Showing 1–50 of 293 results for author: Zhou, X

Super-Moiré Spin Textures in Twisted Antiferromagnets

Authors: King Cho Wong, Ruoming Peng, Eric Anderson, Jackson Ross, Bowen Yang, Meixin Cheng, Sreehari Jayaram, Malik Lenger, Xuankai Zhou, Yan Tung Kong, Takashi Taniguchi, Kenji Watanabe, Michael A. McGuire, Rainer Stöhr, Adam Wei Tsen, Elton J. G. Santos, Xiaodong Xu, Jörg Wrachtrup

Abstract: Stacking two-dimensional (2D) layered materials offers a powerful platform to engineer electronic and magnetic states. In general, the resulting states, such as Moiré magnetism, have a periodicity at the length scale of the Moiré unit cell. Here, we report a new type of magnetism -- dubbed a super-Moiré magnetic state -- which is characterized by long-range magnetic textures extending beyond the s… ▽ More Stacking two-dimensional (2D) layered materials offers a powerful platform to engineer electronic and magnetic states. In general, the resulting states, such as Moiré magnetism, have a periodicity at the length scale of the Moiré unit cell. Here, we report a new type of magnetism -- dubbed a super-Moiré magnetic state -- which is characterized by long-range magnetic textures extending beyond the single Moiré unit cell -- in twisted double bilayer chromium triiodide (tDB CrI$_3$). We found that at small twist angles, the size of the spontaneous magnetic texture increases with twist angle, opposite to the underlying Moiré periodicity. The spin-texture size reaches a maximum of about 300 nm in 1.1$°$ twisted devices, an order of magnitude larger than the underlying Moiré wavelength, and vanishes at twist angles above 2$°$. Employing scanning quantum spin magnetometry, the obtained vector field maps suggest the formation of antiferromagnetic Néel-type skyrmions spanning multiple Moiré cells. The twist-angle-dependent study combined with large-scale atomistic simulations suggests that complex magnetic competition between the Dzyaloshinskii--Moriya interaction, magnetic anisotropy, and exchange interactions controlled by the relative rotation of the layers produces the topological textures which arise in the super-Moiré spin orders. △ Less

Submitted 29 October, 2025; originally announced October 2025.

Characterizing and Harnessing Correlations Featuring Independent Qubit Devices

Authors: Liang-Liang Sun, Xiang Zhou, Chengjie Zhang, Zizhu Wang, Yong-Shun Song, Sixia Yu

Abstract: We propose a framework to characterize the correlations in qubit systems for Bell and prepare-and-measure scenarios with independent devices -- a typically non-convex problem. Based on this result, we introduce protocols for referring devices and detecting entanglement with correlation that are not necessarily extreme or nonlocal, as required by common linear approach. } Specifically, our correlat… ▽ More We propose a framework to characterize the correlations in qubit systems for Bell and prepare-and-measure scenarios with independent devices -- a typically non-convex problem. Based on this result, we introduce protocols for referring devices and detecting entanglement with correlation that are not necessarily extreme or nonlocal, as required by common linear approach. } Specifically, our correlation criterion, derived from uncertainty relation specific to qubit systems, can capture the non-convex nature of the set of correlations arising from Bell and prepare-and-measure scenarios, as demonstrated through concrete examples. Conversely, when given an observed correlation, our framework can refer potential measurements and quantum states -- which are sometimes uniquely determined -- even with correlations that are not extreme. This extends common protocols that merely verify devices using extreme correlations. We then enhance entanglement detection for qubit system by incorporating the inferred information in Navascués-Pironio-Acín (NPA) hierarchy, showing that some local correlations can also verify entanglement. Since the scenarios considered here are standard platforms for most quantum information protocols and device inference is a central issue in quantum information science, our methodology, which is well-suited to these tasks, may provide a foundation for a broad range of applications. △ Less

Submitted 13 October, 2025; originally announced October 2025.

Experimental demonstration of genuine quantum information transmission through completely depolarizing channels in a superposition of cyclic orders

Authors: Yaxin Wang, Linxiang Zhou, Tianfeng Feng, Hanlin Nie, Ying Xia, Tianqi Xiao, Juntao Li, Vlatko Vedral, Xiaoqi Zhou

Abstract: A major challenge in quantum communication is addressing the negative effects of noise on channel capacity, especially for completely depolarizing channels, where information transmission is inherently impossible. The concept of indefinite causal order provides a promising solution by allowing control over the sequence in which channels are applied. We experimentally demonstrate the activation of… ▽ More A major challenge in quantum communication is addressing the negative effects of noise on channel capacity, especially for completely depolarizing channels, where information transmission is inherently impossible. The concept of indefinite causal order provides a promising solution by allowing control over the sequence in which channels are applied. We experimentally demonstrate the activation of quantum communication through completely depolarizing channels using a programmable silicon photonic quantum chip. By implementing configurations based on the superposition of cyclic orders, a form of indefinite causal order, we report the first experimental realization of genuine quantum information transmission across multiple concatenated completely depolarizing channels. Our results show that when four completely depolarizing channels are combined using the superposition of cyclic orders, the fidelity of the output state is $0.712 \pm 0.013$, significantly exceeding the classical threshold of 2/3. Our work establishes indefinite causal order as a powerful tool for overcoming noise-induced limitations in quantum communication, demonstrating its potential in high-noise environments and opening new possibilities for building robust quantum networks. △ Less

Submitted 8 October, 2025; originally announced October 2025.

Comments: 6 pages, 3 figues

Scalable Network of Mach-Zehnder Interferometers with a Single Entangled Resource

Authors: Zhihui Yan, Yanni Feng, Luca Pezze, Zhaoqing Zeng, Jingxu Ma, Xiaoyu Zhou, Augusto Smerzi, Xiaojun Jia, Kunchi Peng

Abstract: Distributed quantum sensing exploits entanglement to enhance the estimation of multiple parameters across a network of spatially-separated sensors, achieving sensitivities beyond the classical limit. Potential applications cover a plethora of technologies, from precision navigation to biomedical imaging and environmental monitoring. However, practical implementations are challenged by the complex… ▽ More Distributed quantum sensing exploits entanglement to enhance the estimation of multiple parameters across a network of spatially-separated sensors, achieving sensitivities beyond the classical limit. Potential applications cover a plethora of technologies, from precision navigation to biomedical imaging and environmental monitoring. However, practical implementations are challenged by the complex optimal distribution of entanglement throughout the sensing nodes, which affects scalability and robustness. Here we demonstrate a reconfigurable network of Mach-Zehnder interferometers entangled via a single shared squeezed-vacuum resource. We achieve joint noise suppression of $4.36 \pm 0.35$ dB below the standard quantum limit at the phase-uncertainty level of $10^{-9}$ . Furthermore, after full optimization in the low-intensity regime, we demonstrate a crossover from the standard quantum limit to the Heisenberg limit. The network estimates arbitrary linear combinations of phases, saturates the quantum Cramer-Rao bound in the ideal case, remains robust under realistic photon losses, and scales favorably with the number of sensors. △ Less

Submitted 9 September, 2025; originally announced September 2025.

Dynamically encircling an exceptional point through phase-tracked closed-loop control

Authors: Sen Zhang, Yangyu Huang, Lei Yu, Kaixuan He, Ning Zhou, Dingbang Xiao, Xuezhong Wu, Franco Nori, Hui Jing, Xin Zhou

Abstract: The intricate complex eigenvalues of non-Hermitian Hamiltonians manifest as Riemann surfaces in control parameter spaces. At the exceptional points (EPs), the degeneracy of both eigenvalues and eigenvectors introduces noteworthy topological features, particularly during the encirclement of the EPs. Traditional methods for probing the state information on the Riemann surfaces involve static measure… ▽ More The intricate complex eigenvalues of non-Hermitian Hamiltonians manifest as Riemann surfaces in control parameter spaces. At the exceptional points (EPs), the degeneracy of both eigenvalues and eigenvectors introduces noteworthy topological features, particularly during the encirclement of the EPs. Traditional methods for probing the state information on the Riemann surfaces involve static measurements; however, realizing continuous encircling remains a formidable challenge due to non-adiabatic transitions that disrupt the transport paths. Here we propose an approach leveraging the phase-locked loop (PLL) technique to facilitate smooth, dynamic encircling of EPs while maintaining resonance. Our methodology strategically ties the excitation frequencies of steady states to their response phases, enabling controlled traversal along the Riemann surfaces of real eigenvalues. This study advances the concept of phase-tracked dynamical encircling and explores its practical implementation within a fully electrically controlled non-Hermitian microelectromechanical system, highlighting robust in-situ tunability and providing methods for exploring non-Hermitian topologies. △ Less

Submitted 5 September, 2025; originally announced September 2025.

