Showing 1–50 of 58 results for author: Wu, T

Sharp Plucker Geometry for Three-Copy Werner Distillation

Authors: Tianhao Wu, Qiran Zou

Abstract: Whether negative-partial-transpose entanglement can remain undistillable is a longstanding problem in quantum information theory. We analyze the first unresolved three-copy Werner endpoint using a sharp dimension-free inequality for complementary partial traces and an optimal exterior-square inequality for orthonormal tripartite vectors. The latter identifies local SWAP- parity statistics with met… ▽ More Whether negative-partial-transpose entanglement can remain undistillable is a longstanding problem in quantum information theory. We analyze the first unresolved three-copy Werner endpoint using a sharp dimension-free inequality for complementary partial traces and an optimal exterior-square inequality for orthonormal tripartite vectors. The latter identifies local SWAP- parity statistics with metric data of a decomposable Plucker bivector. Together these inequalities prove endpoint nonnegativity for every positive semidefinite rank-two coefficient operator and for the complete normal rank-two sector in arbitrary finite local dimensions. For genuinely nonnormal operators, an exact crossed-Gram criterion proves nonnegativity when one local outpu-input support overlap is at most two, including every system with a qubit-sized factor, and when either support plane contains a product ray. Explicit anti-state and rank-boundary families establish optimality of the constants and the rank restriction. △ Less

Submitted 31 July, 2026; originally announced August 2026.

Inverse-squeezing receivers for squeezed-state pulse-position modulation under ideal and phase-diffusion conditions

Authors: Enhao Bai, Fengkai Sun, Tianyi Wu, Huankai Zhang, Jian Peng, Chen Dong, Zhenrong Zhang

Abstract: We introduce a squeezed-state pulse-position modulation (S-PPM) format, where the empty slots are squeezed vacuum states and the pulse slot is a displaced squeezed state. Based on this property, we propose an inverse-squeezing conditional pulse-nulling (IS-CPN) receiver. In the ideal case, inverse squeezing maps S-PPM into an equivalent coherent-state PPM signal with a large pulse energy, leading… ▽ More We introduce a squeezed-state pulse-position modulation (S-PPM) format, where the empty slots are squeezed vacuum states and the pulse slot is a displaced squeezed state. Based on this property, we propose an inverse-squeezing conditional pulse-nulling (IS-CPN) receiver. In the ideal case, inverse squeezing maps S-PPM into an equivalent coherent-state PPM signal with a large pulse energy, leading to a closed-form expression for the receiver error probability. We further analyze IS-CPN under common phase diffusion using a finite-path MAP formulation with phase-averaged likelihoods. Numerical results show that IS-CPN outperforms conventional CPN under the same energy constraint and remains advantageous under phase noise and finite photon-number resolution. These results demonstrate that combining squeezed-state modulation with inverse-squeezing conditional nulling can improve photon-efficient optical communication. △ Less

Submitted 30 June, 2026; originally announced June 2026.

Candidate overtone shear horizontal SAW resonators in thin-film lithium niobate for intermodal acousto-optic modulation

Authors: Wenbing Jiang, Xuankai Xu, Yu Guo, Boyu Zhang, Lihui Jin, Xiao Chen, Tao Wu, Libing Zhou

Abstract: The merits of thin-film surface acoustic wave (SAW) devices are pivotal to develop the high-performance intermodal acousto-optic modulators. In this work, we have proposed shear-horizontal (SH) SAW resonators for anticipated intermodal acousto-optic modulation on the thin-film lithium niobate platform. Through optimization of the cut angle of LN films, the SAW wavelength, and the thickness of inte… ▽ More The merits of thin-film surface acoustic wave (SAW) devices are pivotal to develop the high-performance intermodal acousto-optic modulators. In this work, we have proposed shear-horizontal (SH) SAW resonators for anticipated intermodal acousto-optic modulation on the thin-film lithium niobate platform. Through optimization of the cut angle of LN films, the SAW wavelength, and the thickness of interdigital transducer (IDT) electrodes, the calculated acousto-optic overlap factors utilizing SH0 modes are improved by more than an order of magnitude compared with those of Rayleigh modes. Furthermore, we have fabricated and characterized three kinds of proof-of-principle SH0 mode devices without/with grating reflectors. The electromechanical coupling coefficients (keff^2) and quality factors (Q) in the overtone resonators with grating reflectors are systematically evaluated, featuring the highest Q of 843 with the compromised keff^2 of 0.96%-4.72%. The results reveal that the temperature coefficients of frequency (TCF) of Rayleigh modes vary across various overtones, whereas the SH0 modes exhibit TCFs in the range of 32.3-68.9 ppm/C. Our fabricated SH0-mode overtone resonators demonstrate the capability of operating at power levels up to 29 dBm without electrode damage, offering a promising paradigm for robust and high-efficiency intermodal acousto-optic modulators with potential applications in integrated optical signal processing, microwave photonics,and quantum information technologies. △ Less

Submitted 10 June, 2026; originally announced June 2026.

Comments: 10 pages, 11 figures

Cyclic ladder operators and hidden Weyl-Heisenberg structure in a Floquet system

Authors: Tianao Wu, Li Ge

Abstract: Ladder operators, found in the quantum harmonic oscillator and other quantized systems, provide an elegant approach to solving or understanding otherwise intricate physics problems. In this Letter, we discuss cyclic ladder operators in both Hermitian and non-Hermitian systems with a finite Hilbert space, with the highest (lowest) level directly descending (ascending) to the lowest (highest) level… ▽ More Ladder operators, found in the quantum harmonic oscillator and other quantized systems, provide an elegant approach to solving or understanding otherwise intricate physics problems. In this Letter, we discuss cyclic ladder operators in both Hermitian and non-Hermitian systems with a finite Hilbert space, with the highest (lowest) level directly descending (ascending) to the lowest (highest) level via a single raising (lowering) operation. We show that an equally spaced energy ladder emerges when these systems have an underlying Weyl-Heisenberg commutation relation, with the cyclic ladder operators and the temporal evolution operator behaving as the generators of the Weyl-Heisenberg group. We further illustrate such a system using a one-dimensional Floquet lattice, where the cyclic ladder operators become diagonal and the temporal evolution simplifies to a permutation matrix after a Floquet period. Our findings reveal a hidden relation between non-trivial dynamics and algebraic principles in Floquet systems, which may exist for other quantum numbers as well besides the energy levels. △ Less

Submitted 4 June, 2026; originally announced June 2026.

Comments: 5 pages, 2 figures

Hybrid Classical-Quantum Neural Networks for Multi-Characteristic Co-Optimization of Recessed-Gate AlGaN/GaN MIS-HEMTs

Authors: Rushat Rai, Pei-Jie Chang, Doan Viet Nguyen, Yuan-Chieh Chiu, Niall Tumilty, Yun-Yuan Wang, Simon See, Wen-Jay Lee, Tai-Yue Li, Nan-Yow Chen, Tian-Li Wu

Abstract: Optimizing recessed-gate AlGaN/GaN MIS-HEMTs requires accurate multi-characteristic models, but experimental semiconductor datasets remain costly and encode process-induced variability that simulations cannot faithfully reproduce. This work proposes a hybrid classical-quantum neural network (HQNN) for joint optimization of six electrical targets from a 24-dimensional fabrication/process vector. We… ▽ More Optimizing recessed-gate AlGaN/GaN MIS-HEMTs requires accurate multi-characteristic models, but experimental semiconductor datasets remain costly and encode process-induced variability that simulations cannot faithfully reproduce. This work proposes a hybrid classical-quantum neural network (HQNN) for joint optimization of six electrical targets from a 24-dimensional fabrication/process vector. We systematically screen quantum-circuit templates to extract circuit-design guidance, then select a final HQNN and compare it directly with classical baselines. On 468 experimental fabricated devices spanning 17 process splits, the selected HQNN, Circuit (13, 5) at L = 2, reduces overall normalized root mean square error (nRMSE) by 24.4% relative to ANN. Target-wise, the HQNN lowers Vth,lin RMSE from 0.297 V to 0.270 V, Vth,rev RMSE from 0.278 V to 0.263 V, DeltaVth RMSE from 0.049 V to 0.045 V, SS RMSE from 22.22 mV/dec to 19.87 mV/dec, and Id RMSE from 5.75 x 10^-8 A to 4.35 x 10^-8 A, while Ion RMSE remains competitive (0.053 A vs. 0.056 A). Controlled ansatz ablations further show that performance depends strongly on architecture: parameter count, depth, and two-qubit gate count correlate positively with accuracy, expressibility (DKL) correlates negatively, and controlled-rotation entanglers outperform static controlled-NOT (CNOT)-based circuits in aggregate. A depolarizing-noise study on a representative 4-qubit circuit further suggests that comparable HQNNs may be trainable or deployable on near-term quantum hardware. △ Less

Submitted 19 May, 2026; originally announced May 2026.

Comments: 13 pages, 9 figures

Residual-Squeezing Mechanism of Mismatch in Inverse-Squeezing Kennedy Receivers

Authors: Enhao Bai, Fengkai Sun, Tianyi Wu, Yang Ran, Zichao Zhou, Huankai Zhang, Jian Peng, Chen Dong, Laiyuan Tong, Zhenrong Zhang, Yaping Li

Abstract: The discrimination of quantum states is fundamental to quantum information processing. Inverse-squeezing Kennedy (IS-Kennedy) receivers can outperform the coherent-state BPSK Helstrom benchmark at the same energy by converting transmitter-side squeezing into an effective coherent-state separation gain, without violating the Helstrom bound for the squeezed-state alphabet. This work investigates how… ▽ More The discrimination of quantum states is fundamental to quantum information processing. Inverse-squeezing Kennedy (IS-Kennedy) receivers can outperform the coherent-state BPSK Helstrom benchmark at the same energy by converting transmitter-side squeezing into an effective coherent-state separation gain, without violating the Helstrom bound for the squeezed-state alphabet. This work investigates how squeezing mismatch degrades this mechanism. We show that imperfect inverse squeezing transforms the ideally nulled output into a residually squeezed state, thereby altering the photon-number statistics before detection. This residual-squeezing picture reveals a strong physical asymmetry between squeezing-magnitude and squeezing-phase mismatches. Magnitude mismatch produces an energy-independent error floor in the high-signal-energy regime, whereas phase mismatch generates a residual squeezing term that grows with signal energy. In the small-residual-squeezing regime, this leads to a polynomial growth of the leading error contribution and a rapid collapse of the SQL advantage. We also identify a parity-step effect in photon-number-resolving detection: because the nulled residual squeezed vacuum contains only even photon numbers, increasing detector resolution improves the high-energy robustness only when the effective saturation threshold crosses the next even photon number. These results identify phase locking as the dominant bottleneck for IS-Kennedy-type non-Gaussian receivers under unitary squeezing mismatch and provide design guidelines for robust squeezed-state quantum receivers. △ Less

Submitted 13 August, 2026; v1 submitted 26 January, 2026; originally announced January 2026.

