hirte, Satish Ukkusuri, Gitakrishnan Ramadurai, Tomasz Bednarz Published: 11.05.2023 Updated: 03.03.2024 Summary With technological advances, mobility has been moving from a product (i.e., traditional modes and vehicles), to a service (i.e., Mobility as a Service, MaaS). However, as observed in other fields (e.g. cloud computing resource management) we argue that mobility will evolve from a service to a resource (i.e., Mobility as a Resource, MaaR). Further, due to increasing scarcity of shared mobility spaces across traditional and emerging modes, the transition must be viewed within the critical need for ethical and equitable solutions for the traveling public (i.e., research is needed to avoid hyper-market driven outcomes for society). The evolution of mobility into a resource requires novel conceptual frameworks, technologies, processes and perspectives of analysis. A key component of the future MaaR system is the technological capacity to observe, allocate and manage (in real-time) the smallest envisionable units of mobility (i.e., atomic units of mobility capacity) while providing prioritized attention to human movement and ethical metrics related to access, consumption and impact. To facilitate research into the envisioned future system, this paper proposes initial frameworks which synthesize and advance methodologies relating to highly dynamic capacity reservation systems. Future research requires synthesis across transport network management, demand behavior, mixed-mode usage, and equitable mobility. Source arXiv: 2311.02786v2
Performance limits due to thermal transport in graphene single-photon bolometers Authors Caleb Fried, B. Jordan Russell, Ethan G. Arnault, Bevin Huang, Gil-Ho Lee, Dirk Englund, Erik A. Henriksen, Kin Chung Fong Published: 11.01.2023 Updated: 12.18.2023 Summary In high-sensitivity bolometers and calorimeters, the photon absorption often occurs at a finite distance from the temperature sensor to accommodate antennas or avoid the degradation of superconducting circuitry exposed to radiation. As a result, thermal propagation from the input to the temperature readout can critically affect detector performance. In this report we model the performance of a graphene bolometer, accounting for electronic thermal diffusion and dissipation via electron-phonon coupling at low temperatures in three regimes: clean, supercollision, and resonant scattering. Our results affirm the feasibility of a superconducting readout without Cooper-pair breaking by mid- and near-infrared photons, and provide a recipe for designing graphene absorbers for calorimetric single-photon detectors. We investigate the tradeoff between the input-readout distance and detector efficiency, and predict an intrinsic timing jitter of ~2.7 ps. Based on our result, we propose a spatial-mode-resolving photon detector to increase communication bandwidth. Source arXiv: 2311.00228v2
Performance limits due to thermal transport in graphene single-photon bolometers Authors Caleb Fried, B. Jordan Russell, Ethan G. Arnault, Bevin Huang, Gil-Ho Lee, Dirk Englund, Erik A. Henriksen, Kin Chung Fong Published: 11.01.2023 Updated: 01.15.2024 Summary In high-sensitivity bolometers and calorimeters, the photon absorption often occurs at a finite distance from the temperature sensor to accommodate antennas or avoid the degradation of superconducting circuitry exposed to radiation. As a result, thermal propagation from the input to the temperature readout can critically affect detector performance. In this report we model the performance of a graphene bolometer, accounting for electronic thermal diffusion and dissipation via electron-phonon coupling at low temperatures in three regimes: clean, supercollision, and resonant scattering. Our results affirm the feasibility of a superconducting readout without Cooper-pair breaking by mid- and near-infrared photons, and provide a recipe for designing graphene absorbers for calorimetric single-photon detectors. We investigate the tradeoff between the input-readout distance and detector efficiency, and predict an intrinsic timing jitter of ~2.7 ps. Based on our result, we propose a spatial-mode-resolving photon detector to increase communication bandwidth. Source arXiv: 2311.00228v3
Fault-Tolerant Operation of Bosonic Qubits with Discrete-Variable Ancillae Authors Qian Xu, Pei Zeng, Daohong Xu, Liang Jiang Published: 10.31.2023 Updated: 10.31.2023 Summary Fault-tolerant quantum computation with bosonic qubits often necessitates the use of noisy discrete-variable ancillae. In this work, we establish a comprehensive and practical fault-tolerance framework for such a hybrid system and synthesize it with fault-tolerant protocols by combining bosonic quantum error correction (QEC) and advanced quantum control techniques. We introduce essential building blocks of error-corrected gadgets by leveraging ancilla-assisted bosonic operations using a generalized variant of path-independent quantum control (GPI). Using these building blocks, we construct a universal set of error-corrected gadgets that tolerate a single photon loss and an arbitrary ancilla fault for four-legged cat qubits. Notably, our construction only requires dispersive coupling between bosonic modes and ancillae, as well as beam-splitter coupling between bosonic modes, both of which have been experimentally demonstrated with strong strengths and high accuracy. Moreover, each error-corrected bosonic qubit is only comprised of a single bosonic mode and a three-level ancilla, featuring the hardware efficiency of bosonic QEC in the full fault-tolerant setting. We numerically demonstrate the feasibility of our schemes using current experimental parameters in the circuit-QED platform. Finally, we present a hardware-efficient architecture for fault-tolerant quantum computing by concatenating the four-legged cat qubits with an outer qubit code utilizing only beam-splitter couplings. Our estimates suggest that the overall noise threshold can be reached using existing hardware. These developed fault-tolerant schemes extend beyond their applicability to four-legged cat qubits and can be adapted for other rotation-symmetrical codes, offering a promising avenue toward scalable and robust quantum computation with bosonic qubits. Source arXiv: 2310.20578v1