Comments: 43 pages, 12 figures

Journal ref: Commun Phys 8, 344 (2025)

Deformation-Driven Enhancement of Spin Defect Emission in Hexagonal Boron Nitride

Authors: Jianpei Geng, Xuankai Zhou, Nils Gross, Song Li, Yan Tung Kong, Jixing Zhang, Guodong Bian, San Lam Ng, Cheng-I Ho, Andrej Denisenko, Rainer Stöhr, Ruoming Peng, Jurgen Smet, Jörg Wrachtrup

Abstract: The negatively charged boron vacancy (VB-) in hexagonal boron nitride (hBN) has been extensively investigated as it offers a novel playground for two-dimensional quantum sensing, with ultimate proximity to target samples. However, its practical sensitivity is limited by the intrinsically weak photoluminescence of the spin ensemble. Here, we report a photoluminescence enhancement of up to 30 times… ▽ More The negatively charged boron vacancy (VB-) in hexagonal boron nitride (hBN) has been extensively investigated as it offers a novel playground for two-dimensional quantum sensing, with ultimate proximity to target samples. However, its practical sensitivity is limited by the intrinsically weak photoluminescence of the spin ensemble. Here, we report a photoluminescence enhancement of up to 30 times from VB- centers in suspended regions of hBN compared to those in substrate-supported areas. The key spin properties, such as the optically detected magnetic resonance (ODMR) contrast and linewidth, as well as the spin lifetime, of the VB- centers in this region are well preserved. Detailed investigations, including measurements of zero-field ODMR, Raman spectroscopy, and Kelvin probe force microscopy, reveal a correlation between emission enhancement and local deformation in the sample. It is concluded that the suspended regions exhibit higher local deformation compared to the supported areas, breaking the local symmetry and thereby activating otherwise forbidden or weak optical transitions of the VB- centers. △ Less

Submitted 31 August, 2025; originally announced September 2025.

Comments: 4 figures

Non-interacting fractional topological Stark insulator

Authors: Yi-Hong Chen, Si-Yuan Chen, Xin-Chi Zhou, Xiong-Jun Liu

Abstract: Fractional topological phases, such as the fractional quantum Hall state, usually rely on strong interactions to generate ground state degeneracy with gap protection and fractionalized topological response. Here, we propose a fractional topological phase without interaction in $(1+1)$-dimension, which is driven by the Stark localization on top of topological flat bands, different from the conventi… ▽ More Fractional topological phases, such as the fractional quantum Hall state, usually rely on strong interactions to generate ground state degeneracy with gap protection and fractionalized topological response. Here, we propose a fractional topological phase without interaction in $(1+1)$-dimension, which is driven by the Stark localization on top of topological flat bands, different from the conventional mechanism of the strongly correlated fractional topological phases. A linear potential gradient applied to the flat bands drives the Stark localization, under which the Stark localized states may hybridize and leads to a new gap in the real space, dubbed the real space energy gap (RSEG). Unlike the integer topological band insulator obtained in the weak linear potential regime without closing the original bulk gap, the fractional topological Stark insulating phase is resulted from the RSEG when the linear potential gradient exceeds a critical value. We develop a theoretical formalism to characterize the fractional topological Stark insulator, and further show that the many-body state under topological pumping returns to the initial state only after multiple $2π$ periods of evolution, giving the fractional charge pumping, similar to that in fractional quantum Hall state. Finally, we propose how to realize the fractional topological Stark insulator in real experiment. △ Less

Submitted 29 July, 2025; originally announced July 2025.

$d+1$ Measurement Bases are Sufficient for Determining $d$-Dimensional Quantum States: Theory and Experiment

Authors: Tianqi Xiao, Yaxin Wang, Ying Xia, Zhihao Li, Xiaoqi Zhou

Abstract: A long-standing problem in quantum physics is to determine the minimal number of measurement bases required for the complete characterization of unknown quantum states, a question of particular relevance to high-dimensional quantum information processing. Here, we propose a quantum state tomography scheme that requires only $d+1$ projective measurement bases to fully reconstruct an arbitrary $d$-d… ▽ More A long-standing problem in quantum physics is to determine the minimal number of measurement bases required for the complete characterization of unknown quantum states, a question of particular relevance to high-dimensional quantum information processing. Here, we propose a quantum state tomography scheme that requires only $d+1$ projective measurement bases to fully reconstruct an arbitrary $d$-dimensional quantum state. As a proof-of-principle, we experimentally verified this scheme on a silicon photonic chip by reconstructing quantum states for $d=6$, in which a complete set of mutually unbiased bases does not exist. This approach offers new perspectives for quantum state characterization and measurement design, and holds promise for future applications in quantum information processing. △ Less

Submitted 10 August, 2025; v1 submitted 15 July, 2025; originally announced July 2025.

Enhancing Photon Indistinguishability of Spectrally Mismatched Single Photons by Cavity Floquet Engineering

Authors: J. W. Yu, X. Q. Zhou, Z. B. Ni, X. T. Cheng, Y. Zhao, H. H. Zhu, C. H. Li, F. Liu, C. Y. Jin

Abstract: We theoretically propose a scheme to enhance the photon indistinguishability of spectrally mismatched single photons via Floquet-engineered optical frequency combs (OFCs) in cavity quantum electrodynamic systems. By periodically modulating two distinct single-photon states under a modulation frequency which is exactly equal to the spectral mismatch of two cavity modes, a pair of single-photon freq… ▽ More We theoretically propose a scheme to enhance the photon indistinguishability of spectrally mismatched single photons via Floquet-engineered optical frequency combs (OFCs) in cavity quantum electrodynamic systems. By periodically modulating two distinct single-photon states under a modulation frequency which is exactly equal to the spectral mismatch of two cavity modes, a pair of single-photon frequency-comb (SPFC) states is prepared energy-conservatively based on full unitary operations. The two states show high indistinguishability with an ideal $g^{(2)}_\mathrm{HOM}(0)$ down to zero due to the superposition of intensity-matched single-photon states coherently distributed across the teeth of the combs. △ Less

Submitted 3 July, 2025; originally announced July 2025.

Thermalization of Quantum Many-Body Scars in Kinetically Constrained Systems

Authors: Jia-wei Wang, Xiang-Fa Zhou, Guang-Can Guo, Zheng-Wei Zhou

Abstract: The phenomenon of quantum many-body scars (QMBS) has been studied both theoretically and experimentally, due to its unusual violation of the eigenstate thermalization hypothesis (ETH). In this paper, we extend the ETH to a new description based on the grand canonical ensemble to depict the thermal properties of QMBS models. For this purpose, we embed the dynamics of kinetically constrained systems… ▽ More The phenomenon of quantum many-body scars (QMBS) has been studied both theoretically and experimentally, due to its unusual violation of the eigenstate thermalization hypothesis (ETH). In this paper, we extend the ETH to a new description based on the grand canonical ensemble to depict the thermal properties of QMBS models. For this purpose, we embed the dynamics of kinetically constrained systems within the Lindblad-like master equation, and demonstrate that the violation of the ETH by scar eigenstates is related to their slow decay in the corresponding dissipative process. Within this open system description, we reformulate the ETH to demonstrate that both scar eigenstates and thermal ones exhibit thermalization governed by grand canonical statistics. Consequently, our revised ETH unifies scars and thermal states under a cohesive thermodynamic rule. Our work resolves the fundamental tension between constraint-induced non-ergodicity and thermalization paradigms, establishing a unified route to generalized thermalization for quantum many-body systems. △ Less

Submitted 24 June, 2025; v1 submitted 23 June, 2025; originally announced June 2025.