Quantum Recurrent Unit: A Parameter-Efficient Quantum Neural Network Architecture for NISQ Devices

Authors: Tzong-Daw Wu, Hsi-Sheng Goan

Abstract: The rapid growth of modern machine learning (ML) models presents fundamental challenges in parameter efficiency and computational resource requirements. This study introduces the Quantum Recurrent Unit (QRU), a novel quantum neural network (NN) architecture specifically designed to address these challenges while remaining compatible with Noisy Intermediate-Scale Quantum (NISQ) devices. QRU leverag… ▽ More The rapid growth of modern machine learning (ML) models presents fundamental challenges in parameter efficiency and computational resource requirements. This study introduces the Quantum Recurrent Unit (QRU), a novel quantum neural network (NN) architecture specifically designed to address these challenges while remaining compatible with Noisy Intermediate-Scale Quantum (NISQ) devices. QRU leverages quantum controlled-SWAP (C-SWAP; Fredkin) gates to implement an information selection mechanism inspired by classical Gated Recurrent Units (GRUs), enabling selective processing of temporal information via quantum operations. Through its innovative recurrent architecture featuring measurement results feedforward state propagation and shared parameters across time steps, QRU achieves constant circuit depth and constant parameter count regardless of input sequence length, effectively circumventing stringent NISQ hardware constraints. We systematically validate QRU through three progressive experiments: (1) oscillatory behavior prediction, where 72-parameter QRU matches 197-parameter classical GRU performance; (2) Wisconsin Diagnostic Breast Cancer classification, where 35 parameters achieve 96.13% accuracy comparable to 167-parameter artificial NNs; and (3) MNIST handwritten digit recognition, where 132 parameters reach 98.05% accuracy, outperforming a 27,265-parameter convolutional NN. These results demonstrate that QRU consistently achieves comparable or superior performance with significantly fewer parameters than classical NNs while maintaining constant quantum circuit depth. The architecture's quantum-native design, combining C-SWAP-based information selection with novel recurrent processing, suggests QRU's potential as a fundamental building block for next-generation ML systems, offering a promising pathway toward more efficient and scalable quantum ML architectures. △ Less

Submitted 27 January, 2026; v1 submitted 26 January, 2026; originally announced January 2026.

Comments: 32 pages, 10 figures, 8 tables (including supplementary material)

Near-optimal discrimination of displaced squeezed binary signals using displacement, inverse-squeezing, and photon-number-resolving detection

Authors: Enhao bai, Jian Peng, Tianyi Wu, Kai Wen, Fengkai Sun, Chun Zhou, Yaping Li, Zhenrong Zhang, Chen Dong

Abstract: We propose an inverse-squeezing Kennedy receiver for discriminating binary phase-shift-keyed displaced squeezed vacuum states. The receiver combines a Kennedy-type nulling displacement, an orthogonally oriented inverse-squeezing operation and photon-number-resolving detection with a maximum-a-\emph{posteriori} threshold rule. Its key mechanism is that the inverse-squeezing stage converts transmitt… ▽ More We propose an inverse-squeezing Kennedy receiver for discriminating binary phase-shift-keyed displaced squeezed vacuum states. The receiver combines a Kennedy-type nulling displacement, an orthogonally oriented inverse-squeezing operation and photon-number-resolving detection with a maximum-a-\emph{posteriori} threshold rule. Its key mechanism is that the inverse-squeezing stage converts transmitter-side squeezing into enhanced photon-number contrast, or equivalently an effective coherent-state energy gain, that can be directly exploited at the measurement stage. Under ideal equal-prior conditions, the receiver surpasses the standard quantum limit for squeezed-state binary phase-shift keying at approximately $N\approx 0.3$, outperforms the Helstrom bound of coherent-state binary phase-shift keying at approximately $N\approx 0.4$, and reaches the 1\% error level near $N\approx 0.6$. We further analyze its performance under realistic imperfections, including finite detector efficiency, dark counts, channel phase diffusion, receiver thermal noise and transmission loss. The results show that adaptive thresholding preserves robust performance against detector and noise imperfections over practical parameter ranges, whereas transmission loss progressively suppresses the squeezing-enabled advantage. These findings indicate that, for the fixed source parametrization adopted in this work, the proposed receiver is most advantageous in the low-loss regime, especially at low source energies. △ Less

Submitted 11 May, 2026; v1 submitted 13 January, 2026; originally announced January 2026.

Search for a solar-bound axion halo using the Global Network of Optical Magnetometers for Exotic physics searches

Authors: Tatum Z. Wilson, Derek F. Jackson Kimball, Samer Afach, Jiexiao Bi, B. C. Buchler, Dmitry Budker, Kaleb Cervantes, Joshua Eby, Nataniel L. Figueroa, Ron Folman, Jiawei Gao, Daniel Gavilán-Martín, Menachem Givon, Zoran D. Grujić, Hong Guo, Paul Hamilton, M. P. Hedges, Zhejun Huang, Dongok Kim, Younggeun Kim, Sami S. Khamis, Emmanuel Klinger, Abaz Kryemadhi, Nina Kukowski, Jianjun Li , et al. (28 additional authors not shown)

Abstract: We report on a search for a gravitationally bound solar axion halo using data from the Global Network of Optical Magnetometers for Exotic physics searches (GNOME), a worldwide array of magnetically shielded atomic magnetometers with sensitivity to exotic spin couplings. Motivated by recent theoretical work suggesting that self-interacting ultralight axions can be captured by the Sun's gravitationa… ▽ More We report on a search for a gravitationally bound solar axion halo using data from the Global Network of Optical Magnetometers for Exotic physics searches (GNOME), a worldwide array of magnetically shielded atomic magnetometers with sensitivity to exotic spin couplings. Motivated by recent theoretical work suggesting that self-interacting ultralight axions can be captured by the Sun's gravitational field and thermalize into the ground state, we develop a signal model for the pseudo-magnetic fields generated by axion-proton gradient couplings in such a halo. The analysis focuses on the fifth GNOME Science Run (69 days, 12 stations), employing a cross-correlation pipeline with time-shifted daily modulation templates to search for the global, direction-dependent, monochromatic signal expected from a solar axion halo. No statistically significant candidate signals are observed. We set 95% confidence-level upper limits on the amplitude of the axion-induced pseudo-magnetic field over the frequency range $\approx 0.05-20$ Hz, translating to constraints on the linear and quadratic axion-proton couplings for halo densities predicted by gravitational capture models and for the maximum overdensities allowed by planetary ephemerides. In the quadratic coupling case, our limits surpass existing astrophysical bounds by over two orders of magnitude across much of the accessible parameter space. △ Less

Submitted 1 July, 2026; v1 submitted 10 December, 2025; originally announced December 2025.

Comments: 22 pages, 18 figures

Journal ref: Phys. Rev. D 113, 115027 (2026)

Modulation Instability-Induced Multimode Squeezing in Quadratic Frequency Combs

Authors: Haodong Xu, Nianqin Li, Zijun Shu, Yang Shen, Bo Ji, Aiping Xie, Feng Yang, Dengcai Yang, Jing Peng, Hang Gong, Guoxiang Huang, Chunbo Zhao, Wei Li, Tengfei Wu, Guangqiang He

Abstract: Lithium niobate (LN) microring resonators, characterized by an exceptionally high second-order nonlinear coefficient and superior electro-optic tunability, serve as an outstanding platform for the precise control of integrated quantum frequency combs (QFCs). In this study, we introduce a bipartite entanglement criterion to investigate the pairwise entanglement characteristics of QFCs generated via… ▽ More Lithium niobate (LN) microring resonators, characterized by an exceptionally high second-order nonlinear coefficient and superior electro-optic tunability, serve as an outstanding platform for the precise control of integrated quantum frequency combs (QFCs). In this study, we introduce a bipartite entanglement criterion to investigate the pairwise entanglement characteristics of QFCs generated via the spontaneous parametric down-conversion (SPDC) process in lithium niobate microring resonators operating below threshold. Furthermore, we propose a universal framework for analyzing multimode squeezing in quadratic frequency combs, enabling the realization of ultrabroadband and high-degree multimode squeezing. We further reveal the underlying physical mechanism: modulation instability (MI), regulated by temporal walk-off control, not only enables the formation of frequency combs but also induces multimode squeezing in the corresponding resonant modes. This study uncovers the previously unexplored role of on-chip multimode squeezing in quadratic frequency combs while facilitating collective noise suppression across multiple modes, thus holding substantial potential for advancing quantum precision measurement and quantum information processing. △ Less

Submitted 28 August, 2025; originally announced August 2025.

Quantum Tomography in Neutral Meson and Antimeson Systems

Authors: Kun Cheng, Tao Han, Matthew Low, Tong Arthur Wu

Abstract: The flavor space of particles produced in collider environments contains informative quantum correlations. We present a systematic approach for constructing the complete flavor density matrix for a meson and antimeson system ($M \bar M$) in the Bloch vector space at a given time $t$, which can be at or after production. We point out that the $B_s^0$ and $K^0$ systems are superior to the $B^0_d$ an… ▽ More The flavor space of particles produced in collider environments contains informative quantum correlations. We present a systematic approach for constructing the complete flavor density matrix for a meson and antimeson system ($M \bar M$) in the Bloch vector space at a given time $t$, which can be at or after production. We point out that the $B_s^0$ and $K^0$ systems are superior to the $B^0_d$ and $D^0$ systems for quantum tomography because of their flavor oscillation and decay properties. Performing quantum tomography for the $M \bar M$ system can facilitate the study of production mechanisms, decoherence phenomena, quantum information variables, and potential new sources of CP violation. △ Less

Submitted 16 July, 2025; originally announced July 2025.

Comments: 6 pages, 1 figure, 2 tables + supplemental material

Repeated ancilla reuse for logical computation on a neutral atom quantum computer

Authors: J. A. Muniz, D. Crow, H. Kim, J. M. Kindem, W. B. Cairncross, A. Ryou, T. C. Bohdanowicz, C. -A. Chen, Y. Ji, A. M. W. Jones, E. Megidish, C. Nishiguchi, M. Urbanek, L. Wadleigh, T. Wilkason, D. Aasen, K. Barnes, J. M. Bello-Rivas, I. Bloomfield, G. Booth, A. Brown, M. O. Brown, K. Cassella, G. Cowan, J. Epstein , et al. (37 additional authors not shown)

Abstract: Quantum processors based on neutral atoms trapped in arrays of optical tweezers have appealing properties, including relatively easy qubit number scaling and the ability to engineer arbitrary gate connectivity with atom movement. However, these platforms are inherently prone to atom loss, and the ability to replace lost atoms during a quantum computation is an important but previously elusive capa… ▽ More Quantum processors based on neutral atoms trapped in arrays of optical tweezers have appealing properties, including relatively easy qubit number scaling and the ability to engineer arbitrary gate connectivity with atom movement. However, these platforms are inherently prone to atom loss, and the ability to replace lost atoms during a quantum computation is an important but previously elusive capability. Here, we demonstrate the ability to measure and re-initialize, and if necessary replace, a subset of atoms while maintaining coherence in other atoms. This allows us to perform logical circuits that include single and two-qubit gates as well as repeated midcircuit measurement while compensating for atom loss. We highlight this capability by performing up to 41 rounds of syndrome extraction in a repetition code, and combine midcircuit measurement and atom replacement with real-time conditional branching to demonstrate heralded state preparation of a logically encoded Bell state. Finally, we demonstrate the ability to replenish atoms in a tweezer array from an atomic beam while maintaining coherence of existing atoms -- a key step towards execution of logical computations that last longer than the lifetime of an atom in the system. △ Less

Submitted 11 June, 2025; originally announced June 2025.