Age Optimum Sampling in Non-Stationary Environment Authors Jinheng Zhang, Haoyue Tang, Jintao Wang, Sastry Kompella, Leandros Tassiulas Published: 10.31.2023 Updated: 10.31.2023 Summary In this work, we consider a status update system with a sensor and a receiver. The status update information is sampled by the sensor and then forwarded to the receiver through a channel with non-stationary delay distribution. The data freshness at the receiver is quantified by the Age-of-Information (AoI). The goal is to design an online sampling strategy that can minimize the average AoI when the non-stationary delay distribution is unknown. Assuming that channel delay distribution may change over time, to minimize the average AoI, we propose a joint stochastic approximation and non-parametric change point detection algorithm that can: (1) learn the optimum update threshold when the delay distribution remains static; (2) detect the change in transmission delay distribution quickly and then restart the learning process. Simulation results show that the proposed algorithm can quickly detect the delay changes, and the average AoI obtained by the proposed policy converges to the minimum AoI. Source arXiv: 2310.20275v1
Electrical Tuning of Neutral and Charged Excitons with 1-nm Gate Authors Jawaher Almutlaq, Jiangtao Wang, Linsen Li, Chao Li, Tong Dang, Vladimir Bulović, Jing Kong, Dirk Englund Published: 10.30.2023 Updated: 10.30.2023 Summary Electrical control of individual spins and photons in solids is key for quantum technologies, but scaling down to small, static systems remains challenging. Here, we demonstrate nanoscale electrical tuning of neutral and charged excitons in monolayer WSe2 using 1-nm carbon nanotube gates. Electrostatic simulations reveal a confinement radius below 15 nm, reaching the exciton Bohr radius limit for few-layer dielectric spacing. In situ photoluminescence spectroscopy shows gate-controlled conversion between neutral excitons, negatively charged trions, and biexcitons at 4 K. Important for quantum information processing applications, our measurements indicate gating of a local 2D electron gas in the WSe2 layer, coupled to photons via trion transitions with binding energies exceeding 20 meV. The ability to deterministically tune and address quantum emitters using nanoscale gates provides a pathway towards large-scale quantum optoelectronic circuits and spin-photon interfaces for quantum networking. Source arXiv: 2310.19895v1
Tutorial: Remote entanglement protocols for stationary qubits with photonic interfaces Authors Hans K. C. Beukers, Matteo Pasini, Hyeongrak Choi, Dirk Englund, Ronald Hanson, Johannes Borregaard Published: 10.30.2023 Updated: 10.30.2023 Summary Generating entanglement between distant quantum systems is at the core of quantum networking. In recent years, numerous theoretical protocols for remote entanglement generation have been proposed, of which many have been experimentally realized. Here, we provide a modular theoretical framework to elucidate the general mechanisms of photon-mediated entanglement generation between single spins in atomic or solid-state systems. Our framework categorizes existing protocols at various levels of abstraction and allows for combining the elements of different schemes in new ways. These abstraction layers make it possible to readily compare protocols for different quantum hardware. To enable the practical evaluation of protocols tailored to specific experimental parameters, we have devised numerical simulations based on the framework with our codes available online. Source arXiv: 2310.19878v1
High Q-factor diamond optomechanical resonators with silicon vacancy centers at millikelvin temperatures Authors Graham D. Joe, Cleaven Chia, Benjamin Pingault, Michael Haas, Michelle Chalupnik, Eliza Cornell, Kazuhiro Kuruma, Bartholomeus Machielse, Neil Sinclair, Srujan Meesala, Marko Lončar Published: 10.28.2023 Updated: 10.28.2023 Summary Phonons are envisioned as coherent intermediaries between different types of quantum systems. Engineered nanoscale devices such as optomechanical crystals (OMCs) provide a platform to utilize phonons as quantum information carriers. Here we demonstrate OMCs in diamond designed for strong interactions between phonons and a silicon vacancy (SiV) spin. Using optical measurements at millikelvin temperatures, we measure a linewidth of 13 kHz (Q-factor of ~440,000) for 6 GHz acoustic modes, a record for diamond in the GHz frequency range and within an order of magnitude of state-of-the-art linewidths for OMCs in silicon. We investigate SiV optical and spin properties in these devices and outline a path towards a coherent spin-phonon interface. Source arXiv: 2310.18838v1
Coherent control of a superconducting qubit using light Authors Hana K. Warner, Jeffrey Holzgrafe, Beatriz Yankelevich, David Barton, Stefano Poletto, C. J. Xin, Neil Sinclair, Di Zhu, Eyob Sete, Brandon Langley, Emma Batson, Marco Colangelo, Amirhassan Shams-Ansari, Graham Joe, Karl K. Berggren, Liang Jiang, Matthew Reagor, Marko Loncar Published: 10.24.2023 Updated: 10.24.2023 Summary Quantum science and technology promise the realization of a powerful computational resource that relies on a network of quantum processors connected with low loss and low noise communication channels capable of distributing entangled states [1,2]. While superconducting microwave qubits (3-8 GHz) operating in cryogenic environments have emerged as promising candidates for quantum processor nodes due to their strong Josephson nonlinearity and low loss [3], the information between spatially separated processor nodes will likely be carried at room temperature via telecommunication photons (200 THz) propagating in low loss optical fibers. Transduction of quantum information [4-10] between these disparate frequencies is therefore critical to leverage the advantages of each platform by interfacing quantum resources. Here, we demonstrate coherent optical control of a superconducting qubit. We achieve this by developing a microwave-optical quantum transducer that operates with up to 1.18% conversion efficiency (1.16% cooperativity) and demonstrate optically-driven Rabi oscillations (2.27 MHz) in a superconducting qubit without impacting qubit coherence times (800 ns). Finally, we discuss outlooks towards using the transducer to network quantum processor nodes. Source arXiv: 2310.16155v1
Coherent control of a superconducting qubit using light Authors Hana K. Warner, Jeffrey Holzgrafe, Beatriz Yankelevich, David Barton, Stefano Poletto, C. J. Xin, Neil Sinclair, Di Zhu, Eyob Sete, Brandon Langley, Emma Batson, Marco Colangelo, Amirhassan Shams-Ansari, Graham Joe, Karl K. Berggren, Liang Jiang, Matthew Reagor, Marko Loncar Published: 10.24.2023 Updated: 10.30.2023 Summary Quantum science and technology promise the realization of a powerful computational resource that relies on a network of quantum processors connected with low loss and low noise communication channels capable of distributing entangled states [1,2]. While superconducting microwave qubits (3-8 GHz) operating in cryogenic environments have emerged as promising candidates for quantum processor nodes due to their strong Josephson nonlinearity and low loss [3], the information between spatially separated processor nodes will likely be carried at room temperature via telecommunication photons (200 THz) propagating in low loss optical fibers. Transduction of quantum information [4-10] between these disparate frequencies is therefore critical to leverage the advantages of each platform by interfacing quantum resources. Here, we demonstrate coherent optical control of a superconducting qubit. We achieve this by developing a microwave-optical quantum transducer that operates with up to 1.18% conversion efficiency (1.16% cooperativity) and demonstrate optically-driven Rabi oscillations (2.27 MHz) in a superconducting qubit without impacting qubit coherence times (800 ns). Finally, we discuss outlooks towards using the transducer to network quantum processor nodes. Source arXiv: 2310.16155v2