Comments: main manuscript with 7 pages containing 4 figures, complementary material with 8 pages containing 3 figures

NbTiN Nanowire Resonators for Spin-Photon Coupling on Solid Neon

Authors: Y. Tian, I. Grytsenko, A. Jennings, J. Wang, H. Ikegami, X. Zhou, S. Tamate, H. Terai, H. Kutsuma, D. Jin, M. Benito, E. Kawakami

Abstract: Electrons floating on a solid neon exhibit long charge coherence times, making them attractive for hybrid quantum systems. When combined with high-quality, high-impedance superconducting resonators and a local magnetic field gradient, this platform enables strong charge--photon and spin--charge coupling-key ingredients for scalable spin qubit architectures. In this work, we demonstrate that NbTiN… ▽ More Electrons floating on a solid neon exhibit long charge coherence times, making them attractive for hybrid quantum systems. When combined with high-quality, high-impedance superconducting resonators and a local magnetic field gradient, this platform enables strong charge--photon and spin--charge coupling-key ingredients for scalable spin qubit architectures. In this work, we demonstrate that NbTiN nanowire resonators maintain high quality factors around 10^5 after depositing solid neon onto the resonators and subsequently loading electrons onto the neon surface, validating their suitability for electrons-on-neon platforms. Building on these experimental results, we theoretically analyze micromagnet designs and coupling strategies that can enable spin-photon interactions in this platform. Our analysis outlines performance targets for next-generation devices, showing that, at the charge sweet spot, spin qubit gate fidelities exceeding 99.99% for single-qubit operations and 99.9% for two-qubit operations are achievable with natural neon. △ Less

Submitted 17 October, 2025; v1 submitted 30 May, 2025; originally announced May 2025.

Comments: 12 pages, 9 figures, submitted to Physical Review Applied

Quantitative calibration of a TWPA applied to an optomechanical platform

Authors: Alexandre Delattre, Ilya Golokolenov, Richard Pedurand, Nicolas Roch, Arpit Ranadive, Martina Esposito, Luca Planat, Andrew Fefferman, Eddy Collin, Xin Zhou, Mika A. Sillanpaa, Laure Mercier de Lepinay, Andrew D. Armour, Jonas Glatthard

Abstract: In the last decade, the microwave quantum electronics toolbox has been enriched with quantum-limited detection devices such as Traveling Wave Parametric Amplifiers (TWPAs). The extreme sensitivity they provide is not only mandatory for some physics applications within quantum information processing, but is also the key element that will determine the detection limit of quantum sensing setups. In t… ▽ More In the last decade, the microwave quantum electronics toolbox has been enriched with quantum-limited detection devices such as Traveling Wave Parametric Amplifiers (TWPAs). The extreme sensitivity they provide is not only mandatory for some physics applications within quantum information processing, but is also the key element that will determine the detection limit of quantum sensing setups. In the framework of microwave optomechanical systems, an unprecedented range of small motions and forces is accessible, for which a specific quantitative calibration becomes necessary. We report on near quantum-limited measurements performed with an aluminum drumhead mechanical device within the temperature range 4 mK - 400 mK. The whole setup is carefully calibrated, especially taking into account the power-dependence of microwave absorption in the superconducting optomechanical cavity. This effect is commonly attributed to Two-Level-Systems (TLSs) present in the metal oxide. We demonstrate that a similar feature exists in the TWPA, and can be phenomenologically fit with adapted expressions. If not taken into account, the error on the signal strength can be as large as a factor of about 2, which is unacceptable for quantitative experiments. The power and temperature dependence is studied over the full parameter range, leading to an absolute definition of phonon population (i.e. Brownian motion amplitude), with an uncertainty +- 20 % limited by sources of noise internal to the optomechanical element. △ Less

Submitted 13 November, 2025; v1 submitted 9 May, 2025; originally announced May 2025.

Journal ref: Phys. Rev. Applied Vol. 24, 054032 (2025)

Experimental Side-Channel-Secure Quantum Key Distribution over 200 km

Authors: Yang Zhou, Jing-Yang Liu, Chun-Hui Zhang, Hua-Jian Ding, Xing-Yu Zhou, Jian Li, Qin Wang

Abstract: Quantum key distribution enables two remote parties to share encryption keys with information-theoretic security based on physical laws. Side-channel-secure quantum key distribution (SCS-QKD) has attracted considerable attention due to its immunity to both source and detector side-channel attacks. Recently, a demonstration of SCS-QKD over 50 km has been realized. However, practical implementation… ▽ More Quantum key distribution enables two remote parties to share encryption keys with information-theoretic security based on physical laws. Side-channel-secure quantum key distribution (SCS-QKD) has attracted considerable attention due to its immunity to both source and detector side-channel attacks. Recently, a demonstration of SCS-QKD over 50 km has been realized. However, practical implementation of this protocol faces significant challenges, including the presence of an imperfect vacuum state and coherent attacks involving a limited number of pulses. Here, based on the theoretical work of Jiang et al. [Phys. Rev. Research 6, 013266 (2024)], we experimentally implemented the practical SCS-QKD protocol using an imperfect whole-space source. This allows us to extend the transmission distance to 200 km using fiber spools, achieving a secure key rate of 1.29E-7 bits per pulse while accounting for finite-key effects. These results establish a new distance record for SCS-QKD and highlight its potential for practical applications. We anticipate that this work will advance the practical implementation and security of quantum key distribution. △ Less

Submitted 6 May, 2025; originally announced May 2025.

Entanglement-Enhanced Nanoscale Single-Spin Sensing

Authors: Xu Zhou, Mengqi Wang, Xiangyu Ye, Haoyu Sun, Yuhang Guo, Han Shuo, Zihua Chai, Wentao Ji, Kangwei Xia, Fazhan Shi, Ya Wang, Jiangfeng Du

Abstract: Detecting individual spins--including stable and metastable states--represents a fundamental challenge in quantum sensing with broad applications across condensed matter physics, quantum chemistry, and single-molecule magnetic resonance imaging. While nitrogen-vacancy (NV) centers in diamond have emerged as powerful nanoscale sensors, their performance for single-spin detection remains constrained… ▽ More Detecting individual spins--including stable and metastable states--represents a fundamental challenge in quantum sensing with broad applications across condensed matter physics, quantum chemistry, and single-molecule magnetic resonance imaging. While nitrogen-vacancy (NV) centers in diamond have emerged as powerful nanoscale sensors, their performance for single-spin detection remains constrained by substantial environmental noise and restricted sensing volume. Here, we propose and demonstrate an entanglement-enhanced sensing protocol that overcomes these limitations through the strategic use of entangled NV pairs. Our approach achieves a 3.4-fold enhancement in sensitivity and a 1.6-fold reduction in spatial resolution relative to single NV centers under ambient conditions. The protocol employs carefully engineered entangled states that amplify target spin signals through quantum interference while suppressing environmental noise. Crucially, we extend these capabilities to resolve metastable single-spin dynamics, directly observing stochastic transitions between different spin states by identifying state-dependent coupling strengths. This dual functionality enables simultaneous detection of static and dynamic spin species for studying complex quantum systems. The achieved performance establishes entanglement-enhanced sensing as a viable pathway toward atomic-scale characterization of quantum materials and interface. △ Less

Submitted 30 April, 2025; originally announced April 2025.

Room-Temperature Hybrid 2D-3D Quantum Spin System for Enhanced Magnetic Sensing and Many-Body Dynamics

Authors: Haoyu Sun, Pei Yu, Xu Zhou, Xiangyu Ye, Mengqi Wang, Zhaoxin Liu, Yuhang Guo, Wenzhao Liu, You Huang, Pengfei Wang, Fazhan Shi, Kangwei Xia, Ya Wang

Abstract: Advances in hybrid quantum systems and their precise control are pivotal for developing advanced quantum technologies. Two-dimensional (2D) materials with optically accessible spin defects have emerged as a promising platform for building integrated quantum spin systems due to their exceptional flexibility and scalability. However, experimentally realizing such systems and demonstrating their supe… ▽ More Advances in hybrid quantum systems and their precise control are pivotal for developing advanced quantum technologies. Two-dimensional (2D) materials with optically accessible spin defects have emerged as a promising platform for building integrated quantum spin systems due to their exceptional flexibility and scalability. However, experimentally realizing such systems and demonstrating their superiority remains challenging. Here, we present a hybrid spin system operating under ambient conditions, integrating boron vacancy (VB) spins in 2D hexagonal boron nitride flakes with a single nitrogen vacancy (NV) center in 3D single-crystal diamonds. This combined system achieves full controllability and exhibits enhanced performance for nanoscale magnetic sensing, including an improved dynamic range. Moreover, we investigate the rich many-body spin dynamics within the hybrid system, enabling the first-time quantification of the fluorescence intensity of a single VB defect at 104 counts per second. This result represents a critical step toward the direct optical observation of single VB defects. △ Less

Submitted 14 April, 2025; originally announced April 2025.