Comments: 15 pages, 10 figures

Generalization Bounds in Hybrid Quantum-Classical Machine Learning Models

Authors: Tongyan Wu, Amine Bentellis, Alona Sakhnenko, Jeanette Miriam Lorenz

Abstract: Hybrid classical-quantum models aim to harness the strengths of both quantum computing and classical machine learning, but their practical potential remains poorly understood. In this work, we develop a unified mathematical framework for analyzing generalization in hybrid models, offering insight into how these systems learn from data. We establish a novel generalization bound of the form… ▽ More Hybrid classical-quantum models aim to harness the strengths of both quantum computing and classical machine learning, but their practical potential remains poorly understood. In this work, we develop a unified mathematical framework for analyzing generalization in hybrid models, offering insight into how these systems learn from data. We establish a novel generalization bound of the form $\tilde{\mathcal O}\left( \tfrac{α^{k}}{\sqrt{N}}\, \big( k^{\tfrac{3}{2}}\sqrt{m n}\;+\;\sqrt{T\log T}\big) \right)$ for $N$ training data points, $T$ trainable quantum gates, $n$ dimensional quantum circuit output, and $k$ bounded linear layers $ \|F_i\|_F \leq α$ where $ i = 1, \dots, k $ and $F_i \in \mathbb{R}^{m \times n} $ interspersed with activation functions. This generalization bound decomposes into quantum and classical contributions, providing a theoretical framework to separate their influence and clarifying their interaction. Alongside the bound, we highlight conceptual limitations of applying classical statistical learning theory in the hybrid setting and suggest promising directions for future theoretical work. △ Less

Submitted 11 November, 2025; v1 submitted 11 April, 2025; originally announced April 2025.

Comments: Added activation function and multi layer formulations for the generalization bound

Observation of non-Hermitian bulk-boundary correspondence in non-chiral non-unitary quantum dynamics of single photons

Authors: Miao Zhang, Yue Zhang, Shuai Li, Rui Tian, Tianhao Wu, Yingchao Xu, Yi-an Li, Yuanbang Wei, Hong Gao, M. Suhail Zubairy, Fuli Li, Bo Liu

Abstract: The breakdown of conventional bulk-boundary correspondence, a cornerstone of topological physics, is one of counter-intuitive phenomena in non-Hermitian systems, that is deeply rooted in symmetry. In particular, preserved chiral symmetry is one of the key ingredients, which plays a pivotal role in determining non-Hermitian topology. Nevertheless, chiral symmetry breaking in non-Hermitian systems d… ▽ More The breakdown of conventional bulk-boundary correspondence, a cornerstone of topological physics, is one of counter-intuitive phenomena in non-Hermitian systems, that is deeply rooted in symmetry. In particular, preserved chiral symmetry is one of the key ingredients, which plays a pivotal role in determining non-Hermitian topology. Nevertheless, chiral symmetry breaking in non-Hermitian systems disrupts topological protection, modifies topological invariants, and substantially reshapes spectral and edge-state behavior. The corresponding fundamentally important bulk-boundary correspondence thus needs to be drastically reconstructed. However, it has so far eluded experimental efforts. Here, we theoretically predict and experimentally demonstrate the bulk-boundary correspondence of a one-dimensional (1D) non-Hermitian system with chiral symmetry breaking in discrete-time non-chiral non-unitary quantum walks of single photons. Through constructing a domain-wall configuration, we experimentally observe the photon localization at the interface of domain-wall structure, clearly indicating the presence of the topological edge mode. The appearance of that matches excellently with the prediction of our introduced non-chiral non-Bloch topological invariants pair. Our work thus unequivocally builds the non-Hermitian bulk-boundary correspondence as a general principle for studying topological physics in non-Hermitian systems with chiral symmetry breaking. △ Less

Submitted 7 April, 2025; originally announced April 2025.

Comments: 13 pages, 8 figures, including Supplementary Material

Entanglement and Bell Nonlocality in $τ^+ τ^-$ at the LHC using Machine Learning for Neutrino Reconstruction

Authors: Yulei Zhang, Bai-Hong Zhou, Qi-Bin Liu, Tong Arthur Wu, Shu Li, Tao Han, Shih-Chieh Hsu, Matthew Low

Abstract: Experiments at the CERN Large Hadron Collider (LHC) have accumulated an unprecedented amount of data corresponding to a large variety of quantum states. Although searching for new particles beyond the Standard Model of particle physics remains a high priority for the LHC program, precision measurements of the physical processes predicted in the Standard Model continue to lead us to a deeper unders… ▽ More Experiments at the CERN Large Hadron Collider (LHC) have accumulated an unprecedented amount of data corresponding to a large variety of quantum states. Although searching for new particles beyond the Standard Model of particle physics remains a high priority for the LHC program, precision measurements of the physical processes predicted in the Standard Model continue to lead us to a deeper understanding of nature at high energies. We carry out detailed simulations for the process $pp \to τ^+τ^- X$ to perform quantum tomography and to measure the quantum entanglement and the Bell nonlocality of the $τ^+τ^-$ two qubit state, including both statistical and systematic uncertainties. By using advanced machine learning techniques for neutrino momentum reconstruction, we achieve precise measurements of the full spin density matrix, a critical advantage over previous studies limited by reconstruction challenges for missing momenta. Our analysis reveals a clear observation of Bell nonlocality with high statistical significance, surpassing 5$σ$, establishing $τ^+ τ^-$ as an ideal system for quantum information studies in high-energy collisions. Given its experimental feasibility and the high expected sensitivity for Bell nonlocality, we propose that $τ^+ τ^-$ should be regarded as the new benchmark system for quantum information studies at the LHC, complementing and extending the insights gained from the $t\bar{t}$ system. △ Less

Submitted 29 September, 2025; v1 submitted 2 April, 2025; originally announced April 2025.

Journal ref: JHEP04(2026)190

Quantum Information meets High-Energy Physics: Input to the update of the European Strategy for Particle Physics

Authors: Yoav Afik, Federica Fabbri, Matthew Low, Luca Marzola, Juan Antonio Aguilar-Saavedra, Mohammad Mahdi Altakach, Nedaa Alexandra Asbah, Yang Bai, Hannah Banks, Alan J. Barr, Alexander Bernal, Thomas E. Browder, Paweł Caban, J. Alberto Casas, Kun Cheng, Frédéric Déliot, Regina Demina, Antonio Di Domenico, Michał Eckstein, Marco Fabbrichesi, Benjamin Fuks, Emidio Gabrielli, Dorival Gonçalves, Radosław Grabarczyk, Michele Grossi , et al. (46 additional authors not shown)

Abstract: Some of the most astonishing and prominent properties of Quantum Mechanics, such as entanglement and Bell nonlocality, have only been studied extensively in dedicated low-energy laboratory setups. The feasibility of these studies in the high-energy regime explored by particle colliders was only recently shown and has gathered the attention of the scientific community. For the range of particles an… ▽ More Some of the most astonishing and prominent properties of Quantum Mechanics, such as entanglement and Bell nonlocality, have only been studied extensively in dedicated low-energy laboratory setups. The feasibility of these studies in the high-energy regime explored by particle colliders was only recently shown and has gathered the attention of the scientific community. For the range of particles and fundamental interactions involved, particle colliders provide a novel environment where quantum information theory can be probed, with energies exceeding by about 12 orders of magnitude those employed in dedicated laboratory setups. Furthermore, collider detectors have inherent advantages in performing certain quantum information measurements, and allow for the reconstruction of the state of the system under consideration via quantum state tomography. Here, we elaborate on the potential, challenges, and goals of this innovative and rapidly evolving line of research and discuss its expected impact on both quantum information theory and high-energy physics. △ Less

Submitted 8 October, 2025; v1 submitted 31 March, 2025; originally announced April 2025.

Comments: 10 pages, 5 figures

Journal ref: Eur.Phys.J.Plus 140 (2025) 9, 855

Non-Hermiticity enhanced topological immunity of one-dimensional $p$-wave superconducting chain

Authors: Min Liu, Yue Zhang, Rui Tian, Xiayao He, Tianhao Wu, Maksims Arzamasovs, Shuai Li, Bo Liu

Abstract: Studying the immunity of topological superconductors against non-local disorder is one of the key issues in both fundamental researches and potential applications. Here, we demonstrate that the non-Hermiticity can enhance the robustness of topological edge states against non-local disorder. To illustrate that, we consider a one-dimensional (1D) generalized Kitaev model with the asymmetric hopping… ▽ More Studying the immunity of topological superconductors against non-local disorder is one of the key issues in both fundamental researches and potential applications. Here, we demonstrate that the non-Hermiticity can enhance the robustness of topological edge states against non-local disorder. To illustrate that, we consider a one-dimensional (1D) generalized Kitaev model with the asymmetric hopping in the presence of disorder. It is shown that the region supporting Majorana zero modes (MZMs) against non-local disorder will be enlarged by the non-Hermiticity. Through both the numerical and analytical analyses, we show that non-Hermiticity can stabilize the topological superconducting (SC) phase against higher disorder strength. Our studies would offer new insights into the interplay between non-Hermiticity and topology. △ Less

Submitted 9 January, 2025; originally announced January 2025.

Frequency-tunable biphoton generation via spontaneous four-wave mixing

Authors: Jiun-Shiuan Shiu, Chang-Wei Lin, Yu-Chiao Huang, Meng-Jung Lin, I-Chia Huang, Ting-Ho Wu, Pei-Chen Kuan, Yong-Fan Chen

Abstract: We present experimental results on tuning biphoton frequency by introducing a detuned coupling field in spontaneous four-wave mixing (SFWM), and examine its impact on the pairing ratio. This tunability is achieved by manipulating the inherent electromagnetically induced transparency (EIT) effect in the double-$Λ$ scheme. Introducing a detuned coupling field degrades the efficiency of EIT-based sti… ▽ More We present experimental results on tuning biphoton frequency by introducing a detuned coupling field in spontaneous four-wave mixing (SFWM), and examine its impact on the pairing ratio. This tunability is achieved by manipulating the inherent electromagnetically induced transparency (EIT) effect in the double-$Λ$ scheme. Introducing a detuned coupling field degrades the efficiency of EIT-based stimulated four-wave mixing, which in turn reduces the biphoton pairing ratio. However, this reduction can be mitigated by increasing the optical power of the coupling field. Additionally, we observe that blue- and red-detuning the biphoton frequency results in distinct temporal profiles of biphoton wavepackets due to phase mismatch. These findings provide insights into the mechanisms of frequency-tunable biphoton generation via SFWM, and suggest potential optimizations for applications in quantum communication and information processing. △ Less

Submitted 5 December, 2024; originally announced December 2024.