Foundations of Quantum Federated Learning Over Classical and Quantum Networks Authors Mahdi Chehimi, Samuel Yen-Chi Chen, Walid Saad, Don Towsley, Mérouane Debbah Published: 10.23.2023 Updated: 10.23.2023 Summary Quantum federated learning (QFL) is a novel framework that integrates the advantages of classical federated learning (FL) with the computational power of quantum technologies. This includes quantum computing and quantum machine learning (QML), enabling QFL to handle high-dimensional complex data. QFL can be deployed over both classical and quantum communication networks in order to benefit from information-theoretic security levels surpassing traditional FL frameworks. In this paper, we provide the first comprehensive investigation of the challenges and opportunities of QFL. We particularly examine the key components of QFL and identify the unique challenges that arise when deploying it over both classical and quantum networks. We then develop novel solutions and articulate promising research directions that can help address the identified challenges. We also provide actionable recommendations to advance the practical realization of QFL. Source arXiv: 2310.14516v1
High-speed photonic crystal modulator with non-volatile memory via structurally-engineered strain concentration in a piezo-MEMS platform Authors Y. Henry Wen, David Heim, Matthew Zimmermann, Roman A. Shugayev, Mark Dong, Andrew J. Leenheer, Gerald Gilbert, Matt Eichenfield, Mikkel Heuck, Dirk R. Englund Published: 10.11.2023 Updated: 10.11.2023 Summary Numerous applications in quantum and classical optics require scalable, high-speed modulators that cover visible-NIR wavelengths with low footprint, drive voltage (V) and power dissipation. A critical figure of merit for electro-optic (EO) modulators is the transmission change per voltage, dT/dV. Conventional approaches in wave-guided modulators seek to maximize dT/dV by the selection of a high EO coefficient or a longer light-material interaction, but are ultimately limited by nonlinear material properties and material losses, respectively. Optical and RF resonances can improve dT/dV, but introduce added challenges in terms of speed and spectral tuning, especially for high-Q photonic cavity resonances. Here, we introduce a cavity-based EO modulator to solve both trade-offs in a piezo-strained photonic crystal cavity. Our approach concentrates the displacement of a piezo-electric actuator of length L and a given piezoelectric coefficient into the PhCC, resulting in dT/dV proportional to L under fixed material loss. Secondly, we employ a material deformation that is programmable under a “read-write” protocol with a continuous, repeatable tuning range of 5 GHz and a maximum non-volatile excursion of 8 GHz. In telecom-band demonstrations, we measure a fundamental mode linewidth = 5.4 GHz, with voltage response 177 MHz/V corresponding to 40 GHz for voltage spanning -120 to 120 V, 3dB-modulation bandwidth of 3.2 MHz broadband DC-AC, and 142 MHz for resonant operation near 2.8 GHz operation, optical extinction down to min(log(T)) = -25 dB via Michelson-type interference, and an energy consumption down to 0.17 nW/GHz. The strain-enhancement methods presented here are applicable to study and control other strain-sensitive systems. Source arXiv: 2310.07798v1
Engineering Phonon-Qubit Interactions using Phononic Crystals Authors Kazuhiro Kuruma, Benjamin Pingault, Cleaven Chia, Michael Haas, Graham D Joe, Daniel Rimoli Assumpcao, Sophie Weiyi Ding, Chang Jin, C. J. Xin, Matthew Yeh, Neil Sinclair, Marko Lončar Published: 10.10.2023 Updated: 10.10.2023 Summary The ability to control phonons in solids is key for diverse quantum applications, ranging from quantum information processing to sensing. Often, phonons are sources of noise and decoherence, since they can interact with a variety of solid-state quantum systems. To mitigate this, quantum systems typically operate at milli-Kelvin temperatures to reduce the number of thermal phonons. Here we demonstrate an alternative approach that relies on engineering phononic density of states, drawing inspiration from photonic bandgap structures that have been used to control the spontaneous emission of quantum emitters. We design and fabricate diamond phononic crystals with a complete phononic bandgap spanning 50 – 70 gigahertz, tailored to suppress interactions of a single silicon-vacancy color center with resonant phonons of the thermal bath. At 4 Kelvin, we demonstrate a reduction of the phonon-induced orbital relaxation rate of the color center by a factor of 18 compared to bulk. Furthermore, we show that the phononic bandgap can efficiently suppress phonon-color center interactions up to 20 Kelvin. In addition to enabling operation of quantum memories at higher temperatures, the ability to engineer qubit-phonon interactions may enable new functionalities for quantum science and technology, where phonons are used as carriers of quantum information. Source arXiv: 2310.06236v1
Superadditive Communications with the Green Machine: A Practical Demonstration of Nonlocality without Entanglement Authors Chaohan Cui, Jack Postlewaite, Babak N. Saif, Linran Fan, Saikat Guha Published: 10.09.2023 Updated: 11.08.2023 Summary Achieving the ultimate Holevo limit of optical communications capacity requires a joint-detection receiver: a device that makes a collective quantum measurement over multiple modulated symbols. Such superadditivity — a higher communication rate than that achievable by any physically realizable symbol-by-symbol optical detection — is a special case of the celebrated nonlocality without entanglement and has yet to be demonstrated in practice. In this article, we propose a practical design of the Green Machine — a joint-detection receiver that can attain superadditive capacity with a binary-phase-shift-keying (BPSK) modulated Hadamard code. We build this receiver and show that its capacity surpasses that of all practical symbol-by-symbol receivers in the low-received-photon-flux regime after backing out losses within our receiver. Our Green Machine receiver not only reduces the transmitter peak power requirement compared with the pulse-position modulation (the conventional modulation format used for deep space laser communications), but we show that its self-referenced phase also makes it more immune to phase noise, e.g., atmospheric turbulence or platform vibrations, by orders of magnitude compared with other BPSK-compatible receivers. Source arXiv: 2310.05889v2
