Showing 1–26 of 26 results for author: Yan, S

Optical linewidth narrowing for device-coupled single T centers

Authors: Adam Johnston, Yu-En Wong, Shengbin Yan, Ulises Felix-Rendon, Songtao Chen

Abstract: Single T centers in silicon have emerged as promising optically active spins for quantum networking applications. One of the major obstacles to advancing the system is their broad optical linewidth due to spectral diffusion, which is two orders of magnitude larger than their cavity-enhanced radiative linewidth. We tackle this issue by utilizing above-band optical excitation delivered via a laser s… ▽ More Single T centers in silicon have emerged as promising optically active spins for quantum networking applications. One of the major obstacles to advancing the system is their broad optical linewidth due to spectral diffusion, which is two orders of magnitude larger than their cavity-enhanced radiative linewidth. We tackle this issue by utilizing above-band optical excitation delivered via a laser scanning microscope to device-coupled single T centers, achieving up to 70% optical linewidth reduction. We attribute the linewidth narrowing effect to the filling of nearby charge traps by photo-generated free carriers. We analyze charge stabilization dynamics by exploiting pulsed above-band excitation and develop a rate equation model to describe the dynamics and to explain the observed linewidth narrowing and center shift. This work provides an effective pathway to control and reduce the optical linewidth for single T centers, clearing one of the major roadblocks to advance the single T center spin platform for quantum information and networking applications. △ Less

Submitted 30 July, 2026; originally announced July 2026.

High-rate continuous-variable quantum key distribution coexisting with Tb/s coherent classical transmission in hollow-core fiber

Authors: Xitao Ji, Siyu Chen, Peng Li, Mingming Zhang, Yilun Chen, Jun Gao, Rui Lin, Bacco Davide, Siqi Yan, Ming Tang

Abstract: Quantum key distribution (QKD) can provide secret keys with security rooted in quantum mechanics, but operation alongside high-capacity classical traffic remains limited by the excess-noise budget of weak quantum states in conventional solid-core fiber. Here, we combine ultralow-loss anti-resonant hollow-core fiber with residual-carrier-assisted discrete-modulation continuous-variable QKD (DM-CV-Q… ▽ More Quantum key distribution (QKD) can provide secret keys with security rooted in quantum mechanics, but operation alongside high-capacity classical traffic remains limited by the excess-noise budget of weak quantum states in conventional solid-core fiber. Here, we combine ultralow-loss anti-resonant hollow-core fiber with residual-carrier-assisted discrete-modulation continuous-variable QKD (DM-CV-QKD) to address both propagation-induced coexistence noise and low-SNR phase recovery. Over a 24.3-km hollow-core link with 3.3-dB end-to-end loss, a dual-polarization 15-Gbaud DM-CV-QKD channel achieves an average asymptotic secret-key rate (SKR) of 153.22 Mb/s and a finite-size SKR of 149.99 Mb/s, while 39 coherent wavelength-division-multiplexed channels deliver an aggregate data rate of 7.6 Tb/s and a net data rate of 7.2 Tb/s. The system can even sustain a positive SKR under a high classical launch power of up to 15 dBm, without an optical bandpass filter (BPF). Finite-size analysis against collective attacks further yields a projected positive secret-key rate at a 100-km-equivalent condition. These results show that an anti-resonant hollow-core fiber, combined with carrier-assisted phase recovery, can greatly extend the operating regime of shared-fiber quantum-secured coherent links, pointing to a promising approach for integrating high-rate CV-QKD with high-capacity optical networks. △ Less

Submitted 16 July, 2026; originally announced July 2026.

Engineering Molecular Rectification: Mechanisms, Modulation Strategies, and Device Integration

Authors: Junnan Guo, Shufan Song, Wenhui Fang, Jifeng Tang, Wenhao Li, Weikang Wu, Hui Li, Shishen Yan, Lishu Zhang

Abstract: Molecular rectifiers, as prototypical components of molecular electronics, present unique opportunities for pushing device miniaturization to its ultimate limits. Nevertheless, challenges including limited rectification ratios (RR), insufficient robustness, and poor reproducibility impede their practical deployment. To make molecular rectifiers competitive with silicon-based devices, it is importa… ▽ More Molecular rectifiers, as prototypical components of molecular electronics, present unique opportunities for pushing device miniaturization to its ultimate limits. Nevertheless, challenges including limited rectification ratios (RR), insufficient robustness, and poor reproducibility impede their practical deployment. To make molecular rectifiers competitive with silicon-based devices, it is important to fully understand the design principles and fabrication methods from both mechanistic and experimental perspectives. By holistically considering the transport mechanisms, modulation strategies, fabrication, characterization techniques, and theoretical simulations, this review provides a comprehensive overview of molecular rectifiers. Representative examples of conceptually significant and high-performance molecular rectifier systems are highlighted to illustrate the relationships between rectification mechanisms, molecular design strategies, and device realization. Building on these discussions, we present an outlook for current bottlenecks and future directions to guide the development of molecular rectifiers. This review aims to serve as both a conceptual framework and a technical reference for researchers working at the intersection of molecular electronics and nanoscale device engineering in the post-CMOS era. △ Less

Submitted 27 May, 2026; originally announced May 2026.