Fault-tolerant quantum computation with a neutral atom processor

Authors: Ben W. Reichardt, Adam Paetznick, David Aasen, Ivan Basov, Juan M. Bello-Rivas, Parsa Bonderson, Rui Chao, Wim van Dam, Matthew B. Hastings, Ryan V. Mishmash, Andres Paz, Marcus P. da Silva, Aarthi Sundaram, Krysta M. Svore, Alexander Vaschillo, Zhenghan Wang, Matt Zanner, William B. Cairncross, Cheng-An Chen, Daniel Crow, Hyosub Kim, Jonathan M. Kindem, Jonathan King, Michael McDonald, Matthew A. Norcia , et al. (47 additional authors not shown)

Abstract: Quantum computing experiments are transitioning from running on physical qubits to using encoded, logical qubits. Fault-tolerant computation can identify and correct errors, and has the potential to enable the dramatically reduced logical error rates required for valuable algorithms. However, it requires flexible control of high-fidelity operations performed on large numbers of qubits. We demonstr… ▽ More Quantum computing experiments are transitioning from running on physical qubits to using encoded, logical qubits. Fault-tolerant computation can identify and correct errors, and has the potential to enable the dramatically reduced logical error rates required for valuable algorithms. However, it requires flexible control of high-fidelity operations performed on large numbers of qubits. We demonstrate fault-tolerant quantum computation on a quantum processor with 256 qubits, each an individual neutral Ytterbium atom. The operations are designed so that key error sources convert to atom loss, which can be detected by imaging. Full connectivity is enabled by atom movement. We demonstrate the entanglement of 24 logical qubits encoded into 48 atoms, at once catching errors and correcting for, on average 1.8, lost atoms. We also implement the Bernstein-Vazirani algorithm with up to 28 logical qubits encoded into 112 atoms, showing better-than-physical error rates. In both cases, "erasure conversion," changing errors into a form that can be detected independently from qubit state, improves circuit performance. These results begin to clear a path for achieving scientific quantum advantage with a programmable neutral atom quantum processor. △ Less

Submitted 9 June, 2025; v1 submitted 18 November, 2024; originally announced November 2024.

Comments: 14 pages, 17 figures

High-fidelity universal gates in the $^{171}$Yb ground state nuclear spin qubit

Authors: J. A. Muniz, M. Stone, D. T. Stack, M. Jaffe, J. M. Kindem, L. Wadleigh, E. Zalys-Geller, X. Zhang, C. -A. Chen, M. A. Norcia, J. Epstein, E. Halperin, F. Hummel, T. Wilkason, M. Li, K. Barnes, P. Battaglino, T. C. Bohdanowicz, G. Booth, A. Brown, M. O. Brown, W. B. Cairncross, K. Cassella, R. Coxe, D. Crow , et al. (28 additional authors not shown)

Abstract: Arrays of optically trapped neutral atoms are a promising architecture for the realization of quantum computers. In order to run increasingly complex algorithms, it is advantageous to demonstrate high-fidelity and flexible gates between long-lived and highly coherent qubit states. In this work, we demonstrate a universal high-fidelity gate-set with individually controlled and parallel application… ▽ More Arrays of optically trapped neutral atoms are a promising architecture for the realization of quantum computers. In order to run increasingly complex algorithms, it is advantageous to demonstrate high-fidelity and flexible gates between long-lived and highly coherent qubit states. In this work, we demonstrate a universal high-fidelity gate-set with individually controlled and parallel application of single-qubit gates and two-qubit gates operating on the ground-state nuclear spin qubit in arrays of tweezer-trapped $^{171}$Yb atoms. We utilize the long lifetime, flexible control, and high physical fidelity of our system to characterize native gates using single and two-qubit Clifford and symmetric subspace randomized benchmarking circuits with more than 200 CZ gates applied to one or two pairs of atoms. We measure our two-qubit entangling gate fidelity to be 99.72(3)% (99.40(3)%) with (without) post-selection. In addition, we introduce a simple and optimized method for calibration of multi-parameter quantum gates. These results represent important milestones towards executing complex and general quantum computation with neutral atoms. △ Less

Submitted 2 December, 2024; v1 submitted 18 November, 2024; originally announced November 2024.

Frequency-dependent squeezing via Einstein-Podolsky-Rosen entanglement based on silicon nitride microring resonators

Authors: Haodong Xu, Zijun Shu, Nianqin Li, Yang Shen, Bo Ji, Yongjun Yang, Tengfei Wu, Mingliang Long, Guangqiang He

Abstract: Significant efforts have been made to enhance the performance of displacement sensors limited by quantum noise, such as gravitational wave detectors. Techniques like frequency-dependent squeezing have overcome the standard quantum limit in optomechanical force measurements, leading to substantial overall progress. These advancements, coupled with major developments in integrated photonics, have pa… ▽ More Significant efforts have been made to enhance the performance of displacement sensors limited by quantum noise, such as gravitational wave detectors. Techniques like frequency-dependent squeezing have overcome the standard quantum limit in optomechanical force measurements, leading to substantial overall progress. These advancements, coupled with major developments in integrated photonics, have paved the way for the emergence of integrated Kerr quantum frequency combs (QFCs). A platform has been established for designing EPR entangled quantum frequency combs using on-chip silicon nitride microring resonators, enabling thorough analysis and optimization of entanglement performance, as well as effective noise reduction adjustments. This platform, incorporating the quantum dynamics of Kerr nonlinear microresonators, supports at least 12 continuous-variable quantum modes in the form of 6 simultaneous two-mode squeezed pairs (EPR entangled pairs). Additionally, by selecting the detection angle of the idler mode, a single-mode squeezed state is generated in the signal mode. Given the frequency-dependent nature of the detection angle, frequency-dependent squeezing is achieved. A comparative analysis of the results under different dispersion conditions is also conducted. △ Less

Submitted 22 October, 2024; v1 submitted 14 September, 2024; originally announced September 2024.

Nonlinearity-induced dynamical self-organized twisted-bilayer lattices in Bose-Einstein condensates

Authors: Rui Tian, Yue Zhang, Tianhao Wu, Min Liu, Yong-Chang Zhang, Shuai Li, Bo Liu

Abstract: Creating crystal bilayers twisted with respect to each other would lead to large periodic supercell structures, which can support a wide range of novel electron correlated phenomena, where the full understanding is still under debate. Here, we propose a new scheme to realize a nonlinearity-induced dynamical self-organized twisted-bilayer lattice in an atomic Bose-Einstein condensate (BEC). The key… ▽ More Creating crystal bilayers twisted with respect to each other would lead to large periodic supercell structures, which can support a wide range of novel electron correlated phenomena, where the full understanding is still under debate. Here, we propose a new scheme to realize a nonlinearity-induced dynamical self-organized twisted-bilayer lattice in an atomic Bose-Einstein condensate (BEC). The key idea here is to utilize the nonlinear effect from the intrinsic atomic interactions to couple different layers and induce a dynamical self-organized supercell structure, dramatically distinct from the conventional wisdom to achieve the static twisted-bilayer lattices. To illustrate that, we study the dynamics of a two-component BEC and show that the nonlinear interaction effect naturally emerged in the Gross-Pitaevskii equation of interacting bosonic ultracold atoms can dynamically induce both periodic (commensurable) and aperiodic (incommensurable) moiré structures. One of the interesting moiré phenomena, i.e., the flat-band physics, is shown through investigating the dynamics of the wave packet of BEC. Our proposal can be implemented using available state-of-the-art experimental techniques and reveal a profound connection between the nonlinearity and twistronics in cold atom quantum simulators. △ Less

Submitted 31 July, 2024; originally announced July 2024.

Comments: 6 pages, 5 figures

A Multi-Messenger Search for Exotic Field Emission with a Global Magnetometer Network

Authors: Sami S. Khamis, Ibrahim A. Sulai, Paul Hamilton, S. Afach, B. C. Buchler, D. Budker, N. L. Figueroa, R. Folman, D. Gavilán-Martín, M. Givon, Z. D. Grujić, H. Guo, M. P. Hedges, D. F. Jackson Kimball, D. Kim, E. Klinger, T. Kornack, A. Kryemadhi, N. Kukowski, G. Lukasiewicz, H. Masia-Roig, M. Padniuk, C. A. Palm, S. Y. Park, X. Peng , et al. (16 additional authors not shown)

Abstract: Quantum sensor networks in combination with traditional astronomical observations are emerging as a novel modality for multi-messenger astronomy. Here we develop a generic analysis framework that uses a data-driven approach to model the sensitivity of a quantum sensor network to astrophysical signals as a consequence of beyond-the-Standard Model (BSM) physics. The analysis method evaluates correla… ▽ More Quantum sensor networks in combination with traditional astronomical observations are emerging as a novel modality for multi-messenger astronomy. Here we develop a generic analysis framework that uses a data-driven approach to model the sensitivity of a quantum sensor network to astrophysical signals as a consequence of beyond-the-Standard Model (BSM) physics. The analysis method evaluates correlations between sensors to search for BSM signals coincident with astrophysical triggers such as black hole mergers, supernovae, or fast radio bursts. Complementary to astroparticle approaches that search for particlelike signals (e.g. WIMPs), quantum sensors are sensitive to wavelike signals from exotic quantum fields. This analysis method can be applied to networks of different types of quantum sensors, such as atomic clocks, matter-wave interferometers, and nuclear clocks, which can probe many types of interactions between BSM fields and standard model particles. We use this analysis method to carry out the first direct search utilizing a terrestrial network of precision quantum sensors for BSM fields emitted during a black hole merger. Specifically we use the Global Network of Optical Magnetometers for Exotic physics (GNOME) to perform a search for exotic low-mass field (ELF) bursts generated in coincidence with a gravitational wave signal from a binary black hole merger (GW200311 115853) detected by LIGO/Virgo on the 11th of March 2020. The associated gravitational wave heralds the arrival of the ELF burst that interacts with the spins of fermions in the magnetometers. This enables GNOME to serve as a tool for multi-messenger astronomy. Our search found no significant events, and consequently we place the first lab-based limits on combinations of ELF production and coupling parameters. △ Less

Submitted 20 May, 2025; v1 submitted 18 July, 2024; originally announced July 2024.