The fundamental localization phases in quasiperiodic systems: A unified framework and exact results

Authors: Xin-Chi Zhou, Bing-Chen Yao, Yongjian Wang, Yucheng Wang, Yudong Wei, Qi Zhou, Xiong-Jun Liu

Abstract: The disordered quantum systems host three types of quantum states, the extended, localized, and critical, which bring up seven distinct fundamental phases in nature: three pure phases and four coexisting ones with mobility edges, yet a unified theory with full characterization and realization of all these phases has not been developed. Here we propose a complete and unified framework based on a sp… ▽ More The disordered quantum systems host three types of quantum states, the extended, localized, and critical, which bring up seven distinct fundamental phases in nature: three pure phases and four coexisting ones with mobility edges, yet a unified theory with full characterization and realization of all these phases has not been developed. Here we propose a complete and unified framework based on a spinful quasiperiodic (QP) system which realizes all the fundamental localization phases, with the exact and universal results being obtained for their characterization. First, we show that the pure phases are obtained when the chiral symmetry preserves in the proposed spinful QP model, giving a criterion for the emergence of the pure phases and otherwise the coexisting ones. Further, we uncover a novel universal mechanism for the critical states that their emergence is protected by the generalized incommensurate matrix element zeros in the spinful QP model, which considerably broadens the rigorous realizations of the exotic critical states. We then show the criteria of exact solvability for the present spinful QP system, with which we construct various exactly solvable models for all distinct localization phases. In particular, we propose two novel models, dubbed spin-selective QP lattice model and QP optical Raman lattice model, to achieve all basic types of mobility edges and all the seven fundamental phases of Anderson localization physics, respectively. The experimental scheme is proposed and studied in detail to realize these models with high feasibility. This study establishes a complete and profound theoretical framework which enables an in-depth exploration of the broad classes of all fundamental localization phenomena in QP systems, and offers key insights for constructing their exactly solvable models with experimental feasibility. △ Less

Submitted 29 May, 2025; v1 submitted 31 March, 2025; originally announced March 2025.

Comments: 24 pages, 8 figures. The discussion has been significantly expanded, and a new appendix and an additional figure have been added

Coherent manipulation of interacting electron qubits on solid neon

Authors: Xinhao Li, Yizhong Huang, Xu Han, Xianjing Zhou, Amir Yacoby, Dafei Jin

Abstract: Solid neon has recently emerged as a pristine material host for electron qubits. Single electron-on-solid-neon (eNe) charge qubits have shown extraordinarily long coherence times and high operation fidelities. Realizing two-qubit gates in this platform is the next major step for practical quantum information processing. In this work, we demonstrate frequency- and time-domain coherent manipulation… ▽ More Solid neon has recently emerged as a pristine material host for electron qubits. Single electron-on-solid-neon (eNe) charge qubits have shown extraordinarily long coherence times and high operation fidelities. Realizing two-qubit gates in this platform is the next major step for practical quantum information processing. In this work, we demonstrate frequency- and time-domain coherent manipulation of multiple eNe charge qubits that are coupled by charge-charge interactions. Cross-resonance and bSWAP two-qubit gates are implemented, laying the foundation for universal quantum computing. Inter-qubit coupling strength exceeding 60~MHz is observed, promising fast and high-fidelity two-qubit gates. These results highlight the potential to develop the eNe qubit platform into a compelling quantum computing architecture. △ Less

Submitted 24 August, 2025; v1 submitted 31 March, 2025; originally announced March 2025.

Collective emission and selective radiance in atomic clouds and arrays coupled to a microring resonator

Authors: Deepak A. Suresh, Xinchao Zhou, Chen-Lung Hung, F. Robicheaux

Abstract: We theoretically investigate the collective dipole-dipole interactions in atoms coupled to a nanophotonic microring resonator. The atoms can interact with each other through light-induced dipole-dipole interactions mediated by free space and through the resonator whispering-gallery modes. The differing characteristics and mismatched wavenumbers of these modes give rise to complex dynamics and prov… ▽ More We theoretically investigate the collective dipole-dipole interactions in atoms coupled to a nanophotonic microring resonator. The atoms can interact with each other through light-induced dipole-dipole interactions mediated by free space and through the resonator whispering-gallery modes. The differing characteristics and mismatched wavenumbers of these modes give rise to complex dynamics and provide new opportunities for controlling light-matter interactions. We explore these phenomena in the context of an experimentally realized atom cloud and study the potential of the proposed sub-wavelength atom arrays. △ Less

Submitted 27 October, 2025; v1 submitted 26 March, 2025; originally announced March 2025.

Comments: 12 pages, 7 figures

Journal ref: Phys. Rev. A 112, 043717 (2025)

Exploring the boundary of quantum network states from inside out

Authors: Xiang Zhou, Zhen-Peng Xu, Liang-Liang Sun, Chunfeng Wu, Sixia Yu

Abstract: Quantum networks with bipartite resources and shared randomness present the simplest infrastructure for implementing a future quantum internet. Here, we shall investigate which kinds of entanglement can or cannot be generated from this kind of quantum network by examining their fidelity with different graph states. On the one hand, based on a standard form of graph states under local complementati… ▽ More Quantum networks with bipartite resources and shared randomness present the simplest infrastructure for implementing a future quantum internet. Here, we shall investigate which kinds of entanglement can or cannot be generated from this kind of quantum network by examining their fidelity with different graph states. On the one hand, based on a standard form of graph states under local complementation and a fine-grained uncertainty relation between two projections, we establish upper bounds of fidelity that improve over previous results by at least $25\%$ as the dimension of local systems tends to infinity. On the other hand, in the triangle network, we propose efficient protocols to generate genuine multipartite entangled states from the network, providing significant nontrivial lower bounds of fidelity with high dimensional GHZ states. △ Less

Submitted 12 March, 2025; originally announced March 2025.

Comments: 5+8 page, 10 figures. See also the related work by Justus Neumann et al. in today's arXiv listing

Selective collective emission from a dense atomic ensemble coupled to a nanophotonic resonator

Authors: Xinchao Zhou, Deepak A. Suresh, F. Robicheaux, Chen-Lung Hung

Abstract: We experimentally and theoretically study collective emission of a dense atomic ensemble coupled to a single mode in a nanophotonic microring resonator. Because many cold atoms are localized in a small volume, these trapped atoms collectively couple not only to the guided resonator mode but also to the nonguided modes in free space. Through tuning the atom-photon coupling and by adjusting the numb… ▽ More We experimentally and theoretically study collective emission of a dense atomic ensemble coupled to a single mode in a nanophotonic microring resonator. Because many cold atoms are localized in a small volume, these trapped atoms collectively couple not only to the guided resonator mode but also to the nonguided modes in free space. Through tuning the atom-photon coupling and by adjusting the number of trapped atoms, we demonstrate superradiant emission to the microring resonator. For photon emission via the nonguided modes, our study reveals signatures of subradiance and superradiance when the system is driven to the steady state and to the timed-Dicke state, respectively. Our experimental platform thus presents the first atom-light interface with selective collective emission behavior into a guided mode and the environment. Our observation and methodology could shed light on future explorations of collective emission with densely packed quantum emitters coupled to nanophotonic light-matter interfaces. △ Less

Submitted 10 September, 2025; v1 submitted 7 March, 2025; originally announced March 2025.