Non-linear Sigma Model for the Surface Code with Coherent Errors

Authors: Stephen W. Yan, Yimu Bao, Sagar Vijay

Abstract: The surface code is a promising platform for a quantum memory, but its threshold under coherent errors remains incompletely understood. We study maximum-likelihood decoding of the square-lattice surface code in the presence of single-qubit unitary rotations that create electric anyon excitations. We microscopically derive a non-linear sigma model with target space $\mathrm{SO}(2n)/\mathrm{U}(n)$ a… ▽ More The surface code is a promising platform for a quantum memory, but its threshold under coherent errors remains incompletely understood. We study maximum-likelihood decoding of the square-lattice surface code in the presence of single-qubit unitary rotations that create electric anyon excitations. We microscopically derive a non-linear sigma model with target space $\mathrm{SO}(2n)/\mathrm{U}(n)$ as the effective long-distance theory of this decoding problem, with distinct replica limits: $n\to1$ for optimal decoding, which assumes knowledge of the coherent rotation angle, and $n\to0$ for suboptimal decoding with imperfect angle information. This exposes a sharp distinction between the two decoders. The suboptimal decoder supports a "thermal-metal" phase, a non-decodable regime that is qualitatively distinct from the conventional non-decodable phase of the surface code under incoherent Pauli errors. By contrast, the metal phase cannot arise in optimal decoding, since the metallic fixed-point becomes unstable in the $n\to 1$ replica limit. We argue that optimal decoding may be possible up to the maximally-coherent rotation angle. Within the sigma model description, we show that the decoding fidelity is related to twist defects of the order-parameter field, yielding quantitative predictions for its system-size dependence near the metallic fixed point for both decoders. We examine our analytic predictions for the decoding fidelity as well as other physical observables with extensive numerical simulations. We discuss how the symmetries and the target space for the sigma model rely on the lattice of the surface code, and how a stable thermal metal phase can arise in optimal decoding when the syndromes reside on a non-bipartite lattice. △ Less

Submitted 2 May, 2026; v1 submitted 26 March, 2026; originally announced March 2026.

Comments: 26+23 pages, 18 figures; typos corrected, improved figures in section VI, results unchanged

Area-Law Entanglement in Quantum Chaotic System

Authors: Chunyin Chen, Sizhe Yan, Biao Wu

Abstract: Entanglement entropy is a fundamental diagnostic for quantum chaos, typically exhibiting volume-law scaling in highly excited eigenstates of chaotic many-body systems. In this work, we present a striking counterexample: a Floquet-driven quantum many-body system with Rydberg-like blockade that, despite being fully chaotic as indicated by its Wigner-Dyson level statistics and local thermalization, e… ▽ More Entanglement entropy is a fundamental diagnostic for quantum chaos, typically exhibiting volume-law scaling in highly excited eigenstates of chaotic many-body systems. In this work, we present a striking counterexample: a Floquet-driven quantum many-body system with Rydberg-like blockade that, despite being fully chaotic as indicated by its Wigner-Dyson level statistics and local thermalization, exhibits a strict area-law entanglement entropy. Specifically, the entanglement entropy of every Floquet eigenstate is bounded by $\ln2$, independent of system size. We trace this anomaly to the specific Hilbert space structure imposed by the blockades, which restricts the Schmidt rank across a bipartition. Furthermore, we generalize this discovery by establishing a duality between constrained many-body Hamiltonians and single-particle quantum walks on median graphs, and we outline a general procedure for constructing systems with an entanglement entropy bounded by a predetermined constant. Our results demonstrate that entanglement entropy alone is an insufficient diagnostic of many-body quantum chaos and highlight the profound impact of Hilbert space geometry on quantum dynamics and thermalization. △ Less

Submitted 2 November, 2025; v1 submitted 31 October, 2025; originally announced October 2025.

LLM-based Multi-Agent Copilot for Quantum Sensor

Authors: Rong Sha, Binglin Wang, Jun Yang, Xiaoxiao Ma, Chengkun Wu, Liang Yan, Chao Zhou, Jixun Liu, Guochao Wang, Shuhua Yan, Lingxiao Zhu

Abstract: Large language models (LLM) exhibit broad utility but face limitations in quantum sensor development, stemming from interdisciplinary knowledge barriers and involving complex optimization processes. Here we present QCopilot, an LLM-based multi-agent framework integrating external knowledge access, active learning, and uncertainty quantification for quantum sensor design and diagnosis. Comprising c… ▽ More Large language models (LLM) exhibit broad utility but face limitations in quantum sensor development, stemming from interdisciplinary knowledge barriers and involving complex optimization processes. Here we present QCopilot, an LLM-based multi-agent framework integrating external knowledge access, active learning, and uncertainty quantification for quantum sensor design and diagnosis. Comprising commercial LLMs with few-shot prompt engineering and vector knowledge base, QCopilot employs specialized agents to adaptively select optimization methods, automate modeling analysis, and independently perform problem diagnosis. Applying QCopilot to atom cooling experiments, we generated 10${}^{\rm{8}}$ sub-$\rmμ$K atoms without any human intervention within a few hours, representing $\sim$100$\times$ speedup over manual experimentation. Notably, by continuously accumulating prior knowledge and enabling dynamic modeling, QCopilot can autonomously identify anomalous parameters in multi-parameter experimental settings. Our work reduces barriers to large-scale quantum sensor deployment and readily extends to other quantum information systems. △ Less

Submitted 7 August, 2025; originally announced August 2025.