Comments: 23 pages, 12 figures

Journal ref: Phys. Rev. X 15, 031048 (2025)

Simultaneous Generation of Quantum Frequency Combs across Distinct Modal Families in a Single $Si_3 N_4$ Whispering Gallery Mode Resonator

Authors: Bo Ji, Yongjun Yang, Tengfei Wu, Nianqin Li, Guangqiang He

Abstract: Quantum frequency combs (QFCs) are versatile resources for multi-mode entanglement, such as cluster states, crucial for quantum communication and computation. On-chip whispering gallery mode resonators (WGMRs) can generate these states at ultra-low threshold power. This work demonstrates the simultaneous generation of multiple QFCs using a single on-chip silicon nitride WGMR across distinct modal… ▽ More Quantum frequency combs (QFCs) are versatile resources for multi-mode entanglement, such as cluster states, crucial for quantum communication and computation. On-chip whispering gallery mode resonators (WGMRs) can generate these states at ultra-low threshold power. This work demonstrates the simultaneous generation of multiple QFCs using a single on-chip silicon nitride WGMR across distinct modal families. It presents a micro-ring resonator with a radius of 240 $\mathrm{μm}$, capable of supporting four modal families within the 130 to 260 $\mathrm{THz}$ frequency range for consistency regulation. The results indicate that, by carefully designing the structure of silicon nitride WGMRs, it is possible to generate quantum entangled frequency combs across distinct modal families simultaneously using monochromatic pump light. It is achieved by modulating the pump mode profiles with a spatial light modulator (SLM) or an on-chip inverse-designed mode converter. This approach offers a simple and low-cost method to achieve higher-density entanglement integration on-chip. △ Less

Submitted 19 November, 2024; v1 submitted 24 June, 2024; originally announced June 2024.

Comments: 20 pages, 9 figures

Iterative assembly of $^{171}$Yb atom arrays with cavity-enhanced optical lattices

Authors: M. A. Norcia, H. Kim, W. B. Cairncross, M. Stone, A. Ryou, M. Jaffe, M. O. Brown, K. Barnes, P. Battaglino, T. C. Bohdanowicz, A. Brown, K. Cassella, C. -A. Chen, R. Coxe, D. Crow, J. Epstein, C. Griger, E. Halperin, F. Hummel, A. M. W. Jones, J. M. Kindem, J. King, K. Kotru, J. Lauigan, M. Li , et al. (25 additional authors not shown)

Abstract: Assembling and maintaining large arrays of individually addressable atoms is a key requirement for continued scaling of neutral-atom-based quantum computers and simulators. In this work, we demonstrate a new paradigm for assembly of atomic arrays, based on a synergistic combination of optical tweezers and cavity-enhanced optical lattices, and the incremental filling of a target array from a repeti… ▽ More Assembling and maintaining large arrays of individually addressable atoms is a key requirement for continued scaling of neutral-atom-based quantum computers and simulators. In this work, we demonstrate a new paradigm for assembly of atomic arrays, based on a synergistic combination of optical tweezers and cavity-enhanced optical lattices, and the incremental filling of a target array from a repetitively filled reservoir. In this protocol, the tweezers provide microscopic rearrangement of atoms, while the cavity-enhanced lattices enable the creation of large numbers of optical traps with sufficient depth for rapid low-loss imaging of atoms. We apply this protocol to demonstrate near-deterministic filling (99% per-site occupancy) of 1225-site arrays of optical traps. Because the reservoir is repeatedly filled with fresh atoms, the array can be maintained in a filled state indefinitely. We anticipate that this protocol will be compatible with mid-circuit reloading of atoms into a quantum processor, which will be a key capability for running large-scale error-corrected quantum computations whose durations exceed the lifetime of a single atom in the system. △ Less

Submitted 18 June, 2024; v1 submitted 29 January, 2024; originally announced January 2024.

Comments: 8 pages, 6 figures

Exotic Spin-dependent Energy-level Shift Noise Induced by Thermal Motion

Authors: Wei Xiao, Xiyu Liu, Teng Wu, Xiang Peng, Hong Guo

Abstract: Searching for exotic spin-dependent interactions that beyond the standard model has been of interest for past decades and is crucial for unraveling the mysteries of the universe. Previous laboratory searches primarily focus on searching for either static or modulated energy-level shifts caused by exotic spin-dependent interactions. Here, we introduce a theoretical model based on thermal motion of… ▽ More Searching for exotic spin-dependent interactions that beyond the standard model has been of interest for past decades and is crucial for unraveling the mysteries of the universe. Previous laboratory searches primarily focus on searching for either static or modulated energy-level shifts caused by exotic spin-dependent interactions. Here, we introduce a theoretical model based on thermal motion of particles, providing another efficient way to search for exotic spin-dependent interactions. The theoretical model indicates that as the exotic spin-dependent interactions are related with the relative displacements and velocities of atoms, atoms undergoing thermal motion would experience a fluctuating energy-level shift induced by the exotic interactions. Moreover, the resulting exotic energy-level shift noise could be sensed by high-sensitivity instruments. By using the model and taking the high-sensitivity atomic magnetometer as an example, we set the most stringent laboratory experiment constraints on eight different kinds of exotic spin- and velocity-dependent interactions, with five of which at the force range below 1 cm have not been covered previously. Furthermore, this theoretical model can be easily applied in other fields of quantum sensing, such as atomic clocks, atom interferometers and NV-diamond sensors, to further improve the laboratory constraints on exotic spin-dependent interactions. △ Less

Submitted 11 January, 2024; originally announced January 2024.

Temporal bistability in the dissipative Dicke-Bose-Hubbard system

Authors: Tianyi Wu, Sayak Ray, Johann Kroha

Abstract: We consider a driven-dissipative system consisting of an atomic Bose-Einstein condensates loaded into a two-dimensional Hubbard lattice and coupled to a single mode of an optical cavity. Due to the interplay between strong, repulsive atomic interaction and the atom-cavity coupling, the system exhibits several phases of atoms and photons including the atomic superfluid (SF) and supersolid (SS). We… ▽ More We consider a driven-dissipative system consisting of an atomic Bose-Einstein condensates loaded into a two-dimensional Hubbard lattice and coupled to a single mode of an optical cavity. Due to the interplay between strong, repulsive atomic interaction and the atom-cavity coupling, the system exhibits several phases of atoms and photons including the atomic superfluid (SF) and supersolid (SS). We investigate the dynamical behaviour of the system, where we include dissipation by means of Lindblad master equation formalism. Due to the discontinuous nature of the Dicke transition for strong atomic repulsion, we find extended co-existence region of different phases. We investigate the resulting switching dynamics, particularly between the coexisting SF and SS phases, which eventually becomes damped by the dissipation. △ Less

Submitted 28 February, 2024; v1 submitted 22 November, 2023; originally announced November 2023.

Journal ref: Annalen der Physik, 2300505 (2024)

Enhanced Sensitivity in Rydberg Atom Electric Field Sensors through Autler-Townes Effect and Two-Photon Absorption: A Theoretical Analysis Using Many-Mode Floquet Theory

Authors: Tianhao Wu

Abstract: In this paper, we present a comprehensive investigation into the sensitivity of a Rydberg atom electric field sensor, with a specific focus on the minimum detectable field (MDF) as a key metric. The study utilizes one-mode Floquet theory to calculate the Stark shift for selected Rydberg states when exposed to a signal electric field. The results are compared to those obtained using the rotating wa… ▽ More In this paper, we present a comprehensive investigation into the sensitivity of a Rydberg atom electric field sensor, with a specific focus on the minimum detectable field (MDF) as a key metric. The study utilizes one-mode Floquet theory to calculate the Stark shift for selected Rydberg states when exposed to a signal electric field. The results are compared to those obtained using the rotating wave approximation (RWA). To enhance the sensor's sensitivity when the frequency of the signal electric field deviates from resonance frequencies between Rydberg states, we propose incorporating an extra coupling electric field and using many-mode Floquet theory, a generalization of one-mode Floquet theory, to theoretically analyze this kind of Rydberg atom electric field sensor. The Autler-Townes effect resulting from this coupling electric field causes Rydberg states to split into dressed states, effectively increasing sensitivity by modulating the frequencies of resonance peaks. Moreover, the phenomenon of two-photon absorption in the presence of the coupling electric field is explored. We demonstrate that by appropriately adjusting the coupling electric field's amplitude or frequency, one can control the occurrence of two-photon resonances, providing additional sensitivity enhancement for the Rydberg sensor within the significantly extended off-resonance domain. The study underscores the significance of coupling fields in enhancing the sensitivity of Rydberg atom electric field sensors. These insights hold promising implications for the development of more robust and versatile electric field sensing devices, applicable in diverse fields such as precision measurements and quantum information processing. △ Less

Submitted 19 September, 2023; originally announced September 2023.

Mid-circuit qubit measurement and rearrangement in a $^{171}$Yb atomic array

Authors: M. A. Norcia, W. B. Cairncross, K. Barnes, P. Battaglino, A. Brown, M. O. Brown, K. Cassella, C. -A. Chen, R. Coxe, D. Crow, J. Epstein, C. Griger, A. M. W. Jones, H. Kim, J. M. Kindem, J. King, S. S. Kondov, K. Kotru, J. Lauigan, M. Li, M. Lu, E. Megidish, J. Marjanovic, M. McDonald, T. Mittiga , et al. (20 additional authors not shown)

Abstract: Measurement-based quantum error correction relies on the ability to determine the state of a subset of qubits (ancillae) within a processor without revealing or disturbing the state of the remaining qubits. Among neutral-atom based platforms, a scalable, high-fidelity approach to mid-circuit measurement that retains the ancilla qubits in a state suitable for future operations has not yet been demo… ▽ More Measurement-based quantum error correction relies on the ability to determine the state of a subset of qubits (ancillae) within a processor without revealing or disturbing the state of the remaining qubits. Among neutral-atom based platforms, a scalable, high-fidelity approach to mid-circuit measurement that retains the ancilla qubits in a state suitable for future operations has not yet been demonstrated. In this work, we perform imaging using a narrow-linewidth transition in an array of tweezer-confined $^{171}$Yb atoms to demonstrate nondestructive state-selective and site-selective detection. By applying site-specific light shifts, selected atoms within the array can be hidden from imaging light, which allows a subset of qubits to be measured while causing only percent-level errors on the remaining qubits. As a proof-of-principle demonstration of conditional operations based on the results of the mid-circuit measurements, and of our ability to reuse ancilla qubits, we perform conditional refilling of ancilla sites to correct for occasional atom loss, while maintaining the coherence of data qubits. Looking towards true continuous operation, we demonstrate loading of a magneto-optical trap with a minimal degree of qubit decoherence. △ Less

Submitted 2 October, 2023; v1 submitted 30 May, 2023; originally announced May 2023.