Generative quantum machine learning via denoising diffusion probabilistic models Authors Bingzhi Zhang, Peng Xu, Xiaohui Chen, Quntao Zhuang Published: 10.09.2023 Updated: 10.09.2023 Summary Deep generative models are key-enabling technology to computer vision, text generation and large language models. Denoising diffusion probabilistic models (DDPMs) have recently gained much attention due to their ability to generate diverse and high-quality samples in many computer vision tasks, as well as to incorporate flexible model architectures and relatively simple training scheme. Quantum generative models, empowered by entanglement and superposition, have brought new insight to learning classical and quantum data. Inspired by the classical counterpart, we propose the quantum denoising diffusion probabilistic models (QuDDPM) to enable efficiently trainable generative learning of quantum data. QuDDPM adopts sufficient layers of circuits to guarantee expressivity, while introduces multiple intermediate training tasks as interpolation between the target distribution and noise to avoid barren plateau and guarantee efficient training. We demonstrate QuDDPM’s capability in learning correlated quantum noise model and learning topological structure of nontrivial distribution of quantum data. Source arXiv: 2310.05866v1
Generative quantum machine learning via denoising diffusion probabilistic models Authors Bingzhi Zhang, Peng Xu, Xiaohui Chen, Quntao Zhuang Published: 10.09.2023 Updated: 02.01.2024 Summary Deep generative models are key-enabling technology to computer vision, text generation and large language models. Denoising diffusion probabilistic models (DDPMs) have recently gained much attention due to their ability to generate diverse and high-quality samples in many computer vision tasks, as well as to incorporate flexible model architectures and relatively simple training scheme. Quantum generative models, empowered by entanglement and superposition, have brought new insight to learning classical and quantum data. Inspired by the classical counterpart, we propose the emph{quantum denoising diffusion probabilistic model} (QuDDPM) to enable efficiently trainable generative learning of quantum data. QuDDPM adopts sufficient layers of circuits to guarantee expressivity, while introduces multiple intermediate training tasks as interpolation between the target distribution and noise to avoid barren plateau and guarantee efficient training. We provide bounds on the learning error and demonstrate QuDDPM’s capability in learning correlated quantum noise model, quantum many-body phases and topological structure of quantum data. The results provide a paradigm for versatile and efficient quantum generative learning. Source arXiv: 2310.05866v3
Generative quantum machine learning via denoising diffusion probabilistic models Authors Bingzhi Zhang, Peng Xu, Xiaohui Chen, Quntao Zhuang Published: 10.09.2023 Updated: 02.16.2024 Summary Deep generative models are key-enabling technology to computer vision, text generation, and large language models. Denoising diffusion probabilistic models (DDPMs) have recently gained much attention due to their ability to generate diverse and high-quality samples in many computer vision tasks, as well as to incorporate flexible model architectures and a relatively simple training scheme. Quantum generative models, empowered by entanglement and superposition, have brought new insight to learning classical and quantum data. Inspired by the classical counterpart, we propose the quantum denoising diffusion probabilistic model (QuDDPM) to enable efficiently trainable generative learning of quantum data. QuDDPM adopts sufficient layers of circuits to guarantee expressivity, while it introduces multiple intermediate training tasks as interpolation between the target distribution and noise to avoid barren plateau and guarantee efficient training. We provide bounds on the learning error and demonstrate QuDDPM’s capability in learning correlated quantum noise model, quantum many-body phases, and topological structure of quantum data. The results provide a paradigm for versatile and efficient quantum generative learning. Source arXiv: 2310.05866v4
Optimization methods for the capacitated refueling station location problem with routing Authors Nicholas Nordlund, Leandros Tassiulas, Jan-Hendrik Lange Published: 10.09.2023 Updated: 10.09.2023 Summary The energy transition in transportation benefits from demand-based models to determine the optimal placement of refueling stations for alternative fuel vehicles such as battery electric trucks. A formulation known as the refueling station location problem with routing (RSLP-R) is concerned with minimizing the number of stations necessary to cover a set of origin-destination trips such that the transit time does not exceed a given threshold. In this paper we extend the RSLP-R by station capacities to limit the number of vehicles that can be refueled at individual stations. The solution to the capacitated RSLP-R (CRSLP-R) avoids congestion of refueling stations by satisfying capacity constraints. We devise two optimization methods to deal with the increased difficulty to solve the CRSLP-R. The first method extends a prior branch-and-cut approach and the second method is a branch-cut-and-price algorithm based on variables associated with feasible routes. We evaluate both our methods on instances from the literature as well as a newly constructed network and find that the relative performance of the algorithms depends on the strictness of the capacity constraints. Furthermore, we show some runtime improvements over prior work on uncapacitated instances. Source arXiv: 2310.05569v1
Metal-Optic Nanophotonic Modulators in Standard CMOS Technology Authors Mohamed ElKabbash, Sivan Trajtenberg-Mills, Isaac Harris, Saumil Bandyopadhyay, Mohamed I Ibrahim, Archer Wang, Xibi Chen, Cole Brabec, Hasan Z. Yildiz, Ruonan Han, Dirk Englund Published: 10.06.2023 Updated: 10.06.2023 Summary Integrating nanophotonics with electronics promises revolutionary applications ranging from light detection and ranging (LiDAR) to holographic displays. Although semiconductor manufacturing of nanophotonics in Silicon Photonic foundries is maturing, realizing active nanophotonics in the ubiquitous bulk CMOS processes remains challenging. We introduce a fabless approach to embed active nanophotonics in bulk CMOS by co-designing the back-end-of-line metal layers for optical functionality. Without changing any of the design rules imposed by a 65 nm CMOS process, we realize plasmonic liquid crystal modulators that exhibit switching speeds 100 times faster than commercial technologies. Our approach, which embeds ‘zero-change’ nanophotonics into the most ubiquitous platform for integrated electronics, democratizes fabrication of metal-optic nanophotonics, opens the path to mass production of active nanophotonic components, and overcomes major packaging challenges that have previously hindered the realization of complex metal-optic optoelectronic systems. Source arXiv: 2310.04409v1