Comments: 13 pages,4 figures

Chern junctions in Moiré-Patterned Graphene/PbI2

Authors: Sun Yan, M. Monteverde, V. Derkach, K. Watanabe, T. Taniguchi, F. Chiodi, H. Bouchiat, A. D. Chepelianskii

Abstract: Expanding the moire material library continues to unlock novel quantum phases and emergent electronic behaviors. Here, we introduce PbI2 into the moire family and investigate the magnetotransport properties of moire superlattice in a hexagonal boron nitride/graphene/PbI2 heterostructures. In the high-field quantum Hall regime, we observe robust dissipationless transport at the charge neutrality po… ▽ More Expanding the moire material library continues to unlock novel quantum phases and emergent electronic behaviors. Here, we introduce PbI2 into the moire family and investigate the magnetotransport properties of moire superlattice in a hexagonal boron nitride/graphene/PbI2 heterostructures. In the high-field quantum Hall regime, we observe robust dissipationless transport at the charge neutrality point, indicative of incompressible states at filling factor vh = 0. Additionally, a fractional conductance plateau at 2/3 e2/h emerges, which we attribute to a Chern junction between domains with distinct Chern numbers originating from moire-modulated and conventional integer quantum Hall states. The moire Hofstadter spectrum displays an unconventional flavor sequence, likely influenced by proximity-induced spin-orbit coupling from the PbI2 layer. We also see coherent electronic interference along lines with Chern number vm = -2. These observations provide compelling evidence for the formation of moire domains that nontrivially interrupt incompressible quantum Hall states, reflecting the strong moire potential in the BN/graphene/PbI2 superlattice. We suggest that the moire Hofstadter spectrum coupled with the proximity-induced spin-orbit interaction from PbI2 gives rise to a high magnetic field topological insulator phase explaining ballistic transport at the charge neutrality point in the graphene monolayer. △ Less

Submitted 17 April, 2026; v1 submitted 6 August, 2025; originally announced August 2025.

Comments: 9 pages, 4 figures

Quantum-Secured DSP-Lite Data Transmission Architectures for AI-Driven Data Centres

Authors: Xitao Ji, Wenjie He, Junda Chen, Mingming Zhang, Yuqi Li, Ziwen Zhou, Zhuoxuan Song, Hao Wu, Siqi Yan, Kejin Wei, Zhenrong Zhang, Shuang Wang, Ming Tang

Abstract: Artificial intelligence-driven (AI-driven) data centres, which require high-performance, scalable, energy-efficient, and secure infrastructure, have led to unprecedented data traffic demands. These demands involve low latency, high bandwidth connections, low power consumption, and data confidentiality. However, conventional optical interconnect solutions, such as intensity-modulated direct detecti… ▽ More Artificial intelligence-driven (AI-driven) data centres, which require high-performance, scalable, energy-efficient, and secure infrastructure, have led to unprecedented data traffic demands. These demands involve low latency, high bandwidth connections, low power consumption, and data confidentiality. However, conventional optical interconnect solutions, such as intensity-modulated direct detection and traditional coherent systems, cannot address these requirements simultaneously. In particular, conventional encryption protocols that rely on complex algorithms are increasingly vulnerable to the rapid advancement of quantum computing. Here, we propose and demonstrate a quantum-secured digital signal processing-lite (DSP-Lite) data transmission architecture that meets all the stringent requirements for AI-driven data centre optical interconnects (AI-DCIs) scenarios. By integrating a self-homodyne coherent (SHC) system and quantum key distribution (QKD) through the multicore-fibre-based space division multiplexing (SDM) technology, our scheme enables secure, high-capacity, and energy-efficient data transmission while ensuring resilience against quantum computing threats. In our demonstration, we achieved an expandable transmission capacity of 2 Tbit per second (Tb/s) and a quantum secret key rate (SKR) of 229.2 kb/s, with a quantum bit error rate (QBER) of approximately 1.27% and with ultralow power consumption. Our work paves the way for constructing secure, scalable, and cost-efficient data transmission frameworks, thus enabling the next generation of intelligent, leak-proof optical interconnects for data centres. △ Less

Submitted 12 March, 2025; originally announced March 2025.

Dissipative Dynamical Phase Transition as a Complex Ising Model

Authors: Stephen W. Yan, Diego Barberena, Matthew P. A. Fisher, Sagar Vijay

Abstract: We investigate a quantum dynamical phase transition induced by the competition between local unitary evolution and dissipation in a qubit chain with a strong, on-site $\mathbb{Z}_2$ symmetry. While the steady-state of this evolution is always maximally-mixed, we show that the dynamical behavior of certain non-local observables on the approach to this steady-state is dictated by a quantum Ising mod… ▽ More We investigate a quantum dynamical phase transition induced by the competition between local unitary evolution and dissipation in a qubit chain with a strong, on-site $\mathbb{Z}_2$ symmetry. While the steady-state of this evolution is always maximally-mixed, we show that the dynamical behavior of certain non-local observables on the approach to this steady-state is dictated by a quantum Ising model with a $\textit{complex}$ transverse-field (cTFIM). We investigate these observables analytically, uncovering a dynamical phase transition as the relative rate of unitary evolution and dissipation is tuned. We show that the weak-dissipation limit corresponds to a cTFIM with a large magnitude of the imaginary transverse-field, for which the many-body "ground-state" (with smallest real eigenvalue) is gapless, exhibiting quasi-long-range correlations of the local magnetization with a continuously-varying exponent. Correspondingly, the dynamics of the non-local observables show oscillatory behavior with an amplitude decaying exponentially in time. The strong-dissipation limit corresponds to a gapped ferromagnetic phase of the cTFIM, and non-local observables show exponential decay on the approach to equilibrium. This transition in (1+1)-dimensions has a peculiar, "two-sided" nature appearing as either first- or second-order depending on the phase from which the transition is approached, an analytic result which is corroborated by numerical studies. In higher dimensions, we present a field-theoretic understanding of the first-order nature of this transition, when approaching from the ferromagnetic phase of the cTFIM, though the nature of the phase with large imaginary transverse-field remains to be understood. △ Less

Submitted 12 December, 2024; originally announced December 2024.