Comments: 12 pages, 7 figures

What can a GNOME do? Search targets for the Global Network of Optical Magnetometers for Exotic physics searches

Authors: S. Afach, D. Aybas Tumturk, H. Bekker, B. C. Buchler, D. Budker, K. Cervantes, A. Derevianko, J. Eby, N. L. Figueroa, R. Folman, D. Gavil'an Martin, M. Givon, Z. D. Grujic, H. Guo, P. Hamilton, M. P. Hedges, D. F. Jackson Kimball, S. Khamis, D. Kim, E. Klinger, A. Kryemadhi, X. Liu, G. Lukasiewicz, H. Masia-Roig, M. Padniuk , et al. (28 additional authors not shown)

Abstract: Numerous observations suggest that there exist undiscovered beyond-the-Standard-Model particles and fields. Because of their unknown nature, these exotic particles and fields could interact with Standard Model particles in many different ways and assume a variety of possible configurations. Here we present an overview of the Global Network of Optical Magnetometers for Exotic physics searches (GNOM… ▽ More Numerous observations suggest that there exist undiscovered beyond-the-Standard-Model particles and fields. Because of their unknown nature, these exotic particles and fields could interact with Standard Model particles in many different ways and assume a variety of possible configurations. Here we present an overview of the Global Network of Optical Magnetometers for Exotic physics searches (GNOME), our ongoing experimental program designed to test a wide range of exotic physics scenarios. The GNOME experiment utilizes a worldwide network of shielded atomic magnetometers (and, more recently, comagnetometers) to search for spatially and temporally correlated signals due to torques on atomic spins from exotic fields of astrophysical origin. We survey the temporal characteristics of a variety of possible signals currently under investigation such as those from topological defect dark matter (axion-like particle domain walls), axion-like particle stars, solitons of complex-valued scalar fields (Q-balls), stochastic fluctuations of bosonic dark matter fields, a solar axion-like particle halo, and bursts of ultralight bosonic fields produced by cataclysmic astrophysical events such as binary black hole mergers. △ Less

Submitted 4 May, 2023; v1 submitted 2 May, 2023; originally announced May 2023.

Comments: 22 pages, 12 figures, submitted to Annalen der Physik

Journal ref: Annalen der Physik 2023, 2300083 (2023)

A Multiscale Simulation Approach for Germanium-Hole-Based Quantum Processor

Authors: Tong Wu, Jing Guo

Abstract: A multiscale simulation method is developed to model a quantum dot (QD) array of germanium (Ge) holes for quantum computing. Guided by three-dimensional numerical quantum device simulations of QD structures, an analytical model of the tunnel coupling between the neighboring hole QDs is obtained. Two-qubit entangling quantum gate operations and quantum circuit characteristics of the QD array proces… ▽ More A multiscale simulation method is developed to model a quantum dot (QD) array of germanium (Ge) holes for quantum computing. Guided by three-dimensional numerical quantum device simulations of QD structures, an analytical model of the tunnel coupling between the neighboring hole QDs is obtained. Two-qubit entangling quantum gate operations and quantum circuit characteristics of the QD array processor are then modeled. Device analysis of two-qubit Ge hole quantum gates demonstrates faster gate speed, smaller process variability, and less stringent requirement of feature size, compared to its silicon counterpart. The multiscale simulation method allows assessment of the quantum processor circuit performance from a bottom-up, physics-informed perspective. Application of the simulation method to the Ge QD array processor indicates its promising potential for preparing high-fidelity ansatz states in quantum chemistry simulations. △ Less

Submitted 23 July, 2022; originally announced July 2022.

Comments: 9 pages, 8 figures

Journal ref: IEEE Transactions on Computer-Aided Design of Integrated Circuits and Systems, 2022

State-selective EIT for quantum error correction in neutral atom quantum computers

Authors: Felipe Giraldo Mejia, Aishwarya Kumar, Tsung-Yao Wu, Peng Du, David S. Weiss

Abstract: We propose a way to measure the qubit state of an arbitrary sub-ensemble of atoms in an array without significantly disturbing the quantum information in the unmeasured atoms. The idea is to first site-selectively transfer atoms out of the qubit basis so that one of the two states at a time is put into an auxiliary state. Electromagnetically induced transparency (EIT) light will then protect most… ▽ More We propose a way to measure the qubit state of an arbitrary sub-ensemble of atoms in an array without significantly disturbing the quantum information in the unmeasured atoms. The idea is to first site-selectively transfer atoms out of the qubit basis so that one of the two states at a time is put into an auxiliary state. Electromagnetically induced transparency (EIT) light will then protect most states while detection light is scattered from atoms in the auxiliary state, which is made immune to the EIT protection by angular momentum selection rules and carefully chosen light polarization. The two states will be measured in turn, after which it is possible to recool and return the atoms to a qubit state. These measurements can be the basis of quantum error correction. △ Less

Submitted 3 May, 2022; originally announced May 2022.

Comments: 14 pages, 16 figures

Normalization, orthogonality and completeness of quasinormal modes of open systems: the case of electromagnetism

Authors: C. Sauvan, T. Wu, R. Zarouf, E. A. Muljarov, P. Lalanne

Abstract: The scattering of electromagnetic waves by resonant systems is determined by the excitation of quasinormal modes (QNMs), i.e., the eigenmodes of the system. This Review addresses three fundamental concepts in relation with the representation of the scattered field as a superposition of the excited QNMs: normalization, orthogonality, and completeness. Orthogonality and normalization enable a straig… ▽ More The scattering of electromagnetic waves by resonant systems is determined by the excitation of quasinormal modes (QNMs), i.e., the eigenmodes of the system. This Review addresses three fundamental concepts in relation with the representation of the scattered field as a superposition of the excited QNMs: normalization, orthogonality, and completeness. Orthogonality and normalization enable a straightforward assessment of the QNM excitation strength for any incident wave. Completeness guaranties that the scattered field can be faithfully expanded into the QNM basis. These concepts are non-trivial for non-conservative (non-Hermitian) systems and have driven many theoretical developments since initial studies in the 70's. Yet, owing to recent achievements, they are not easily grasped from the extensive and scattered literature, especially for newcomers in the field. After recalling fundamental results obtained in early studies on the completeness of the QNM basis for simple resonant systems, we review recent achievements and debates on the normalization, clarify under which circumstances the QNM basis is complete, and highlight the concept of QNM regularization with complex coordinate transform. △ Less

Submitted 15 December, 2021; originally announced December 2021.

Learning Interpretable Representations of Entanglement in Quantum Optics Experiments using Deep Generative Models

Authors: Daniel Flam-Shepherd, Tony Wu, Xuemei Gu, Alba Cervera-Lierta, Mario Krenn, Alan Aspuru-Guzik

Abstract: Quantum physics experiments produce interesting phenomena such as interference or entanglement, which are core properties of numerous future quantum technologies. The complex relationship between the setup structure of a quantum experiment and its entanglement properties is essential to fundamental research in quantum optics but is difficult to intuitively understand. We present a deep generative… ▽ More Quantum physics experiments produce interesting phenomena such as interference or entanglement, which are core properties of numerous future quantum technologies. The complex relationship between the setup structure of a quantum experiment and its entanglement properties is essential to fundamental research in quantum optics but is difficult to intuitively understand. We present a deep generative model of quantum optics experiments where a variational autoencoder is trained on a dataset of quantum optics experimental setups. In a series of computational experiments, we investigate the learned representation of our Quantum Optics Variational Auto Encoder (QOVAE) and its internal understanding of the quantum optics world. We demonstrate that the QOVAE learns an interpretable representation of quantum optics experiments and the relationship between experiment structure and entanglement. We show the QOVAE is able to generate novel experiments for highly entangled quantum states with specific distributions that match its training data. The QOVAE can learn to generate specific entangled states and efficiently search the space of experiments that produce highly entangled quantum states. Importantly, we are able to interpret how the QOVAE structures its latent space, finding curious patterns that we can explain in terms of quantum physics. The results demonstrate how we can use and understand the internal representations of deep generative models in a complex scientific domain. The QOVAE and the insights from our investigations can be immediately applied to other physical systems. △ Less

Submitted 16 June, 2022; v1 submitted 6 September, 2021; originally announced September 2021.

Comments: Published in Nature Machine Intelligence https://doi.org/10.1038/s42256-022-00493-5

Journal ref: Nature Machine Intelligence 4, 544 (2022)

Assembly and coherent control of a register of nuclear spin qubits

Authors: Katrina Barnes, Peter Battaglino, Benjamin J. Bloom, Kayleigh Cassella, Robin Coxe, Nicole Crisosto, Jonathan P. King, Stanimir S. Kondov, Krish Kotru, Stuart C. Larsen, Joseph Lauigan, Brian J. Lester, Mickey McDonald, Eli Megidish, Sandeep Narayanaswami, Ciro Nishiguchi, Remy Notermans, Lucas S. Peng, Albert Ryou, Tsung-Yao Wu, Michael Yarwood

Abstract: We introduce an optical tweezer platform for assembling and individually manipulating a two-dimensional register of nuclear spin qubits. Each nuclear spin qubit is encoded in the ground $^{1}S_{0}$ manifold of $^{87}$Sr and is individually manipulated by site-selective addressing beams. We observe that spin relaxation is negligible after 5 seconds, indicating that $T_1\gg5$ s. Furthermore, utilizi… ▽ More We introduce an optical tweezer platform for assembling and individually manipulating a two-dimensional register of nuclear spin qubits. Each nuclear spin qubit is encoded in the ground $^{1}S_{0}$ manifold of $^{87}$Sr and is individually manipulated by site-selective addressing beams. We observe that spin relaxation is negligible after 5 seconds, indicating that $T_1\gg5$ s. Furthermore, utilizing simultaneous manipulation of subsets of qubits, we demonstrate significant phase coherence over the entire register, estimating $T_2^\star = \left(21\pm7\right)$ s and measuring $T_2^\text{echo}=\left(42\pm6\right)$ s. △ Less

Submitted 10 August, 2021; originally announced August 2021.

Comments: 10 pages, 4 figures

Machine-Learning-Derived Entanglement Witnesses

Authors: Alexander C. B. Greenwood, Larry T. H. Wu, Eric Y. Zhu, Brian T. Kirby, Li Qian

Abstract: In this work, we show a correspondence between linear support vector machines (SVMs) and entanglement witnesses, and use this correspondence to generate entanglement witnesses for bipartite and tripartite qubit (and qudit) target entangled states. An SVM allows for the construction of a hyperplane that clearly delineates between separable states and the target entangled state; this hyperplane is a… ▽ More In this work, we show a correspondence between linear support vector machines (SVMs) and entanglement witnesses, and use this correspondence to generate entanglement witnesses for bipartite and tripartite qubit (and qudit) target entangled states. An SVM allows for the construction of a hyperplane that clearly delineates between separable states and the target entangled state; this hyperplane is a weighted sum of observables ('features') whose coefficients are optimized during the training of the SVM. We demonstrate with this method the ability to obtain witnesses that require only local measurements even when the target state is a non-stabilizer state. Furthermore, we show that SVMs are flexible enough to allow us to rank features, and to reduce the number of features systematically while bounding the inference error. This allows us to derive W state witnesses capable of detecting entanglement with fewer measurement terms than the fidelity method dominant in today's literature. The utility of this approach is demonstrated on quantum hardware furnished through the IBM Quantum Experience. △ Less

Submitted 22 March, 2023; v1 submitted 5 July, 2021; originally announced July 2021.