Comments: 13 pages, 9 figures

Journal ref: Phys. Rev. Lett. 135, 113601 (2025)

Hybrid Implementation for Untrusted-node-based Quantum Key Distribution Network

Authors: Jingyang Liu, Xingyu Zhou, Huajian Ding, Jiaxin Xu, Chunhui Zhang, Jian Li, Qin Wang

Abstract: Quantum key distribution (QKD) serves as a cornerstone of secure quantum communication, providing unconditional security grounded in quantum mechanics. While trusted-node networks have facilitated early QKD deployment, their vulnerability to node compromise underscores the need for untrusted-node architectures. Measurement-device-independent QKD (MDI-QKD) and twin-field QKD (TF-QKD) have emerged a… ▽ More Quantum key distribution (QKD) serves as a cornerstone of secure quantum communication, providing unconditional security grounded in quantum mechanics. While trusted-node networks have facilitated early QKD deployment, their vulnerability to node compromise underscores the need for untrusted-node architectures. Measurement-device-independent QKD (MDI-QKD) and twin-field QKD (TF-QKD) have emerged as leading candidates, addressing security vulnerabilities and extending transmission distances. Despite the wide adoptions in various fiber scaling, no integrated implementation of these two protocols has been demonstrated to date. Here, we present a hybrid system that seamlessly integrates TF-QKD and MDI-QKD into one untrusted-node-based architecture. Utilizing an efficient phase estimation method based on asymmetric interferometers, we convert twin-field global phase tracking to relative phase calibration, allowing near continuous running of both protocols. Experiments demonstrate secure finite-size key rates for sending-or-not-sending QKD and MDI-QKD over fiber distances of 150 to 431 km. The results align with theoretical simulations and show the ability to surpass the absolute repeaterless key capacity. Our work offers an unified framework for deploying multi-protocol QKD networks, laying the foundation for adaptable and scalable quantum infrastructures that can meet a wide range of security and performance needs. △ Less

Submitted 6 March, 2025; originally announced March 2025.

SSR: A Swapping-Sweeping-and-Rewriting Optimizer for Quantum Circuit Transformation

Authors: Yunqi Huang, Xiangzhen Zhou, Fanxu Meng, Pengcheng Zhu, Yu Luo, Zhenlong Du

Abstract: Quantum circuit transformation (QCT), necessary for adapting any quantum circuit to the qubit connectivity constraints of the NISQ device, often introduces numerous additional SWAP gates into the original circuit, increasing the circuit depth and thus reducing the success rate of computation. To minimize the depth of QCT circuits, we propose a Swapping-Sweeping-and-Rewriting optimizer. This optimi… ▽ More Quantum circuit transformation (QCT), necessary for adapting any quantum circuit to the qubit connectivity constraints of the NISQ device, often introduces numerous additional SWAP gates into the original circuit, increasing the circuit depth and thus reducing the success rate of computation. To minimize the depth of QCT circuits, we propose a Swapping-Sweeping-and-Rewriting optimizer. This optimizer rearranges the circuit based on generalized gate commutation rules via a genetic algorithm, extracts subcircuits consisting of CNOT gates using a circuit sweeping technique, and rewrites each subcircuit with a functionally equivalent and depth-optimal circuit generated by an SAT solver. The devised optimizer effectively captures the intrinsic patterns of the QCT circuits, and the experimental results demonstrate that our algorithm can significantly reduce the depth of QCT circuits, 26.68\% at most and 12.18\% on average, across all benchmark circuits. △ Less

Submitted 23 October, 2025; v1 submitted 5 March, 2025; originally announced March 2025.

Comments: The change in experimental data is due to the improvement of program code

Nonreciprocal Entanglement by Dynamically Encircling a Nexus

Authors: Lei Huang, Peng-Fei Wang, Jian-Qi Zhang, Xin Zhou, Shuo Zhang, Han-Xiao Zhang, Hong Yang, Dong Yan

Abstract: Nonreciprocal entanglement, characterized by inherently robust operation, is a cornerstone for quantum information processing and communications. However, it remains a great challenge to achieve nonreciprocal entanglement characterized by stability and robustness against environmental fluctuations. Here, we propose a universal nonlinear mechanism to engineer magnetic-free nonreciprocity in dissipa… ▽ More Nonreciprocal entanglement, characterized by inherently robust operation, is a cornerstone for quantum information processing and communications. However, it remains a great challenge to achieve nonreciprocal entanglement characterized by stability and robustness against environmental fluctuations. Here, we propose a universal nonlinear mechanism to engineer magnetic-free nonreciprocity in dissipative optomechanics by utilizing bistability, a phenomenon ubiquitous across nonlinear physical systems. By dynamically encircling the nexus of bistability, a cusp converged by the bistable surfaces, we obtain nonreciprocal displacement and then utilize it to achieve robust nonreciprocal entanglement. Owing to the unique landscape of bistability, our nonreciprocal displacement and entanglements exhibit stability and robustness through closed-loop operations. Our work presents a foundational framework for leveraging nonlinearity to achieve nonreciprocal quantum information processing. It paves new avenues for exploring nonreciprocal quantum information processing and designing backaction-immune quantum metrology with nonlinearity. △ Less

Submitted 30 August, 2025; v1 submitted 26 February, 2025; originally announced February 2025.

Comments: 8 pages, 4 figures

Exact quantum critical states with a superconducting quantum processor

Authors: Wenhui Huang, Xin-Chi Zhou, Libo Zhang, Jiawei Zhang, Yuxuan Zhou, Bing-Chen Yao, Zechen Guo, Peisheng Huang, Qixian Li, Yongqi Liang, Yiting Liu, Jiawei Qiu, Daxiong Sun, Xuandong Sun, Zilin Wang, Changrong Xie, Yuzhe Xiong, Xiaohan Yang, Jiajian Zhang, Zihao Zhang, Ji Chu, Weijie Guo, Ji Jiang, Xiayu Linpeng, Wenhui Ren , et al. (7 additional authors not shown)

Abstract: Anderson localization physics features three fundamental types of eigenstates: extended, localized, and critical. Confirming the presence of critical states necessitates either advancing the analysis to the thermodynamic limit or identifying a universal mechanism which can rigorously determine these states. Here we report the unambiguous experimental realization of critical states, governed by a r… ▽ More Anderson localization physics features three fundamental types of eigenstates: extended, localized, and critical. Confirming the presence of critical states necessitates either advancing the analysis to the thermodynamic limit or identifying a universal mechanism which can rigorously determine these states. Here we report the unambiguous experimental realization of critical states, governed by a rigorous mechanism for exact quantum critical states, and further observe a generalized mechanism that quasiperiodic zeros in hopping couplings protect the critical states. Leveraging a superconducting quantum processor with up to 56 qubits, we implement a programmable mosaic model with tunable couplings and on-site potentials. By measuring time-evolved observables, we identify both delocalized dynamics and incommensurately distributed zeros in the couplings, which are the defining features of the critical states. We map the localized-to-critical phase transition and demonstrate that critical states persist until quasiperiodic zeros are removed by strong long-range couplings, highlighting a novel generalized mechanism discovered in this experiment and shown with rigorous theory. Finally, we resolve the energy-dependent transition between localized and critical states, revealing the presence of anomalous mobility edges. △ Less

Submitted 25 March, 2025; v1 submitted 26 February, 2025; originally announced February 2025.

Comments: 6+29 pages, 4+14 figures. Discussions are updated

Noise-resilient solid host for electron qubits above 100 mK

Authors: Xinhao Li, Christopher S. Wang, Brennan Dizdar, Yizhong Huang, Yutian Wen, Wei Guo, Xufeng Zhang, Xu Han, Xianjing Zhou, Dafei Jin

Abstract: Cryogenic solid neon has recently emerged as a pristine solid host for single electron qubits. At ~10 mK temperatures, electron-on-solid-neon (eNe) charge qubits have exhibited exceptionally long coherence times and high operation fidelities. To advance this platform towards a scalable quantum information architecture, systematic characterization of its noise feature is imperative. Here, we show t… ▽ More Cryogenic solid neon has recently emerged as a pristine solid host for single electron qubits. At ~10 mK temperatures, electron-on-solid-neon (eNe) charge qubits have exhibited exceptionally long coherence times and high operation fidelities. To advance this platform towards a scalable quantum information architecture, systematic characterization of its noise feature is imperative. Here, we show the remarkable resilience of solid neon against charge and thermal noises when eNe qubits are operated away from the charge-insensitive sweet-spot and at elevated temperatures. Without optimizing neon growth, the measured charge (voltage) noise on solid neon is already orders of magnitude lower than that in most stringently grown semiconductors, rivaling the best records to date. Up to 400 mK, the eNe charge qubits operated at ~5 GHz can maintain their echo coherence times over 1 microsecond. These observations highlight solid neon as an ideal host for quantum information processing at higher temperatures and larger scales. △ Less

Submitted 7 April, 2025; v1 submitted 2 February, 2025; originally announced February 2025.