Comments: 15 + 14 pages, 8 figures

One-dimensional quantum dot array integrated with charge sensors in an InAs nanowire

Authors: Yi Luo, Xiao-Fei Liu, Zhi-Hai Liu, Weijie Li, Shili Yan, Han Gao, Haitian Su, Dong Pan, Jianhua Zhao, Ji-Yin Wang, H. Q. Xu

Abstract: We report an experimental study of a one-dimensional quintuple-quantum-dot array integrated with two quantum dot charge sensors in an InAs nanowire. The device is studied by measuring double quantum dots formed consecutively in the array and corresponding charge stability diagrams are revealed with both direct current measurements and charge sensor signals. The one-dimensional quintuple-quantum-do… ▽ More We report an experimental study of a one-dimensional quintuple-quantum-dot array integrated with two quantum dot charge sensors in an InAs nanowire. The device is studied by measuring double quantum dots formed consecutively in the array and corresponding charge stability diagrams are revealed with both direct current measurements and charge sensor signals. The one-dimensional quintuple-quantum-dot array are then tuned up and its charge configurations are fully mapped out with the two charge sensors. The energy level of each dot in the array can be controlled individually by using a compensated gate architecture (i.e., "virtual gate"). After that, four dots in the array are selected to form two double quantum dots and ultra strong inter-double-dot interaction is obtained. A theoretical simulation based on a 4-dimensional Hamiltonian confirms the strong coupling strength between the two double quantum dots. The highly controllable one-dimensional quantum dot array achieved in this work is expected to be valuable for employing InAs nanowires to construct advanced quantum hardware in the future. △ Less

Submitted 22 July, 2024; originally announced July 2024.

Spectral form factor in chaotic, localized, and integrable open quantum many-body systems

Authors: Jiachen Li, Stephen Yan, Tomaž Prosen, Amos Chan

Abstract: We numerically study the spectral statistics of open quantum many-body systems (OQMBS) as signatures of quantum chaos (or the lack thereof), using the dissipative spectral form factor (DSFF), a generalization of the spectral form factor to complex spectra. We show that the DSFF of chaotic OQMBS generically displays the $\textit{quadratic}$ ramp-plateau behaviour of the Ginibre ensemble from random… ▽ More We numerically study the spectral statistics of open quantum many-body systems (OQMBS) as signatures of quantum chaos (or the lack thereof), using the dissipative spectral form factor (DSFF), a generalization of the spectral form factor to complex spectra. We show that the DSFF of chaotic OQMBS generically displays the $\textit{quadratic}$ ramp-plateau behaviour of the Ginibre ensemble from random matrix theory, in contrast to the linear ramp-plateau behaviour of the Gaussian ensemble in closed quantum systems. Furthermore, in the presence of many-body interactions, such RMT behaviour emerges only after a time scale $τ_{\mathrm{dev}}$, which generally increases with system size for sufficiently large system size, and can be identified as the non-Hermitian analogue of the $\textit{many-body Thouless time}$. The universality of the random matrix theory behavior is demonstrated by surveying twelve models of OQMBS, including random Kraus circuits (quantum channels) and random Lindbladians (Liouvillians) in several symmetry classes, as well as Lindbladians of paradigmatic models such as the Sachdev-Ye-Kitaev (SYK), XXZ, and the transverse field Ising models. We devise an unfolding and filtering procedure to remove variations of the averaged density of states which would otherwise hide the universal RMT-like signatures in the DSFF for chaotic OQMBS. Beyond chaotic OQMBS, we study the spectral statistics of non-chaotic OQMBS, specifically the integrable XX model and a system in the many-body localized (MBL) regime in the presence of dissipation, which exhibit DSFF behaviours distinct from the ramp-plateau behaviour of random matrix theory. Lastly, we study the DSFF of Lindbladians with the Hamiltonian term set to zero, i.e. only the jump operators are present, and demonstrate that the results of RMT universality and scaling of many-body Thouless time survive even without coherent evolution. △ Less

Submitted 2 May, 2024; originally announced May 2024.