Towards Distributed Quantum Computing by Qubit and Gate Graph Partitioning Techniques Authors Marc Grau Davis, Joaquin Chung, Dirk Englund, Rajkumar Kettimuthu Published: 10.05.2023 Updated: 10.05.2023 Summary Distributed quantum computing is motivated by the difficulty in building large-scale, individual quantum computers. To solve that problem, a large quantum circuit is partitioned and distributed to small quantum computers for execution. Partitions running on different quantum computers share quantum information using entangled Bell pairs. However, entanglement generation and purification introduces both a runtime and memory overhead on distributed quantum computing. In this paper we study that trade-off by proposing two techniques for partitioning large quantum circuits and for distribution to small quantum computers. Our techniques map a quantum circuit to a graph representation. We study two approaches: one that considers only gate teleportation, and another that considers both gate and state teleportation to achieve the distributed execution. Then we apply the METIS graph partitioning algorithm to obtain the partitions and the number of entanglement requests between them. We use the SeQUeNCe quantum communication simulator to measure the time required for generating all the entanglements required to execute the distributed circuit. We find that the best partitioning technique will depend on the specific circuit of interest. Source arXiv: 2310.03942v1
Coherence of Group-IV Color Centers Authors Isaac B. W. Harris, Dirk Englund Published: 10.04.2023 Updated: 10.04.2023 Summary Group-IV color centers in diamond (SiV, GeV, SnV) have emerged as leading solid-state spin-photon interfaces for quantum information processing applications. However, these qubits require cryogenic temperatures to achieve high fidelity operation due to interactions with the thermal phonon bath. In this work, we: (i) derive a detailed model of the decoherence from first-order acoustic phonon processes acting on the spin-orbit fine structure of these color centers; (ii) demonstrate agreement of the model’s predicted coherence times with previous measurements; (iii) identify regimes to suppress phonon-mediated decoherence by changing magnetic-field and strain bias to allow higher temperature operation. This methodology enables prediction of decoherence processes in other color centers and solid-state qubit systems coupled to a thermal bath via a parasitic two-level system. By experiment-anchored decoherence models, we facilitate optimizing qubit coherence for specific applications and devices. Source arXiv: 2310.02884v1
Entanglement of Nanophotonic Quantum Memory Nodes in a Telecommunication Network Authors Can M. Knaut, Aziza Suleymanzade, Yan-Cheng Wei, Daniel R. Assumpcao, Pieter-Jan Stas, Yan Qi Huan, Bartholomeus Machielse, Erik N. Knall, Madison Sutula, Gefen Baranes, Neil Sinclair, Chawina De-Eknamkul, David S. Levonian, Mihir K. Bhaskar, Hongkun Park, Marko Lončar, Mikhail D. Lukin Published: 10.02.2023 Updated: 10.02.2023 Summary A key challenge in realizing practical quantum networks for long-distance quantum communication involves robust entanglement between quantum memory nodes connected via fiber optical infrastructure. Here, we demonstrate a two-node quantum network composed of multi-qubit registers based on silicon-vacancy (SiV) centers in nanophotonic diamond cavities integrated with a telecommunication fiber network. Remote entanglement is generated via the cavity-enhanced interactions between the SiV’s electron spin qubits and optical photons. Serial, heralded spin-photon entangling gate operations with time-bin qubits are used for robust entanglement of separated nodes. Long-lived nuclear spin qubits are used to provide second-long entanglement storage and integrated error detection. By integrating efficient bi-directional quantum frequency conversion of photonic communication qubits to telecommunication frequencies (1350 nm), we demonstrate entanglement of two nuclear spin memories through 40 km spools of low-loss fiber and a 35 km long fiber loop deployed in the Boston area urban environment, representing an enabling step towards practical quantum repeaters and large-scale quantum networks. Source arXiv: 2310.01316v1
SU(d)-Symmetric Random Unitaries: Quantum Scrambling, Error Correction, and Machine Learning Authors Zimu Li, Han Zheng, Yunfei Wang, Liang Jiang, Zi-Wen Liu, Junyu Liu Published: 09.28.2023 Updated: 10.04.2023 Summary Quantum information processing in the presence of continuous symmetry is of wide importance and exhibits many novel physical and mathematical phenomena. SU(d) is a continuous symmetry group of particular interest since it represents a fundamental type of non-Abelian symmetry and also plays a vital role in quantum computation. Here, we explicate the applications of SU(d)-symmetric random unitaries in three different contexts ranging from physics to quantum computing: information scrambling with non-Abelian conserved quantities, covariant quantum error correcting random codes, and geometric quantum machine learning. First, we show that, in the presence of SU(d) symmetry, the local conserved quantities would exhibit residual values even at $t rightarrow infty$ which decays as $Omega(1/n^{3/2})$ under local Pauli basis for qubits and $Omega(1/n^{(d+2)^2/2})$ under local symmetric basis for general qudits with respect to the system size, in contrast to $O(1/n)$ decay for U(1) case and the exponential decay for no-symmetry case in the sense of out-of-time ordered correlator (OTOC). Second, we show that SU(d)-symmetric unitaries can be used to construct asymptotically optimal (in the sense of saturating the fundamental limits on the code error that have been called the approximate Eastin-Knill theorems) SU(d)-covariant codes that encodes any constant $k$ logical qudits, extending [Kong & Liu; PRXQ 3, 020314 (2022)]. Finally, we derive an overpartameterization threshold via the quantum neural tangent kernel (QNTK) required for exponential convergence guarantee of generic ansatz for geometric quantum machine learning, which reveals that the number of parameters required scales only with the dimension of desired subspaces rather than that of the entire Hilbert space. We expect that our work invites further research on quantum information with continuous symmetries. Source arXiv: 2309.16556v2