Two measurement bases are asymptotically informationally complete for any pure state tomography

Authors: Tianfeng Feng, Tianqi Xiao, Yu Wang, Shengshi Pang, Farhan Hanif, Xiaoqi Zhou, Qi Zhao, M. S. Kim, Jinzhao Sun

Abstract: One of the fundamental questions in quantum information theory is to find how many measurement bases are required to obtain the full information of a quantum state. While a minimum of four measurement bases is typically required to determine an arbitrary pure state, we prove that for any states generated by finite-depth Clifford + T circuits, just two measurement bases are sufficient. More general… ▽ More One of the fundamental questions in quantum information theory is to find how many measurement bases are required to obtain the full information of a quantum state. While a minimum of four measurement bases is typically required to determine an arbitrary pure state, we prove that for any states generated by finite-depth Clifford + T circuits, just two measurement bases are sufficient. More generally, we prove that two measurement bases are informationally complete for determining algebraic pure states whose state-vector elements represented in the computational basis are algebraic numbers. Since any pure state can be asymptotically approximated by a sequence of algebraic states with arbitrarily high precision, our scheme is referred to as asymptotically informationally complete for pure state tomography. Furthermore, existing works mostly construct the measurements using entangled bases. So far, the best result requires $O(n)$ local measurement bases for $n$-qubit pure-state tomography. Here, we show that two measurement bases that involve polynomial elementary gates are sufficient for uniquely determining sparse algebraic states. Moreover, we prove that two local measurement bases, involving single-qubit local operations only, are informationally complete for certain algebraic states, such as GHZ-like and W-like states. Besides, our two-measurement-bases scheme remains valid for mixed states with certain types of noises. We numerically test the uniqueness of the reconstructed states under two (local) measurement bases with and without measurement and depolarising types of noise. Our scheme provides a theoretical guarantee for pure state tomography in the fault-tolerant quantum computing regime. △ Less

Submitted 28 January, 2025; originally announced January 2025.

Comments: 28 pages, 8 figures, 1 table

Quantum many-body dynamics for fermionic t-J model simulated with atom arrays

Authors: Ye-Bing Zhang, Xin-Chi Zhou, Bao-Zong Wang, Xiong-Jun Liu

Abstract: The fermionic t-J model has been widely recognized as a canonical model for broad range of strongly correlated phases, particularly the high-Tc superconductor. Simulating this model with controllable quantum platforms offers new possibilities to probe high-Tc physics, yet suffering challenges. Here we propose a novel scheme to realize a highly-tunable extended t-J model in a programmable Rydberg-d… ▽ More The fermionic t-J model has been widely recognized as a canonical model for broad range of strongly correlated phases, particularly the high-Tc superconductor. Simulating this model with controllable quantum platforms offers new possibilities to probe high-Tc physics, yet suffering challenges. Here we propose a novel scheme to realize a highly-tunable extended t-J model in a programmable Rydberg-dressed tweezer array. Through engineering the Rydberg-dressed dipole-dipole interaction and inter-tweezer couplings, the fermionic t-J model with independently tunable exchange and hopping couplings is achieved. With the high tunability, we explore quantum many-body dynamics in the large J/t limit, a regime well beyond the conventional optical lattices and cuprates, and predict an unprecedented many-body self-pinning effect enforced by local quantum entanglement with emergent conserved quantities. The self-pinning effect leads to novel nonthermal quantum many-body dynamics, which violates eigenstate thermalization hypothesis in Krylov subspace. Our prediction opens a new horizon in exploring exotic quantum many-body physics with t-J model, and shall also make a step towards simulating the high-Tc physics in neutral atom systems. △ Less

Submitted 8 July, 2025; v1 submitted 31 December, 2024; originally announced January 2025.

Comments: 24 pages, 11 figures, updates have been made according to the feedback from referees

Efficient Evaluation of Optical Quantum Modules via Two-Photon High-Dimensional Interference

Authors: Xiaoqian Zhang, Maolin Luo, Xiaoqi Zhou

Abstract: The rapid advancement of quantum information technology has increased the demand for precise testing and calibration of quantum modules, especially in optical quantum circuits where module reliability directly impacts system performance. To address this need, we propose a two-photon quantum module evaluation method based on high-dimensional Hong-Ou-Mandel interference. Our method uses multi-degree… ▽ More The rapid advancement of quantum information technology has increased the demand for precise testing and calibration of quantum modules, especially in optical quantum circuits where module reliability directly impacts system performance. To address this need, we propose a two-photon quantum module evaluation method based on high-dimensional Hong-Ou-Mandel interference. Our method uses multi-degree-of-freedom photon encoding to enable rapid and accurate evaluation of optical quantum modules. Compared to traditional methods such as quantum process tomography and direct fidelity estimation, our method not only simplifies implementation but also significantly minimizes the measurement resources required. Notably, the resource demands remain invariant as the system dimensionality scales, ensuring efficient evaluation even in high-dimensional quantum systems. We validated this method on a programmable silicon photonic chip, demonstrating its ability to accurately evaluate optical quantum module performance while significantly reducing resource consumption. This quantum module evaluation method holds promise for broader applications in the field of optical quantum information technologies. △ Less

Submitted 9 January, 2025; v1 submitted 28 December, 2024; originally announced December 2024.

MSC Class: 81S05 ACM Class: C.2

Hiding, Shuffling, and Cycle Finding: Quantum Algorithms on Edge Lists

Authors: Amin Shiraz Gilani, Daochen Wang, Pei Wu, Xingyu Zhou

Abstract: The edge list model is arguably the simplest input model for graphs, where the graph is specified by a list of its edges. In this model, we study the quantum query complexity of three variants of the triangle finding problem. The first asks whether there exists a triangle containing a target edge and raises general questions about the hiding of a problem's input among irrelevant data. The second a… ▽ More The edge list model is arguably the simplest input model for graphs, where the graph is specified by a list of its edges. In this model, we study the quantum query complexity of three variants of the triangle finding problem. The first asks whether there exists a triangle containing a target edge and raises general questions about the hiding of a problem's input among irrelevant data. The second asks whether there exists a triangle containing a target vertex and raises general questions about the shuffling of a problem's input. The third asks whether there exists a triangle; this problem bridges the $3$-distinctness and $3$-sum problems, which have been extensively studied by both cryptographers and complexity theorists. We provide tight or nearly tight results for these problems as well as some first answers to the general questions they raise. Furthermore, given any graph with low maximum degree, such as a typical random sparse graph, we prove that the quantum query complexity of finding a length-$k$ cycle in its length-$m$ edge list is $m^{3/4-1/(2^{k+2}-4)\pm o(1)}$, which matches the best-known upper bound for the quantum query complexity of $k$-distinctness on length-$m$ inputs up to an $m^{o(1)}$ factor. We prove the lower bound by developing new techniques within Zhandry's recording query framework [CRYPTO '19] as generalized by Hamoudi and Magniez [ToCT '23]. These techniques extend the framework to treat any non-product distribution that results from conditioning a product distribution on the absence of rare events. We prove the upper bound by adapting Belovs's learning graph algorithm for $k$-distinctness [FOCS '12]. Finally, assuming a plausible conjecture concerning only cycle finding, we show that the lower bound can be lifted to an essentially tight lower bound on the quantum query complexity of $k$-distinctness, which is a long-standing open question. △ Less

Submitted 12 November, 2025; v1 submitted 23 December, 2024; originally announced December 2024.

Comments: 80 pages; v2: major update to include new results on cycle finding; v3: corrected Mirroring Lemma and improved presentation

Scattering halos in strongly interacting Feshbach molecular Bose-Einstein condensates

Authors: Yuying Chen, Zhengxi Zhang, Chi-Kin Lai, Yun Liang, Hongmian Shui, Haixiang Fu, Fansu Wei, Xiaoji Zhou

Abstract: We investigate the scattering halos resulting from collisions between discrete momentum components in the time-of-flight expansion of interaction-tunable $^6\rm Li_2$ molecular Bose-Einstein condensates. A key highlight of this study is the observation of the influence of interactions on the collisional scattering process. We measure the production of scattering halos at different interaction leve… ▽ More We investigate the scattering halos resulting from collisions between discrete momentum components in the time-of-flight expansion of interaction-tunable $^6\rm Li_2$ molecular Bose-Einstein condensates. A key highlight of this study is the observation of the influence of interactions on the collisional scattering process. We measure the production of scattering halos at different interaction levels by varying the number of particles and the scattering length, and quantitatively assess the applicability of perturbation theory. To delve into a general theory of scattering halos, we introduce a scattering factor and obtain a universal relation between it and the halo ratio. Furthermore, we simulate the formation of scattering halos under non-perturbative conditions and analyze the discrepancies between simulation results and experiments through a return pulse experiment. This study enhances our understanding of the physical mechanisms underlying scattering processes in many-body systems and provides new perspectives for further theoretical research. △ Less

Submitted 23 December, 2024; originally announced December 2024.