Evaluation of the systematic error induced by quadratic Zeeman effect using hyperfine ground state exchange method in a long-baseline dual-species atom interferometer

Authors: Yu-Hang Ji, Chuan He, Si-Tong Yan, Jun-Jie Jiang, Jia-Qi Lei, Lu Zhou, Lin Zhou, Xi Chen, Jin Wang, Ming-Sheng Zhan

Abstract: The systematic error induced by the quadratic Zeeman effect is non-negligible in atom interferometers and must be precisely evaluated. We theoretically analyze the phase shift induced by the Zeeman effect, and use a hyperfine ground state exchange (HGSE) method to evaluate the systematic error in the long-baseline $^{85}$Rb-$^{87}$Rb dual-species atom interferometer due to the quadratic Zeeman eff… ▽ More The systematic error induced by the quadratic Zeeman effect is non-negligible in atom interferometers and must be precisely evaluated. We theoretically analyze the phase shift induced by the Zeeman effect, and use a hyperfine ground state exchange (HGSE) method to evaluate the systematic error in the long-baseline $^{85}$Rb-$^{87}$Rb dual-species atom interferometer due to the quadratic Zeeman effect. Compared to the two evaluation methods, mapping the absolute magnetic field in the interference region and performing phase measurements at different bias fields, the HGSE method could obtain the systematic error in real time in case of slow drifts of either the ambient magnetic field or other systematic effects irrelevant to the hyperfine ground states. To validate the effectiveness of the HGSE method, we also employ the mapping magnetic field method and modulating bias field method independently to cross-check and yield consistent results of three methods within an accuracy of $10^{-11}$ level. The HGSE method is helpful in evaluating and suppressing the quadratic Zeeman-effect-induced systematic error in long-baseline atom interferometer-based precision measurements, such as equivalence principle tests. △ Less

Submitted 1 April, 2024; originally announced April 2024.

Two-level approximation of transmons in quantum quench experiments

Authors: H. S. Yan, Yong-Yi Wang, S. K. Zhao, Z. H. Yang, Z. T. Wang, Kai Xu, Ye Tian, H. F. Yu, Heng Fan, S. P. Zhao

Abstract: Quantum quench is a typical protocol in the study of nonequilibrium dynamics of quantum many-body systems. Recently, a number of experiments with superconducting transmon qubits are reported, in which the spin and hard-core boson models with two energy levels on individual sites are used. The transmons are a multilevel system and the coupled qubits are governed by the Bose-Hubbard model. How well… ▽ More Quantum quench is a typical protocol in the study of nonequilibrium dynamics of quantum many-body systems. Recently, a number of experiments with superconducting transmon qubits are reported, in which the spin and hard-core boson models with two energy levels on individual sites are used. The transmons are a multilevel system and the coupled qubits are governed by the Bose-Hubbard model. How well they can be approximated by a two-level system has been discussed and analysed in different ways for specific experiments in the literature. Here, we numerically investigate the accuracy and validity of the two-level approximation for the multilevel transmons based on the concept of Loschmidt echo. Using this method, we are able to calculate the fidelity decay (i.e., the time-dependent overlap of evolving wave functions) due to the state leakage to transmon high energy levels. We present the results for different system Hamiltonians with various initial states, qubit coupling strength, and external driving, and for two kinds of quantum quench experiments with time reversal and time evolution in one direction. We show quantitatively the extent to which the fidelity decays with time for changing coupling strength (or on-site interaction over coupling strength) and filled particle number or locations in the initial states under specific system Hamiltonians, which may serve as a way for assessing the two-level approximation of transmons. Finally, we compare our results with the reported experiments using transmon qubits. △ Less

Submitted 4 October, 2023; v1 submitted 10 February, 2023; originally announced February 2023.

A Characterization of Perfect Strategies for Mirror Games

Authors: Sizhuo Yan, Jianting Yang, Tianshi Yu, Lihong Zhi

Abstract: We associate mirror games with the universal game algebra and use the *-representation to describe quantum commuting operator strategies. We provide an algebraic characterization of whether or not a mirror game has perfect commuting operator strategies. This new characterization uses a smaller algebra introduced by Paulsen and others for synchronous games and the noncommutative Nullstellensatz dev… ▽ More We associate mirror games with the universal game algebra and use the *-representation to describe quantum commuting operator strategies. We provide an algebraic characterization of whether or not a mirror game has perfect commuting operator strategies. This new characterization uses a smaller algebra introduced by Paulsen and others for synchronous games and the noncommutative Nullstellensatz developed by Cimpric, Helton and collaborators. An algorithm based on noncommutative Gröbner basis computation and semidefinite programming is given for certifying that a given mirror game has no perfect commuting operator strategies. △ Less

Submitted 11 May, 2023; v1 submitted 9 February, 2023; originally announced February 2023.

Comments: To appear ISSAC'2023 Proc. 2023 Internat. Symp. Symbolic Algebraic Comput

$O(N^2)$ Universal Antisymmetry in Fermionic Neural Networks

Authors: Tianyu Pang, Shuicheng Yan, Min Lin

Abstract: Fermionic neural network (FermiNet) is a recently proposed wavefunction Ansatz, which is used in variational Monte Carlo (VMC) methods to solve the many-electron Schrödinger equation. FermiNet proposes permutation-equivariant architectures, on which a Slater determinant is applied to induce antisymmetry. FermiNet is proved to have universal approximation capability with a single determinant, namel… ▽ More Fermionic neural network (FermiNet) is a recently proposed wavefunction Ansatz, which is used in variational Monte Carlo (VMC) methods to solve the many-electron Schrödinger equation. FermiNet proposes permutation-equivariant architectures, on which a Slater determinant is applied to induce antisymmetry. FermiNet is proved to have universal approximation capability with a single determinant, namely, it suffices to represent any antisymmetric function given sufficient parameters. However, the asymptotic computational bottleneck comes from the Slater determinant, which scales with $O(N^3)$ for $N$ electrons. In this paper, we substitute the Slater determinant with a pairwise antisymmetry construction, which is easy to implement and can reduce the computational cost to $O(N^2)$. We formally prove that the pairwise construction built upon permutation-equivariant architectures can universally represent any antisymmetric function. Besides, this universality can be achieved via continuous approximators when we aim to represent ground-state wavefunctions. △ Less

Submitted 16 June, 2022; v1 submitted 26 May, 2022; originally announced May 2022.