S-band acoustoelectric amplifier utilizing an ultra-high thermal conductivity heterostructure for low self-heating Authors Lisa Hackett, Xingyu Du, Michael Miller, Brandon Smith, Steven Santillan, Josh Montoya, Robert Reyna, Shawn Arterburn, Scott Weatherrend, Thomas A. Friedmann, Roy H. Olsson III, Matt Eichenfield Published: 09.27.2023 Updated: 09.27.2023 Summary Here we report on an acoustoelectric slab waveguide heterostructure for phonon amplification using a thin Al$_{0.58}$Sc$_{0.42}$N film grown directly on a 4H-SiC substrate with an ultra-thin In$_{0.53}$Ga$_{0.47}$As epitaxial film heterogeneously integrated onto the surface of the Al$_{0.58}$Sc$_{0.42}$N. The aluminum scandium nitride film grown directly on silicon carbide enables a thin (1 micron thick) piezoelectric film to be deposited on a thermally conductive bulk substrate (370 W/m-K for 4H-SiC), enabling negligible self-heating when combined with the In$_{0.53}$Ga$_{0.47}$As semiconductor parameters of large mobility (~7000 cm$^2$/V-s) and low concentration of charge carriers (~5×10$^{15}$ cm$^{-3}$). A Sezawa mode with optimal overlap between the peak of its evanescent electric field and the semiconductor charge carriers is supported. The high velocity of the heterostructure materials allows us to operate the Sezawa mode amplifier at 3.05 GHz, demonstrating a gain of 500 dB/cm (40 dB in 800 microns). Additionally, a terminal end-to-end radio frequency gain of 7.7 dB and a nonreciprocal transmission of 52.6 dB are achieved with a dissipated DC power of 2.3 mW. The power added efficiency and acoustic noise figure are also characterized. Source arXiv: 2309.15725v1
Tight bounds on Pauli channel learning without entanglement Authors Senrui Chen, Changhun Oh, Sisi Zhou, Hsin-Yuan Huang, Liang Jiang Published: 09.23.2023 Updated: 04.17.2024 Summary Quantum entanglement is a crucial resource for learning properties from nature, but a precise characterization of its advantage can be challenging. In this work, we consider learning algorithms without entanglement to be those that only utilize states, measurements, and operations that are separable between the main system of interest and an ancillary system. Interestingly, we show that these algorithms are equivalent to those that apply quantum circuits on the main system interleaved with mid-circuit measurements and classical feedforward. Within this setting, we prove a tight lower bound for Pauli channel learning without entanglement that closes the gap between the best-known upper and lower bound. In particular, we show that $Theta(2^nvarepsilon^{-2})$ rounds of measurements are required to estimate each eigenvalue of an $n$-qubit Pauli channel to $varepsilon$ error with high probability when learning without entanglement. In contrast, a learning algorithm with entanglement only needs $Theta(varepsilon^{-2})$ copies of the Pauli channel. The tight lower bound strengthens the foundation for an experimental demonstration of entanglement-enhanced advantages for Pauli noise characterization. Source arXiv: 2309.13461v2
Tight bounds on Pauli channel learning without entanglement Authors Senrui Chen, Changhun Oh, Sisi Zhou, Hsin-Yuan Huang, Liang Jiang Published: 09.23.2023 Updated: 09.23.2023 Summary Entanglement is a useful resource for learning, but a precise characterization of its advantage can be challenging. In this work, we consider learning algorithms without entanglement to be those that only utilize separable states, measurements, and operations between the main system of interest and an ancillary system. These algorithms are equivalent to those that apply quantum circuits on the main system interleaved with mid-circuit measurements and classical feedforward. We prove a tight lower bound for learning Pauli channels without entanglement that closes a cubic gap between the best-known upper and lower bound. In particular, we show that $Theta(2^nvarepsilon^{-2})$ rounds of measurements are required to estimate each eigenvalue of an $n$-qubit Pauli channel to $varepsilon$ error with high probability when learning without entanglement. In contrast, a learning algorithm with entanglement only needs $Theta(varepsilon^{-2})$ rounds of measurements. The tight lower bound strengthens the foundation for an experimental demonstration of entanglement-enhanced advantages for characterizing Pauli noise. Source arXiv: 2309.13461v1
Optimal entanglement-assisted electromagnetic sensing and communication in the presence of noise Authors Haowei Shi, Bingzhi Zhang, Jeffrey H. Shapiro, Zheshen Zhang, Quntao Zhuang Published: 09.22.2023 Updated: 09.22.2023 Summary High time-bandwidth product signal and idler pulses comprised of independent identically distributed two-mode squeezed vacuum (TMSV) states are readily produced by spontaneous parametric downconversion. These pulses are virtually unique among entangled states in that they offer quantum performance advantages — over their best classical-state competitors — in scenarios whose loss and noise break their initial entanglement. Broadband TMSV states’ quantum advantage derives from its signal and idler having a strongly nonclassical phase-sensitive cross correlation, which leads to information bearing signatures in lossy, noisy scenarios stronger than what can be obtained from classical-state systems of the same transmitted energy. Previous broadband TMSV receiver architectures focused on converting phase-sensitive cross correlation into phase-insensitive cross correlation, which can be measured in second-order interference. In general, however, these receivers fail to deliver broadband TMSV states’ full quantum advantage, even if they are implemented with ideal equipment. This paper introduces the correlation-to-displacement receiver — a new architecture comprised of a correlation-to-displacement converter, a programmable mode selector, and a coherent-state information extractor — that can be configured to achieve quantum optimal performance in known sensing and communication protocols for which broadband TMSV provides quantum advantage that is robust against entanglement-breaking loss and noise. Source arXiv: 2309.12629v1
Efficient multimode Wigner tomography Authors Kevin He, Ming Yuan, Yat Wong, Srivatsan Chakram, Alireza Seif, Liang Jiang, David I. Schuster Published: 09.18.2023 Updated: 09.18.2023 Summary Advancements in quantum system lifetimes and control have enabled the creation of increasingly complex quantum states, such as those on multiple bosonic cavity modes. When characterizing these states, traditional tomography scales exponentially in both computational and experimental measurement requirement, which becomes prohibitive as the state size increases. Here, we implement a state reconstruction method whose sampling requirement instead scales polynomially with subspace size, and thus mode number, for states that can be expressed within such a subspace. We demonstrate this improved scaling with Wigner tomography of multimode entangled W states of up to 4 modes on a 3D circuit quantum electrodynamics (cQED) system. This approach performs similarly in efficiency to existing matrix inversion methods for 2 modes, and demonstrates a noticeable improvement for 3 and 4 modes, with even greater theoretical gains at higher mode numbers. Source arXiv: 2309.10145v1