Comments: 11 pages

Journal ref: Phys. Rev. Applied 19, 034058 (2023)

Exploiting potentialities for space-based quantum communication network: downlink quantum key distribution modelling and scheduling analysis

Authors: Xingyu Wang, Chen Dong, Jiahua Wei, Tianyi Wu, Taoyong Li, Huicun Yu, Lei Shi, Shanghong Zhao

Abstract: With the goal of a space-based quantum network is to have satellites distribute keys between any nodes on the ground, we consider an evolved quantum network from a near-term form, in which a space-based relay, satellite executes a sequence of satellite-based quantum key distribution (SatQKD) missions, allowing any two ground nodes to have a shared secure key. Accordingly, we develop a comprehensiv… ▽ More With the goal of a space-based quantum network is to have satellites distribute keys between any nodes on the ground, we consider an evolved quantum network from a near-term form, in which a space-based relay, satellite executes a sequence of satellite-based quantum key distribution (SatQKD) missions, allowing any two ground nodes to have a shared secure key. Accordingly, we develop a comprehensive framework for the dynamic simulation of SatQKD and consider scheduling QKD downlink in future space-based quantum communication network. The embedding of precise orbital model including beam diffractions and atmosphere effects makes our framework more realistic. Incorporated with the local meteorological data to channel loss model, the cloud cover contribution to transmission disturbance is quantified to realize a quasi-experimental scenario. We provide a trade-off consideration between the duration available for communications and its corresponding average link loss during one orbit, which could be used to support decisions involving the locations of ground stations and the selection of the orbital parameters for a quantum satellite. Our work also shows that satellite downlink schedule could allow for the possibility to consider strategies for different SatQKD missions such as extending connection for distant ground nodes, prioritized delivery, or promoting keys utilization, which can be used as a guideline to support decisions for future satellite application. △ Less

Submitted 9 October, 2022; v1 submitted 2 June, 2021; originally announced June 2021.

Comments: Comments welcome!

Lens-free Optical Detection of Thermal Motion of a Sub-millimeter Sphere Diamagnetically Levitated in High Vacuum

Authors: Fang Xiong, Peiran Yin, Tong Wu, Han Xie, Rui Li, Yingchun Leng, Yanan Li, Changkui Duan, Xi Kong, Pu Huang, Jiangfeng Du

Abstract: Levitated oscillators with millimeter or sub-millimeter size are particularly attractive due to their potential role in studying various fundamental problems and practical applications. One of the crucial issues towards these goals is to achieve efficient measurements of oscillator motion, while this remains a challenge. Here we theoretically propose a lens-free optical detection scheme, which can… ▽ More Levitated oscillators with millimeter or sub-millimeter size are particularly attractive due to their potential role in studying various fundamental problems and practical applications. One of the crucial issues towards these goals is to achieve efficient measurements of oscillator motion, while this remains a challenge. Here we theoretically propose a lens-free optical detection scheme, which can be used to detect the motion of a millimeter or sub-millimeter levitated oscillator with a measurement efficiency close to the standard quantum limit with a modest optical power. We demonstrate experimentally this scheme on a 0.5 mm diameter micro-sphere that is diamagnetically levitated under high vacuum and room temperature, and the thermal motion is detected with high precision. Based on this system, an estimated acceleration sensitivity of $9.7 \times 10^{-10}\rm g/\sqrt{Hz}$ is achieved, which is more than one order improvement over the best value reported by the levitated mechanical system. Due to the stability of the system, the minimum resolved acceleration of $3.5\times 10^{-12}\rm g$ is reached with measurement times of $10^5$ s. This result is expected to have potential applications in the study of exotic interactions in the millimeter or sub-millimeter range and the realization of compact gravimeter and accelerometer. △ Less

Submitted 27 May, 2021; originally announced May 2021.

Comments: Physical Review Applied (to be published)

Journal ref: Phys. Rev. Applied 16, 011003 (2021)

A compressive sensing based parameter estimation for free space continuous variable quantum key distribution

Authors: Xiaowen Liu, Chen Dong, Xingyu Wang, Tianyi Wu

Abstract: In satellite-based free-space continuous-variable QKD (CV-QKD), the parameter estimation for the atmospheric channel fluctuations due to the turbulence effects and attenuation is crucial for analyzing and improving the protocol performance. In this paper, compressive sensing (CS) theory is applied to free-space CV-QKD to achieve the channel parameter estimation with low computational complexity an… ▽ More In satellite-based free-space continuous-variable QKD (CV-QKD), the parameter estimation for the atmospheric channel fluctuations due to the turbulence effects and attenuation is crucial for analyzing and improving the protocol performance. In this paper, compressive sensing (CS) theory is applied to free-space CV-QKD to achieve the channel parameter estimation with low computational complexity and small amount of data. According to CS theory, the possibility of the sparse representation for free-space channel is analyzed and the two types of sparse reconstruction models for the channel parameters are constructed combining with the stability of the sub-channels. The most part of variable for parameter estimation is saved by using the model relying on the variables in the quantum signals, while all the variables can be used to generate the secret key by using the model relying on the second-order statistics of the variables. The methods are well adapted for the cases with the limited communication time since a little or no variable is sacrificed for parameter estimation. Finally, simulation results are given to verify the effectiveness of the proposed methods. △ Less

Submitted 25 March, 2021; originally announced March 2021.

Comments: 11 pages, 6 figures

Variability and Fidelity Limits of Silicon Quantum Gates Due to Random Interface Charge Traps

Authors: Tong Wu, Jing Guo

Abstract: Silicon offers an attractive material platform for hardware realization of quantum computing. In this study, a microscopic stochastic simulation method is developed to model the effect of random interface charge traps in silicon metal-oxide-semiconductor (MOS) quantum gates. The statistical results show that by using a fast two-qubit gate in isotopically purified silicon, the two-qubit silicon-bas… ▽ More Silicon offers an attractive material platform for hardware realization of quantum computing. In this study, a microscopic stochastic simulation method is developed to model the effect of random interface charge traps in silicon metal-oxide-semiconductor (MOS) quantum gates. The statistical results show that by using a fast two-qubit gate in isotopically purified silicon, the two-qubit silicon-based quantum gates have the fidelity >98% with a probability of 75% for the state-of-the-art MOS interface quality. By using a composite gate pulse, the fidelity can be further improved to >99.5% with the 75% probability. The variations between the quantum gate devices, however, are largely due to the small number of traps per device. The results highlight the importance of variability consideration due to random charge traps and potential to improve fidelity in silicon-based quantum computing. △ Less

Submitted 10 November, 2020; originally announced November 2020.

Comments: 4 pages, 5 figures. IEEE Electron Device Letters (2020)

Searching spin-mass interaction using a diamagnetic levitated magnetic resonance force sensor

Authors: Fang Xiong, Tong Wu, Yingchun Leng, Rui Li, Changkui Duan, Xi Kong, Pu Huang, Zhengwei Li, Yu Gao, Xing Rong, Jiangfeng Du

Abstract: Axion-like particles (ALPs) are predicted to mediate exotic interactions between spin and mass. We propose an ALP-searching experiment based on the levitated micromechanical oscillator, which is one of the most sensitive sensors for spin-mass forces at a short distance. The proposed experiment tests the spin-mass resonant interaction between the polarized electron spins and a diamagnetically levit… ▽ More Axion-like particles (ALPs) are predicted to mediate exotic interactions between spin and mass. We propose an ALP-searching experiment based on the levitated micromechanical oscillator, which is one of the most sensitive sensors for spin-mass forces at a short distance. The proposed experiment tests the spin-mass resonant interaction between the polarized electron spins and a diamagnetically levitated microsphere. By periodically flipping the electron spins, the contamination from nonresonant background forces can be eliminated. The levitated microoscillator can prospectively enhance the sensitivity by nearly $10^3$ times over current experiments for ALPs with mass in the range 4 meV to 0.4 eV. △ Less

Submitted 7 March, 2021; v1 submitted 27 October, 2020; originally announced October 2020.

Comments: 11 pages, 8 figures

Journal ref: Phys. Rev. Research 3, 013205 (2021)

Mechanical dissipation below 1$μ$Hz with a cryogenic diamagnetic-levitated micro-oscillator

Authors: Yingchun Leng, Rui Li, Xi Kong, Han Xie, Di Zheng, Peiran Yin, Fang Xiong, Tong Wu, Chang Kui Duan, Youwei Du, Zhang qi Yin, Pu Huang, Jiangfeng Du

Abstract: Ultralow dissipation plays an important role in sensing applications and exploring macroscopic quantum phenomena using micro-and nano-mechanical systems. We report a diamagnetic-levitated micro-mechanical oscillator operating at a low temperature of 3K with measured dissipation as low as 0.59 $μ$Hz and a quality factor as high as $2 \times 10^7$. To the best of our knowledge the achieved dissipati… ▽ More Ultralow dissipation plays an important role in sensing applications and exploring macroscopic quantum phenomena using micro-and nano-mechanical systems. We report a diamagnetic-levitated micro-mechanical oscillator operating at a low temperature of 3K with measured dissipation as low as 0.59 $μ$Hz and a quality factor as high as $2 \times 10^7$. To the best of our knowledge the achieved dissipation is the lowest in micro- and nano-mechanical systems to date, orders of magnitude improvement over the reported state-of-the-art systems based on different principles. The cryogenic diamagnetic-levitated oscillator described here is applicable to a wide range of mass, making it a good candidate for measuring both force and acceleration with ultra-high sensitivity. By virtue of the naturally existing strong magnetic gradient, this system has great potential in quantum spin mechanics study. △ Less

Submitted 18 August, 2020; v1 submitted 18 August, 2020; originally announced August 2020.

Comments: 6 pages, 3 figures

Journal ref: Phys. Rev. Applied 15, 024061 (2021)

Experimental parity-time symmetry quantum walks on a directed graph

Authors: Tong Wu, J. A. Izaac, Zi-Xi Li, Kai Wang, Zhao-Zhong Chen, Shining Zhu, J. B. Wang, Xiao-Song Ma

Abstract: Quantum walks (QW) are of crucial importance in the development of quantum information processing algorithms. Recently, several quantum algorithms have been proposed to implement network analysis, in particular to rank the centrality of nodes in networks represented by graphs. Employing QW in centrality ranking is advantageous comparing to certain widely used classical algorithms (e.g. PageRank) b… ▽ More Quantum walks (QW) are of crucial importance in the development of quantum information processing algorithms. Recently, several quantum algorithms have been proposed to implement network analysis, in particular to rank the centrality of nodes in networks represented by graphs. Employing QW in centrality ranking is advantageous comparing to certain widely used classical algorithms (e.g. PageRank) because QW approach can lift the vertex rank degeneracy in certain graphs. However, it is challenging to implement a directed graph via QW, since it corresponds to a non-Hermitian Hamiltonian and thus cannot be accomplished by conventional QW. Here we report the realizations of centrality rankings of both a three-vertex and four-vertex directed graphs with parity-time (PT) symmetric quantum walks. To achieve this, we use high-dimensional photonic quantum states, optical circuitries consisting of multiple concatenated interferometers and dimension dependent loss. Importantly, we demonstrate the advantage of QW approach experimentally by breaking the vertex rank degeneracy in a four-vertex graph. Our work shows that PT-symmetric quantum walks may be useful for realizing advanced algorithm in a quantum network. △ Less

Submitted 18 December, 2019; originally announced December 2019.