Comments: ICML 2022 AI for Science Workshop

Probing Operator Spreading via Floquet Engineering in a Superconducting Circuit

Authors: S. K. Zhao, Zi-Yong Ge, Zhongcheng Xiang, G. M. Xue, H. S. Yan, Z. T. Wang, Zhan Wang, H. K. Xu, F. F. Su, Z. H. Yang, He Zhang, Yu-Ran Zhang, Xue-Yi Guo, Kai Xu, Ye Tian, H. F. Yu, D. N. Zheng, Heng Fan, S. P. Zhao

Abstract: Operator spreading, often characterized by out-of-time-order correlators (OTOCs), is one of the central concepts in quantum many-body physics. However, measuring OTOCs is experimentally challenging due to the requirement of reversing the time evolution of systems. Here we apply Floquet engineering to investigate operator spreading in a superconducting 10-qubit chain. Floquet engineering provides a… ▽ More Operator spreading, often characterized by out-of-time-order correlators (OTOCs), is one of the central concepts in quantum many-body physics. However, measuring OTOCs is experimentally challenging due to the requirement of reversing the time evolution of systems. Here we apply Floquet engineering to investigate operator spreading in a superconducting 10-qubit chain. Floquet engineering provides an effective way to tune the coupling strength between nearby qubits, which is used to demonstrate quantum walks with tunable couplings, reversed time evolution, and the measurement of OTOCs. A clear light-cone-like operator propagation is observed in the system with multiple excitations, and has a nearly equal velocity as the single-particle quantum walk. For the butterfly operator that is nonlocal (local) under the Jordan-Wigner transformation, the OTOCs show distinct behaviors with (without) a signature of information scrambling in the near integrable system. △ Less

Submitted 10 August, 2022; v1 submitted 2 August, 2021; originally announced August 2021.

Comments: 6+12 pages, 4 figures

Journal ref: Phys. Rev. Lett.129, 160602 (2022)

An unsupervised feature learning for quantum-classical convolutional network with applications to fault detection

Authors: Tong Dou, Zhenwei Zhou, Kaiwei Wang, Shilu Yan, Wei Cui

Abstract: Combining the advantages of quantum computing and neural networks, quantum neural networks (QNNs) have gained considerable attention recently. However, because of the lack of quantum resource, it is costly to train QNNs. In this work, we presented a simple unsupervised method for quantum-classical convolutional networks to learn a hierarchy of quantum feature extractors. Each level of the resultin… ▽ More Combining the advantages of quantum computing and neural networks, quantum neural networks (QNNs) have gained considerable attention recently. However, because of the lack of quantum resource, it is costly to train QNNs. In this work, we presented a simple unsupervised method for quantum-classical convolutional networks to learn a hierarchy of quantum feature extractors. Each level of the resulting feature extractors consist of multiple quanvolution filters, followed by a pooling layer. The main contribution of the proposed approach is to use the $K$-means clustering to maximize the difference of quantum properties in quantum circuit ansatz. One experiment on the bearing fault detection task shows the effectiveness of the proposed method. △ Less

Submitted 16 July, 2021; originally announced July 2021.

Module for arbitrary controlled rotation in gate-based quantum algorithms

Authors: Shilu Yan, Tong Dou, Runqiu Shu, Wei Cui

Abstract: To assess whether a gate-based quantum algorithm can be executed successfully on a noisy intermediate-scale quantum (NISQ) device, both complexity and actual value of quantum resources should be considered carefully. Based on quantum phase estimation, we implemente arbitrary controlled rotation of quantum algorithms with a proposed modular method. The proposed method is not limited to be used as a… ▽ More To assess whether a gate-based quantum algorithm can be executed successfully on a noisy intermediate-scale quantum (NISQ) device, both complexity and actual value of quantum resources should be considered carefully. Based on quantum phase estimation, we implemente arbitrary controlled rotation of quantum algorithms with a proposed modular method. The proposed method is not limited to be used as a submodule of the HHL algorithm and can be applied to more general quantum machine learning algorithms. Compared with the polynomial-fitting function method, our method only requires the least ancillas and the least quantum gates to maintain the high fidelity of quantum algorithms. The method theoretically will not influence the acceleration of original algorithms. Numerical simulations illustrate the effectiveness of the proposed method. Furthermore, if the corresponding diagonal unitary matrix can be effectively decomposed, the method is also polynomial in time cost. △ Less

Submitted 16 July, 2021; originally announced July 2021.

Nonlinear Quantum Neuron: A Fundamental Building Block for Quantum Neural Networks

Authors: Shilu Yan, Hongsheng Qi, Wei Cui

Abstract: Quantum computing enables quantum neural networks (QNNs) to have great potentials to surpass artificial neural networks (ANNs). The powerful generalization of neural networks is attributed to nonlinear activation functions. Although various models related to QNNs have been developed, they are facing the challenge of merging the nonlinear, dissipative dynamics of neural computing into the linear, u… ▽ More Quantum computing enables quantum neural networks (QNNs) to have great potentials to surpass artificial neural networks (ANNs). The powerful generalization of neural networks is attributed to nonlinear activation functions. Although various models related to QNNs have been developed, they are facing the challenge of merging the nonlinear, dissipative dynamics of neural computing into the linear, unitary quantum system. In this paper, we establish different quantum circuits to approximate nonlinear functions and then propose a generalizable framework to realize any nonlinear quantum neuron. We present two quantum neuron examples based on the proposed framework. The quantum resources required to construct a single quantum neuron are the polynomial, in function of the input size. Finally, both IBM Quantum Experience results and numerical simulations illustrate the effectiveness of the proposed framework. △ Less

Submitted 6 November, 2020; originally announced November 2020.