Journal ref: Phys. Rev. A 111, 043303 (2025)

Ultrafast high-fidelity state readout of single neutral atom

Authors: Jian Wang, Dong-Yu Huang, Xiao-Long Zhou, Ze-Min Shen, Si-Jian He, Qi-Yang Huang, Yi-Jia Liu, Chuan-Feng Li, Guang-Can Guo

Abstract: The capability to measure the state of a quantum system is vital to a practical quantum network, for applications including distributed quantum computing and long-distance quantum communication. As a thriving platform for quantum information technology, single neutral atoms suffer from low achievable photon scattering rate and shallow trapping potential, which limits the fidelity and speed of stat… ▽ More The capability to measure the state of a quantum system is vital to a practical quantum network, for applications including distributed quantum computing and long-distance quantum communication. As a thriving platform for quantum information technology, single neutral atoms suffer from low achievable photon scattering rate and shallow trapping potential, which limits the fidelity and speed of state readout process. Here, by coupling an single neutral atom with a high-finesse fiber-based Fabry-Pérot microcavity (FFPC) in Purcell regime, we realize strong enhancement of the atomic photoemission rate, which enables ultrafast and high-fidelity discrimination of bright and dark hyperfine states of the atom. The readout fidelity can reach 99.1(2)% within 200 ns and 99.985(8)% within 9 $μ$s. Furthermore, we demonstrate that state preparation via optical pumping can be efficiently accelerated by real-time decision protocol based on ultrafast state readout. This work paves the way to the implementation of quantum networking protocols with high communication rate and high fidelity. △ Less

Submitted 17 December, 2024; originally announced December 2024.

Comments: 9 pages, 9 figures, 53 references

Purcell-Enhanced Generation of Photonic Bell States via the Inelastic Scattering of Single Atoms

Authors: Jian Wang, Xiao-Long Zhou, Ze-Min Shen, Dong-Yu Huang, Si-Jian He, Qi-Yang Huang, Yi-Jia Liu, Chuan-Feng Li, Guang-Can Guo

Abstract: Single atoms trapped in optical cavities exhibit immense potential as key nodes in future quantum information processing. They have already demonstrated significant advancement in various quantum technologies, particularly regarding the generation of nonclassical light. Here, we efficiently produce genuine photonic Bell states through the inelastic scattering process of single two-level intracavit… ▽ More Single atoms trapped in optical cavities exhibit immense potential as key nodes in future quantum information processing. They have already demonstrated significant advancement in various quantum technologies, particularly regarding the generation of nonclassical light. Here, we efficiently produce genuine photonic Bell states through the inelastic scattering process of single two-level intracavity atoms. An experimental violation of the Bell inequality, arising from the interference between the probability amplitudes of two photons, validates the intrinsic nature of energy-time entanglement. Coupling atoms with an optical cavity in the Purcell regime substantially enhances the two-photon scattering. This Bell state generation process does not require atomic spin control, thereby rendering it inherently immune to decoherence effects. This work advances the comprehension of resonance fluorescence and has the potential to broaden the landscape of quantum technologies and facilitate the application of photonic Bell states. △ Less

Submitted 16 December, 2024; originally announced December 2024.

Comments: 9 pages, 8 figures, 47 reference

Collisional scattering of strongly interacting D-band Feshbach molecules in optical lattices

Authors: Fansu Wei, Chi-Kin Lai, Yuying Chen, Zhengxi Zhang, Yun Liang, Hongmian Shui, Chen Li, Xiaoji Zhou

Abstract: The excited bands in optical lattices manifest an important tool for studying quantum simulation and many-body physics, making it crucial to measure high-band scattering dynamics under strong interactions. This work investigates both experimentally and theoretically the collisional scattering of $^{6}\rm Li_2$ molecular Bose-Einstein condensate in the $D$ band of a one-dimensional optical lattice,… ▽ More The excited bands in optical lattices manifest an important tool for studying quantum simulation and many-body physics, making it crucial to measure high-band scattering dynamics under strong interactions. This work investigates both experimentally and theoretically the collisional scattering of $^{6}\rm Li_2$ molecular Bose-Einstein condensate in the $D$ band of a one-dimensional optical lattice, with interaction strength directly tunable via magnetic Feshbach resonance. We find a clear dependence of the $D$-band lifetimes on the interaction strength within the strongly interacting regime, which arises from the fact that the scattering cross-section is proportional to the square of the scattering length. The maximum lifetime versus lattice depth is measured to reveal the effects of interactions. We also investigate the scattering channels of $D$-band molecules under different interaction levels and develop a reliable two-body scattering rate equation. This work provides insight into the interplay between interaction and the collisional scattering of high-band bosons in optical lattices, paving the way for research into strong correlation effects in high-band lattice systems. △ Less

Submitted 10 December, 2024; originally announced December 2024.

Journal ref: Phys. Rev. Research 7, 023030 (2025)

Topological Aspects of Dirac Fermions in a Kagomé Lattice

Authors: Xinyuan Zhou, Ziqiang Wang, Hua Chen

Abstract: The Dirac fermion with linear dispersion in the kagomé lattice governs the low-energy physics of different valleys at two inequivalent corners of hexagonal Brillouin zone. The effective Hamiltonian based on the cyclic permutation symmetry of sublattices is constructed to show that the topology of Dirac fermions at these two valleys is characterized by opposite winding numbers. For spinless fermion… ▽ More The Dirac fermion with linear dispersion in the kagomé lattice governs the low-energy physics of different valleys at two inequivalent corners of hexagonal Brillouin zone. The effective Hamiltonian based on the cyclic permutation symmetry of sublattices is constructed to show that the topology of Dirac fermions at these two valleys is characterized by opposite winding numbers. For spinless fermions, the many-particle interactions produce intervalley scattering and drive an intervalley coherent state with spontaneous translation symmetry breaking. The Dirac fermions acquire a mass term from the simultaneous charge and bond orderings. In this phase, the developed bond texture underlies a hollow-star-of-David pattern in a tripled Wigner-Seitz cell of kagomé lattice. It is further demonstrated that the twisting of Dirac mass with vorticity leads to zero Dirac modes at the vortex core, which are intimately related to fractionalization. The hollow-star-of-David phase is shown to have a distinct $\mathbb{Z}_6$ Berry phase with its sign-change counterpart of Dirac mass, i.e. the hexagonal phase, shedding light on the topological origin of zero Dirac modes around the vortex core. △ Less

Submitted 18 September, 2025; v1 submitted 5 December, 2024; originally announced December 2024.

Comments: 8 pages, 4 figures

Journal ref: Phys. Rev. B 112, 075117 (2025)

Bosonic Peierls state emerging from the one-dimensional Ising-Kondo interaction

Authors: Jingtao Fan, Xiaofan Zhou, Suotang Jia

Abstract: As an important effect induced by the particle-lattice interaction, the Peierls transition, a hot topic in condensed matter physics, is usually believed to occur in the one-dimensional fermionic systems. We here study a bosonic version of the one-dimensional Ising-Kondo lattice model, which describes itinerant bosons interact with the localized magnetic moments via only longitudinal Kondo exchange… ▽ More As an important effect induced by the particle-lattice interaction, the Peierls transition, a hot topic in condensed matter physics, is usually believed to occur in the one-dimensional fermionic systems. We here study a bosonic version of the one-dimensional Ising-Kondo lattice model, which describes itinerant bosons interact with the localized magnetic moments via only longitudinal Kondo exchange.\ We show that, by means of perturbation analysis and numerical density-matrix renormalization group method, a bosonic analog of the Peierls state can occur in proper parameters regimes. The Peierls state here is characterized by the formation of a long-range spin-density-wave order, the periodicity of which is set by the density of the itinerant bosons. The ground-state phase diagram is mapped out by extrapolating the finite-size results to thermodynamic limit. Apart from the bosonic Peierls state, we also reveal the presence of some other magnetic orders, including a paramagnetic phase and a ferromagnetic phase. We finally propose a possible experimental scheme with ultracold atoms in optical lattices. Our results broaden the frontiers of the current understanding of the one-dimensional particle-lattice interaction system. △ Less

Submitted 25 November, 2024; originally announced November 2024.