Integrated Phononic Waveguides in Diamond Authors Sophie Weiyi Ding, Benjamin Pingault, Linbo Shao, Neil Sinclair, Bartholomeus Machielse, Cleaven Chia, Smarak Maity, Marko Lončar Published: 09.15.2023 Updated: 09.15.2023 Summary Efficient generation, guiding, and detection of phonons, or mechanical vibrations, are of interest in various fields including radio frequency communication, sensing, and quantum information. Diamond is an important platform for phononics because of the presence of strain-sensitive spin qubits, and its high Young’s modulus which allows for low-loss gigahertz devices. We demonstrate a diamond phononic waveguide platform for generating, guiding, and detecting gigahertz-frequency surface acoustic wave (SAW) phonons. We generate SAWs using interdigital transducers integrated on AlN/diamond and observe SAW transmission at 4-5 GHz through both ridge and suspended waveguides, with wavelength-scale cross sections (~1 {mu}m2) to maximize spin-phonon interaction. This work is a crucial step for developing acoustic components for quantum phononic circuits with strain-sensitive color centers in diamond. Source arXiv: 2309.08764v1
Designs from Local Random Quantum Circuits with SU(d) Symmetry Authors Zimu Li, Han Zheng, Junyu Liu, Liang Jiang, Zi-Wen Liu Published: 09.15.2023 Updated: 09.15.2023 Summary The convergence of local unitary circuit ensembles to $k$-designs (distributions that emulate the Haar measure up to $k$-th moments) is a central problem in random quantum circuit models which play key roles in the study of quantum information as well as physics. Despite the extensive study of this problem for Haar (completely) random circuits, the crucial situations where symmetries or conservation laws are present remain little understood and are known to pose significant challenges. We propose, for the first time, an explicit local unitary ensemble that is capable of achieving unitary $k$-designs with SU$(d)$ symmetry. To achieve this, we employ the novel Okounkov-Vershik approach to $S_n$ representation theory in quantum physics. We define the Convolutional Quantum Alternating group (CQA) with the corresponding ensemble generated by 4-local SU$(d)$-symmetric unitaries and prove that for all $k < n(n-3)/2$, they form SU$(d)$-symmetric $k$-designs in both exact and approximate ways. We develop a numerical method using the Young orthogonal form and $S_n$ branching rule to study the convergence time of CQA ensemble and provide a strong evidence for nonconstant spectral gap. Then we conjecture a convergence time $Theta(n^4 log(1/epsilon))$ of 1D CQA ensemble to $epsilon$-approximate 2-design in contrast to its counterpart $O(n^2 log (1/epsilon))$ with no symmetry. We also provide comprehensive explanations of the potential difficulties and limitations to analyze the convergence time mathematically through classical methods that worked well for the case without symmetries including local gap threshold, martingale method, and representation theory under SU$(d)$ symmetry, suggesting that a new approach is likely needed to rigorously understand the convergence time of local random circuits with SU$(d)$ symmetry. Source arXiv: 2309.08155v1
Deterministic Creation of Strained Color Centers in Nanostructures via High-Stress Thin Films Authors Daniel R. Assumpcao, Chang Jin, Madison Sutula, Sophie W. Ding, Phong Pham, Can M. Knaut, Mihir K. Bhaskar, Abishrant Panday, Aaron M. Day, Dylan Renaud, Mikhail D. Lukin, Evelyn Hu, Bartholomeus Machielse, Marko Loncar Published: 09.13.2023 Updated: 09.13.2023 Summary Color centers have emerged as a leading qubit candidate for realizing hybrid spin-photon quantum information technology. One major limitation of the platform, however, is that the characteristics of individual color-centers are often strain dependent. As an illustrative case, the silicon-vacancy center in diamond typically requires millikelvin temperatures in order to achieve long coherence properties, but strained silicon vacancy centers have been shown to operate at temperatures beyond 1K without phonon-mediated decoherence. In this work we combine high-stress silicon nitride thin films with diamond nanostructures in order to reproducibly create statically strained silicon-vacancy color centers (mean ground state splitting of 608 GHz) with strain magnitudes of $sim 4 times 10^{-4}$. Based on modeling, this strain should be sufficient to allow for operation of a majority silicon-vacancy centers within the measured sample at elevated temperatures (1.5K) without any degradation of their spin properties. This method offers a scalable approach to fabricate high-temperature operation quantum memories. Beyond silicon-vacancy centers, this method is sufficiently general that it can be easily extended to other platforms as well. Source arXiv: 2309.07935v1
Deterministic Creation of Strained Color Centers in Nanostructures via High-Stress Thin Films Authors Daniel R. Assumpcao, Chang Jin, Madison Sutula, Sophie W. Ding, Phong Pham, Can M. Knaut, Mihir K. Bhaskar, Abishrant Panday, Aaron M. Day, Dylan Renaud, Mikhail D. Lukin, Evelyn Hu, Bartholomeus Machielse, Marko Loncar Published: 09.13.2023 Updated: 11.04.2023 Summary Color centers have emerged as a leading qubit candidate for realizing hybrid spin-photon quantum information technology. One major limitation of the platform, however, is that the characteristics of individual color-centers are often strain dependent. As an illustrative case, the silicon-vacancy center in diamond typically requires millikelvin temperatures in order to achieve long coherence properties, but strained silicon vacancy centers have been shown to operate at temperatures beyond 1K without phonon-mediated decoherence. In this work we combine high-stress silicon nitride thin films with diamond nanostructures in order to reproducibly create statically strained silicon-vacancy color centers (mean ground state splitting of 608 GHz) with strain magnitudes of $sim 4 times 10^{-4}$. Based on modeling, this strain should be sufficient to allow for operation of a majority silicon-vacancy centers within the measured sample at elevated temperatures (1.5K) without any degradation of their spin properties. This method offers a scalable approach to fabricate high-temperature operation quantum memories. Beyond silicon-vacancy centers, this method is sufficiently general that it can be easily extended to other platforms as well. Source arXiv: 2309.07935v2