Comments: 9 pages, 8 figures

Journal ref: Phys. Rev. A 102, 052421 (2020)

United test of the equivalence principle at $10^{-10}$ level using mass and internal energy specified atoms

Authors: Lin Zhou, Chuan He, Si-Tong Yan, Xi Chen, Wei-Tao Duan, Run-Dong Xu, Chao Zhou, Yu-Hang Ji, Sachin Barthwal, Qi Wang, Zhuo Hou, Zong-Yuan Xiong, Dong-Feng Gao, Yuan-Zhong Zhang, Wei-Tou Ni, Jin Wang, Ming-Sheng Zhan

Abstract: We use both mass and internal energy specified rubidium atoms to jointly test the weak equivalence principle (WEP). We improve the four-wave double-diffraction Raman transition method (FWDR) we proposed before to select atoms with certain mass and angular momentum state, and perform dual-species atom interferometer. By combining $^{87}$Rb and $^{85}$Rb atoms with different angular momenta, we comp… ▽ More We use both mass and internal energy specified rubidium atoms to jointly test the weak equivalence principle (WEP). We improve the four-wave double-diffraction Raman transition method (FWDR) we proposed before to select atoms with certain mass and angular momentum state, and perform dual-species atom interferometer. By combining $^{87}$Rb and $^{85}$Rb atoms with different angular momenta, we compare the differential gravitational acceleration of them, and determine the value of Eötvös parameter, $η$, which measures the strength of the violation of WEP. For one case ($^{87}$Rb$|\emph{F}=1\rangle$ - $^{85}$Rb$|\emph{F}=2\rangle$),the statistical uncertainty of $η$ is $1.8 \times 10^{-10}$ at integration time of 8960 s. With various systematic errors correction, the final value is $η=(-4.4 \pm 6.7) \times 10^{-10}$. Comparing with the previous WEP test experiments using atoms, this work gives a new upper limit of WEP violation for $^{87}$Rb and $^{85}$Rb atom pairs. △ Less

Submitted 23 April, 2019; v1 submitted 15 April, 2019; originally announced April 2019.

Comments: 5 pages, 3 figures

Journal ref: Phys. Rev. A 104, 022822 (2021)

Field-Trial of Machine Learning-Assisted Quantum Key Distribution (QKD) Networking with SDN

Authors: Y. Ou, E. Hugues-Salas, F. Ntavou, R. Wang, Y. Bi, SY. Yan, G. Kanellos, R. Nejabati, D. Simeonidou

Abstract: We demonstrated, for the first time, a machine-learning method to assist the coexistence between quantum and classical communication channels. Software-defined networking was used to successfully enable the key generation and transmission over a city and campus network. We demonstrated, for the first time, a machine-learning method to assist the coexistence between quantum and classical communication channels. Software-defined networking was used to successfully enable the key generation and transmission over a city and campus network. △ Less

Submitted 18 July, 2018; originally announced July 2018.

Scheme for suppressing atom expansion induced contrast loss in atom interferometers

Authors: Qing-Qing Hu, Yu-Kun Luo, Ai-Ai Jia, Chun-Hua Wei, Shu-Hua Yan, Jun Yang

Abstract: The loss of contrast due to atom expansion induced non-perfect Raman pulse area in atom interferometers is investigated systematically. Based on the theoretical simulation, we find that the expansion of the atomic cloud results in a decrease of the π pulse fidelity and a change of the π pulse duration, which lead to a significant reduction in fringe contrast. We propose a mitigation strategy of in… ▽ More The loss of contrast due to atom expansion induced non-perfect Raman pulse area in atom interferometers is investigated systematically. Based on the theoretical simulation, we find that the expansion of the atomic cloud results in a decrease of the π pulse fidelity and a change of the π pulse duration, which lead to a significant reduction in fringe contrast. We propose a mitigation strategy of increasing the intensities of the second and third Raman pulses. Simulation results show that the fringe contrast can be improved by 13.6% in a typical atom interferometer gravimeter using this intensity compensation strategy. We also evaluate the effects of this mitigation strategy in the case of a lower atomic cloud temperature and a larger Raman beam size under different Raman pulse time interval conditions. This mitigation strategy has potential applications in increasing the sensitivity of atom interferometer-based precision measuring, including precision measuring of the gravity, gravity gradient, rotation, and magnetic field gradient, as well as testing of the Einstein equivalence principle. △ Less

Submitted 15 May, 2018; originally announced May 2018.