Journal ref: Phys. Rev. Lett. 125, 240501 (2020)

High mobility InAs 2DEGs on GaSb substrates: a platform for mesoscopic quantum transport

Authors: C. Thomas, A. T. Hatke, A. Tuaz, R. Kallaher, T. Wu, T. Wang, R. E. Diaz, G. C. Gardner, M. A. Capano, M. J. Manfra

Abstract: High mobility, strong spin-orbit coupling, and large Landé g-factor make the two-dimensional electron gas (2DEG) in InAs quantum wells grown on nearly-lattice-matched GaSb substrates an attractive platform for mesoscopic quantum transport experiments. Successful operation of mesoscopic devices relies on three key properties: electrical isolation from the substrate; ability to fully deplete the 2DE… ▽ More High mobility, strong spin-orbit coupling, and large Landé g-factor make the two-dimensional electron gas (2DEG) in InAs quantum wells grown on nearly-lattice-matched GaSb substrates an attractive platform for mesoscopic quantum transport experiments. Successful operation of mesoscopic devices relies on three key properties: electrical isolation from the substrate; ability to fully deplete the 2DEG and control residual sidewall conduction with lithographic gates; and high mobility to ensure ballistic transport over mesoscopic length scales. Simultaneous demonstration of these properties has remained elusive for InAs 2DEGs on GaSb substrates. Here we report on heterostructure design, molecular beam epitaxy growth, and device fabrication that result in high carrier mobility and full 2DEG depletion with minimal residual edge conduction. Our results provide a pathway to fully-controlled 2DEG-based InAs mesoscopic devices. △ Less

Submitted 27 July, 2018; originally announced July 2018.

Comments: 5 figures

Journal ref: Phys. Rev. Materials 2, 104602 (2018)

Multifrequency multi-qubit entanglement based on plasmonic hot spots

Authors: Jun Ren, Tong Wu, Xiangdong Zhang

Abstract: The theoretical method to study strong coupling between an ensemble of quantum emitters (QEs) and surface plasmons excited by the nanoparticle cluster has been presented by using a rigorous first-principles electromagnetic Green's tensor technique. We have demonstrated that multi-qubit entanglement for two-level QEs can be produced at different frequencies simultaneously, when they locate in hot s… ▽ More The theoretical method to study strong coupling between an ensemble of quantum emitters (QEs) and surface plasmons excited by the nanoparticle cluster has been presented by using a rigorous first-principles electromagnetic Green's tensor technique. We have demonstrated that multi-qubit entanglement for two-level QEs can be produced at different frequencies simultaneously, when they locate in hot spots of metallic nanoparticle clusters. The duration of quantum beats for such an entanglement can reach two orders longer than that for the entanglement in a photonic cavity. The phenomenon originates from collective coupling resonance excitation of the cluster. At the frequency of single scattering resonance, the entanglement cannot be produced although the single QE spontaneous decay rate is very big △ Less

Submitted 27 December, 2017; originally announced December 2017.

Journal ref: Scientific Report 2015

Experimental Benchmarking of Quantum Control in Zero-Field Nuclear Magnetic Resonance

Authors: Min Jiang, Teng Wu, John W. Blanchard, Guanru Feng, Xinhua Peng, Dmitry Budker

Abstract: Zero-field nuclear magnetic resonance (NMR) provides complementary analysis modalities to those of high-field NMR and allows for ultra-high-resolution spectroscopy and measurement of untruncated spin-spin interactions. Unlike for the high-field case, however, universal quantum control -- the ability to perform arbitrary unitary operations -- has not been experimentally demonstrated in zero-field N… ▽ More Zero-field nuclear magnetic resonance (NMR) provides complementary analysis modalities to those of high-field NMR and allows for ultra-high-resolution spectroscopy and measurement of untruncated spin-spin interactions. Unlike for the high-field case, however, universal quantum control -- the ability to perform arbitrary unitary operations -- has not been experimentally demonstrated in zero-field NMR. This is because the Larmor frequency for all spins is identically zero at zero field, making it challenging to individually address different spin species. We realize a composite-pulse technique for arbitrary independent rotations of $^1$H and $^{13}$C spins in a two-spin system. Quantum-information-inspired randomized benchmarking and state tomography are used to evaluate the quality of the control. We experimentally demonstrate single-spin control for $^{13}$C with an average gate fidelity of $0.9960(2)$ and two-spin control via a controlled-not (CNOT) gate with an estimated fidelity of $0.99$. The combination of arbitrary single-spin gates and a CNOT gate is sufficient for universal quantum control of the nuclear spin system. The realization of complete spin control in zero-field NMR is an essential step towards applications to quantum simulation, entangled-state-assisted quantum metrology, and zero-field NMR spectroscopy. △ Less

Submitted 21 August, 2017; originally announced August 2017.

Comments: 19 pages, 3 figures

Journal ref: Science advances. 2018 Jun 15;4(6):eaar6327

Bright Single Photons for Light Matter Interaction

Authors: Chih-Hsiang Wu, Tsung-Yao Wu, Yung-Chin Yeh, Po-Hui Liu, Chin-Hsuan Chang, Chiao-Kai Liu, Ting Cheng, Chih-Sung Chuu

Abstract: Single photons of subnatural linewidth and high spectral brightness are necessary for efficient light-matter interaction at the single photon level, which lies at the heart of many quantum photonic technologies. Here we demonstrate a bright source of single photons with subnatural linewidth, controllable waveforms, and a high spectral brightness of $3.67 \times 10^5$ s$^{-1}$mW$^{-1}$MHz$^{-1}$. T… ▽ More Single photons of subnatural linewidth and high spectral brightness are necessary for efficient light-matter interaction at the single photon level, which lies at the heart of many quantum photonic technologies. Here we demonstrate a bright source of single photons with subnatural linewidth, controllable waveforms, and a high spectral brightness of $3.67 \times 10^5$ s$^{-1}$mW$^{-1}$MHz$^{-1}$. The interaction between the single photons and atoms is demonstrated by the controlled absorption of the single photons in an atomic vapor. Our work has potential applications in quantum information technologies. △ Less

Submitted 7 August, 2017; originally announced August 2017.

Comments: 5 pages, 4 figures

Journal ref: Phys. Rev. A 96, 023811 (2017)

The Cosmic Axion Spin Precession Experiment (CASPEr): a dark-matter search with nuclear magnetic resonance

Authors: Antoine Garcon, Deniz Aybas, John W. Blanchard, Gary Centers, Nataniel L. Figueroa, Peter W. Graham, Derek F. Jackson Kimball, Surjeet Rajendran, Marina Gil Sendra, Alexander O. Sushkov, Lutz Trahms, Tao Wang, Arne Wickenbrock, Teng Wu, Dmitry Budker

Abstract: The Cosmic Axion Spin Precession Experiment (CASPEr) is a nuclear magnetic resonance experiment (NMR) seeking to detect axion and axion-like particles which could make up the dark matter present in the universe. We review the predicted couplings of axions and axion-like particles with baryonic matter that enable their detection via NMR. We then describe two measurement schemes being implemented in… ▽ More The Cosmic Axion Spin Precession Experiment (CASPEr) is a nuclear magnetic resonance experiment (NMR) seeking to detect axion and axion-like particles which could make up the dark matter present in the universe. We review the predicted couplings of axions and axion-like particles with baryonic matter that enable their detection via NMR. We then describe two measurement schemes being implemented in CASPEr. The first method, presented in the original CASPEr proposal, consists of a resonant search via continuous-wave NMR spectroscopy. This method offers the highest sensitivity for frequencies ranging from a few Hz to hundreds of MHz, corresponding to masses $ m_{\rm a} \sim 10^{-14}$--$10^{-6}$ eV. Sub-Hz frequencies are typically difficult to probe with NMR due to the diminishing sensitivity of magnetometers in this region. To circumvent this limitation, we suggest new detection and data processing modalities. We describe a non-resonant frequency-modulation detection scheme, enabling searches from mHz to Hz frequencies ($m_{\rm a} \sim 10^{-17}$--$10^{-14} $ eV), extending the detection bandwidth by three decades. △ Less

Submitted 17 October, 2017; v1 submitted 16 July, 2017; originally announced July 2017.

Journal ref: Quantum Science and Technology 2017

Miniature cavity-enhanced diamond magnetometer

Authors: Georgios Chatzidrosos, Arne Wickenbrock, Lykourgos Bougas, Nathan Leefer, Teng Wu, Kasper Jensen, Yannick Dumeige, Dmitry Budker

Abstract: We present a highly sensitive miniaturized cavity-enhanced room-temperature magnetic-field sensor based on nitrogen-vacancy (NV) centers in diamond. The magnetic resonance signal is detected by probing absorption on the 1042\,nm spin-singlet transition. To improve the absorptive signal the diamond is placed in an optical resonator. The device has a magnetic-field sensitivity of 28 pT/… ▽ More We present a highly sensitive miniaturized cavity-enhanced room-temperature magnetic-field sensor based on nitrogen-vacancy (NV) centers in diamond. The magnetic resonance signal is detected by probing absorption on the 1042\,nm spin-singlet transition. To improve the absorptive signal the diamond is placed in an optical resonator. The device has a magnetic-field sensitivity of 28 pT/$\sqrt{\rm{Hz}}$, a projected photon shot-noise-limited sensitivity of 22 pT/$\sqrt{\rm{Hz}}$ and an estimated quantum projection-noise-limited sensitivity of 0.43 pT/$\sqrt{\rm{Hz}}$ with the sensing volume of $\sim$ 390 $μ$m $\times$ 4500 $μ$m$^{2}$. The presented miniaturized device is the basis for an endoscopic magnetic field sensor for biomedical applications. △ Less

Submitted 7 June, 2017; originally announced June 2017.

Journal ref: Phys. Rev. Applied 8, 044019 (2017)

Bose-Einstein condensates in the presence of Weyl spin-orbit coupling

Authors: Ting Wu, Renyuan Liao

Abstract: We consider two-component Bose-Einstein condensates subject to Weyl spin-orbit coupling. We obtain mean-field ground state phase diagram by variational method. In the regime where interspecies coupling is larger than intraspecies coupling, the system is found to be fully polarized and condensed at a finite momentum lying along the quantization axis. We characterize this phase by studying the excit… ▽ More We consider two-component Bose-Einstein condensates subject to Weyl spin-orbit coupling. We obtain mean-field ground state phase diagram by variational method. In the regime where interspecies coupling is larger than intraspecies coupling, the system is found to be fully polarized and condensed at a finite momentum lying along the quantization axis. We characterize this phase by studying the excitation spectrum, the sound velocity, the quantum depletion of condensates, the shift of ground state energy, and the static structure factor. We find that spin-orbit coupling and interspecies coupling generally leads to competing effects. △ Less

Submitted 13 January, 2017; originally announced January 2017.

Journal ref: New J. Phys. 19 (2017)013008