Quantum Data Center: Perspectives Authors Junyu Liu, Liang Jiang Published: 09.12.2023 Updated: 09.12.2023 Summary A quantum version of data centers might be significant in the quantum era. In this paper, we introduce Quantum Data Center (QDC), a quantum version of existing classical data centers, with a specific emphasis on combining Quantum Random Access Memory (QRAM) and quantum networks. We argue that QDC will provide significant benefits to customers in terms of efficiency, security, and precision, and will be helpful for quantum computing, communication, and sensing. We investigate potential scientific and business opportunities along this novel research direction through hardware realization and possible specific applications. We show the possible impacts of QDCs in business and science, especially the machine learning and big data industries. Source arXiv: 2309.06641v1
Pilot-reference-free continuous-variable quantum key distribution with efficient decoy-state analysis Authors Anran Jin, Xingjian Zhang, Liang Jiang, Richard V. Penty, Pei Zeng Published: 09.07.2023 Updated: 09.07.2023 Summary Continuous-variable quantum key distribution (CV QKD) using optical coherent detectors is practically favorable due to its low implementation cost, flexibility of wavelength division multiplexing, and compatibility with standard coherent communication technologies. However, the security analysis and parameter estimation of CV QKD are complicated due to the infinite-dimensional latent Hilbert space. Also, the transmission of strong reference pulses undermines the security and complicates the experiments. In this work, we tackle these two problems by presenting a time-bin-encoding CV protocol with a simple phase-error-based security analysis valid under general coherent attacks. With the key encoded into the relative intensity between two optical modes, the need for global references is removed. Furthermore, phase randomization can be introduced to decouple the security analysis of different photon-number components. We can hence tag the photon number for each round, effectively estimate the associated privacy using a carefully designed coherent-detection method, and independently extract encryption keys from each component. Simulations manifest that the protocol using multi-photon components increases the key rate by two orders of magnitude compared to the one using only the single-photon component. Meanwhile, the protocol with four-intensity decoy analysis is sufficient to yield tight parameter estimation with a short-distance key-rate performance comparable to the best Bennett-Brassard-1984 implementation. Source arXiv: 2309.03789v1
Quantum Network Planning for Utility Maximization Authors Shahrooz Pouryousef, Hassan Shapourian, Alireza Shabani, Ramana Kompella, Don Towsley Published: 08.30.2023 Updated: 08.30.2023 Summary Existing classical optical network infrastructure cannot be immediately used for quantum network applications due to photon loss. The first step towards enabling quantum networks is the integration of quantum repeaters into optical networks. However, the expenses and intrinsic noise inherent in quantum hardware underscore the need for an efficient deployment strategy that optimizes the allocation of quantum repeaters and memories. In this paper, we present a comprehensive framework for network planning, aiming to efficiently distributing quantum repeaters across existing infrastructure, with the objective of maximizing quantum network utility within an entanglement distribution network. We apply our framework to several cases including a preliminary illustration of a dumbbell network topology and real-world cases of the SURFnet and ESnet. We explore the effect of quantum memory multiplexing within quantum repeaters, as well as the influence of memory coherence time on quantum network utility. We further examine the effects of different fairness assumptions on network planning, uncovering their impacts on real-time network performance. Source arXiv: 2308.16264v1
Resource Allocation for Rate and Fidelity Maximization in Quantum Networks Authors Shahrooz Pouryousef, Hassan Shapourian, Alireza Shabani, Ramana Kompella, Don Towsley Published: 08.30.2023 Updated: 02.08.2024 Summary Existing classical optical network infrastructure cannot be immediately used for quantum network applications due to photon loss. The first step towards enabling quantum networks is the integration of quantum repeaters into optical networks. However, the expenses and intrinsic noise inherent in quantum hardware underscore the need for an efficient deployment strategy that optimizes the allocation of quantum repeaters and memories. In this paper, we present a comprehensive framework for network planning, aiming to efficiently distributing quantum repeaters across existing infrastructure, with the objective of maximizing quantum network utility within an entanglement distribution network. We apply our framework to several cases including a preliminary illustration of a dumbbell network topology and real-world cases of the SURFnet and ESnet. We explore the effect of quantum memory multiplexing within quantum repeaters, as well as the influence of memory coherence time on quantum network utility. We further examine the effects of different fairness assumptions on network planning, uncovering their impacts on real-time network performance. Source arXiv: 2308.16264v2
Entanglement Routing over Networks with Time Multiplexed Repeaters Authors Emily A Van Milligen, Eliana Jacobson, Ashlesha Patil, Gayane Vardoyan, Don Towsley, Saikat Guha Published: 08.29.2023 Updated: 11.15.2023 Summary Quantum networks will be able to service consumers with long distance entanglement by use of repeater nodes that can both generate external Bell pairs with their neighbors, iid with probability $p$, as well as perform internal Bell State Measurements (BSMs) which succeed with some probability $q$. The actual values of these probabilities is dependent upon the experimental parameters of the network in question. While global link state knowledge is needed to maximize the rate of entanglement generation between any two consumers, this may be an unreasonable request due to the dynamic nature of the network. This work evaluates a local link state knowledge, multi-path routing protocol that works with time multiplexed repeaters that are able to perform BSMs across different time steps. This study shows that the average rate increases with the time multiplexing block length, $k$, although the initial latency also increases. When a step function memory decoherence model is introduced so that qubits are held in the quantum memory for a time exponentially distributed with mean $mu$, an optimal $k$ ($k_text{opt}$) value appears. As $p$ decreases or $mu$ increases the value of $k_text{opt}$ increases. This value is such that the benefits from time multiplexing are balanced with the increased risk of losing a previously established entangled pair. Source arXiv: 2308.15028v2