Comments: 14 pages, 8 figures

Journal ref: Optics Communications 2016

Quantum noise effects with Kerr nonlinearity enhancement in coupled gain-loss waveguides

Authors: Bing He, Shu-Bin Yan, Jing Wang, Min Xiao

Abstract: It is generally difficult to study the dynamical properties of a quantum system with both inherent quantum noises and non-perturbative nonlinearity. Due to the possibly drastic intensity increase of an input coherent light in the gain-loss waveguide couplers with parity-time (PT) symmetry, the Kerr effect from a nonlinearity added into the systems can be greatly enhanced, and is expected to create… ▽ More It is generally difficult to study the dynamical properties of a quantum system with both inherent quantum noises and non-perturbative nonlinearity. Due to the possibly drastic intensity increase of an input coherent light in the gain-loss waveguide couplers with parity-time (PT) symmetry, the Kerr effect from a nonlinearity added into the systems can be greatly enhanced, and is expected to create the macroscopic entangled states of the output light fields with huge photon numbers. Meanwhile, the quantum noises also coexist with the amplification and dissipation of the light fields. Under the interplay between the quantum noises and nonlinearity, the quantum dynamical behaviors of the systems become rather complicated. However, the important quantum noise effects have been mostly neglected in the previous studies about nonlinear PT-symmetric systems. Here we present a solution to this non-perturbative quantum nonlinear problem, showing the real-time evolution of the system observables. The enhanced Kerr nonlinearity is found to give rise to a previously unknown decoherence effect that is irrelevant to the quantum noises, and imposes a limit on the emergence of macroscopic nonclassicality. In contrast to what happen in the linear systems, the quantum noises exert significant impact on the system dynamics, and can create the nonclassical light field states in conjunction with the enhanced Kerr nonlinearity. This first study on the noise involved quantum nonlinear dynamics of the coupled gain-loss waveguides can help to better understand the quantum noise effects in the broad nonlinear systems. △ Less

Submitted 25 May, 2015; v1 submitted 3 August, 2014; originally announced August 2014.

Comments: 15 pages, 7 figures

Journal ref: Phys. Rev. A 91, 053832 (2015)

Theoretical comparison of quantum and thermal noise squeezing in silicon and graphene nanoresonators

Authors: Sheping Yan, Yang Xu, Zhonghe Jin, Yuelin Wang

Abstract: We theoretically compared quantum noise squeezing differences between silicon and graphene nanoresonators based on experimental structure parameters. The conditions to achieve squeezed states of silicon and graphene have been discussed. According to our theoretical analysis, graphene nanoresonators can obtain a much smaller squeezing factor than silicon, taking advantage of their thin thickness. B… ▽ More We theoretically compared quantum noise squeezing differences between silicon and graphene nanoresonators based on experimental structure parameters. The conditions to achieve squeezed states of silicon and graphene have been discussed. According to our theoretical analysis, graphene nanoresonators can obtain a much smaller squeezing factor than silicon, taking advantage of their thin thickness. Both the quantum noise and thermal noise (Brownian motion) of typical monolayer graphene nanoresonator can be reduced by 12.58 dB at T = 5 K with a pump voltage of 5 V. △ Less

Submitted 28 January, 2011; originally announced January 2011.

Comments: 4pages,5figures

Spin Liquid Ground State of the $S=1/2$ Kagome Heisenberg Model

Authors: Simeng Yan, David A. Huse, Steven R. White

Abstract: Condensed matter physicists have long sought a realistic two-dimensional (2D) magnetic system whose ground state is a {\it spin liquid}---a zero temperature state in which quantum fluctuations have melted away any form of magnetic order. The nearest-neighbor $S=1/2$ Heisenberg model on the kagome lattice has seemed an ideal candidate, but in recent years some approximate numerical approaches to it… ▽ More Condensed matter physicists have long sought a realistic two-dimensional (2D) magnetic system whose ground state is a {\it spin liquid}---a zero temperature state in which quantum fluctuations have melted away any form of magnetic order. The nearest-neighbor $S=1/2$ Heisenberg model on the kagome lattice has seemed an ideal candidate, but in recent years some approximate numerical approaches to it have yielded instead a valence bond crystal. We have used the density matrix renormalization group to perform very accurate simulations on numerous cylinders with circumferences up to 12 lattice spacings, finding instead of the valence bond crystal a singlet-gapped spin liquid with substantially lower energy that appears to have $Z_2$ topological order. Our results, through a combination of very low energy, short correlation lengths and corresponding small finite size effects, a new rigorous energy bound, and consistent behavior on many cylinders, provide strong evidence that the 2D ground state of this model is a gapped spin liquid. △ Less

Submitted 28 November, 2010; originally announced November 2010.

Comments: 8 pages, 7 figures

Journal ref: Science 332, 1173-1176 (2011)

Observation of sub-Doppler absorption in the /Lambda-type three-level Doppler-broadened cesium system

Authors: Junmin Wang, Yanhua Wang, Shubin Yan, Tao Liu, Tiancai Zhang

Abstract: Thanks to the atomic coherence in coupling laser driven atomic system, sub-Doppler absorption has been observed in Doppler-broadened cesium vapor cell via the /Lambda-type three-level scheme. The linewidth of the sub-Doppler absorption peak become narrower while the frequency detuning of coupling laser increases. The results are in agreement with the theoretical prediction by G. Vemuri et al.[PR… ▽ More Thanks to the atomic coherence in coupling laser driven atomic system, sub-Doppler absorption has been observed in Doppler-broadened cesium vapor cell via the /Lambda-type three-level scheme. The linewidth of the sub-Doppler absorption peak become narrower while the frequency detuning of coupling laser increases. The results are in agreement with the theoretical prediction by G. Vemuri et al.[PRA,Vol.53(1996) p.2842]. △ Less

Submitted 30 December, 2003; originally announced December 2003.

Comments: 12 pages, 5 figures, to appear on Applied Physics B