Comments: 12 pages, 11 figures

Journal ref: PhysRevB.111.06411 (2025)

Exact Quantum Algorithm for Unit Commitment Optimization based on Partially Connected Quantum Neural Networks

Authors: Jian Liu, Xu Zhou, Zhuojun Zhou, Le Luo

Abstract: The quantum hybrid algorithm has become a very promising and speedily method today for solving the larger-scale optimization in the noisy intermediate-scale quantum (NISQ) era. The unit commitment (UC) problem is a fundamental problem in the power system which aims to satisfy a balance load with minimal cost. In this paper, we focus on the implement of the UC-solving by exact quantum algorithms ba… ▽ More The quantum hybrid algorithm has become a very promising and speedily method today for solving the larger-scale optimization in the noisy intermediate-scale quantum (NISQ) era. The unit commitment (UC) problem is a fundamental problem in the power system which aims to satisfy a balance load with minimal cost. In this paper, we focus on the implement of the UC-solving by exact quantum algorithms based on the quantum neural network (QNN). This method is tested with up to 10-unit system with the balance load constraint. In order to improve the computing precision and reduce the network complexity, we suggest the knowledge-based partially connected quantum neural network (PCQNN). The results show that the exact solutions can be obtained by the improved algorithm and the depth of the quantum circuit can be reduced simultaneously. △ Less

Submitted 18 November, 2024; originally announced November 2024.

Report number: 100303

Journal ref: Chinese Physics B, 2025

Classifying extended, localized and critical states in quasiperiodic lattices via unsupervised learning

Authors: Bohan Zheng, Siyu Zhu, Xingping Zhou, Tong Liu

Abstract: Classification of quantum phases is one of the most important areas of research in condensed matter physics. In this work, we obtain the phase diagram of one-dimensional quasiperiodic models via unsupervised learning. Firstly, we choose two advanced unsupervised learning algorithms, Density-Based Spatial Clustering of Applications with Noise (DBSCAN) and Ordering Points To Identify the Clustering… ▽ More Classification of quantum phases is one of the most important areas of research in condensed matter physics. In this work, we obtain the phase diagram of one-dimensional quasiperiodic models via unsupervised learning. Firstly, we choose two advanced unsupervised learning algorithms, Density-Based Spatial Clustering of Applications with Noise (DBSCAN) and Ordering Points To Identify the Clustering Structure (OPTICS), to explore the distinct phases of Aubry-André-Harper model and quasiperiodic p-wave model. The unsupervised learning results match well with traditional numerical diagonalization. Finally, we compare the similarity of different algorithms and find that the highest similarity between the results of unsupervised learning algorithms and those of traditional algorithms has exceeded 98\%. Our work sheds light on applications of unsupervised learning for phase classification. △ Less

Submitted 19 October, 2024; originally announced October 2024.

Super-Heisenberg scaling in a triple point criticality

Authors: Jia-Ming Cheng, Yong-Chang Zhang, Xiang-Fa Zhou, Zheng-Wei Zhou

Abstract: We investigate quantum-enhanced metrology in a triple point criticality and discover that quantum criticality can not always enhance measuring precision. We have developed suitable adiabatic evolution protocols approaching a final point around the triple point to effectively restrain excitations, which could accelerate the adiabatic evolutions and lead to an exponential super-Heisenberg scaling. T… ▽ More We investigate quantum-enhanced metrology in a triple point criticality and discover that quantum criticality can not always enhance measuring precision. We have developed suitable adiabatic evolution protocols approaching a final point around the triple point to effectively restrain excitations, which could accelerate the adiabatic evolutions and lead to an exponential super-Heisenberg scaling. This scaling behavior is quite valuable in practical parameter estimating experiments with limited coherence time. The super-Heisenberg scaling will degrade into a sub-Heisenberg scaling if the adiabatic parameter modulations adopted can not reduce excitations and weaken the slowing down effect. Additionally, a feasible experimental scheme is also suggested to achieve the anticipated exponential super-Heisenberg scaling. Our findings strongly indicate that criticality-enhanced metrology can indeed significantly enhance measuring precision to a super-Heisenberg scaling when combining a triple point and beneficial parameter modulations in the adiabatic evolution, which will be conducive to the exploration of other super-Heisenberg scaling and their applications. △ Less

Submitted 31 March, 2025; v1 submitted 21 September, 2024; originally announced September 2024.

Qubit Mapping: The Adaptive Divide-and-Conquer Approach

Authors: Yunqi Huang, Xiangzhen Zhou, Fanxu Meng, Sanjiang Li

Abstract: The qubit mapping problem (QMP) focuses on the mapping and routing of qubits in quantum circuits so that the strict connectivity constraints imposed by near-term quantum hardware are satisfied. QMP is a pivotal task for quantum circuit compilation and its decision version is NP-complete. In this study, we present an effective approach called Adaptive Divided-And-Conqure (ADAC) to solve QMP. Our AD… ▽ More The qubit mapping problem (QMP) focuses on the mapping and routing of qubits in quantum circuits so that the strict connectivity constraints imposed by near-term quantum hardware are satisfied. QMP is a pivotal task for quantum circuit compilation and its decision version is NP-complete. In this study, we present an effective approach called Adaptive Divided-And-Conqure (ADAC) to solve QMP. Our ADAC algorithm adaptively partitions circuits by leveraging subgraph isomorphism and ensuring coherence among subcircuits. Additionally, we employ a heuristic approach to optimise the routing algorithm during circuit partitioning. Through extensive experiments across various NISQ devices and circuit benchmarks, we demonstrate that the proposed ADAC algorithm outperforms the state-of-the-art method. Specifically, ADAC shows an improvement of nearly 50\% on the IBM Tokyo architecture. Furthermore, ADAC exhibits an improvement of around 18\% on pseudo-realistic circuits implemented on grid-like architectures with larger qubit numbers, where the pseudo-realistic circuits are constructed based on the characteristics of widely existing realistic circuits, aiming to investigate the applicability of ADAC. Our findings highlight the potential of ADAC in quantum circuit compilation and the deployment of practical applications on near-term quantum hardware platforms. △ Less

Submitted 7 September, 2024; originally announced September 2024.

Conditional Diffusion-based Parameter Generation for Quantum Approximate Optimization Algorithm

Authors: Fanxu Meng, Xiangzhen Zhou, Pengcheng Zhu, Yu Luo

Abstract: The Quantum Approximate Optimization Algorithm (QAOA) is a hybrid quantum-classical algorithm that shows promise in efficiently solving the MaxCut problem, a representative example of combinatorial optimization. However, its effectiveness heavily depends on the parameter optimization pipeline, where the parameter initialization strategy is nontrivial due to the non-convex and complex optimization… ▽ More The Quantum Approximate Optimization Algorithm (QAOA) is a hybrid quantum-classical algorithm that shows promise in efficiently solving the MaxCut problem, a representative example of combinatorial optimization. However, its effectiveness heavily depends on the parameter optimization pipeline, where the parameter initialization strategy is nontrivial due to the non-convex and complex optimization landscapes characterized by issues with low-quality local minima. Recent inspiration comes from the diffusion of classical neural network parameters, which has demonstrated that neural network training can benefit from generating good initial parameters through diffusion models. Therefore, in this work, we formulate the problem of finding good initial parameters as a generative task and propose the initial parameter generation scheme through dataset-conditioned pre-trained parameter sampling. Concretely, the generative machine learning model, specifically the denoising diffusion probabilistic model (DDPM), is trained to learn the distribution of pretrained parameters conditioned on the graph dataset. Intuitively, our proposed framework aims at effectively distilling knowledge from pre-trained parameters to generate well-performing initial parameters for QAOA. Compared to random parameter initialization, experiments on various-sized Max-Cut problem instances consistently show that our conditional DDPM is capable of improving the approximation ratio by as much as 14.4%, 11.0%, 11.4% and 7.49%, 8.31%, 6.08% on average for random, regular, and Watts-Strogatz graphs, respectively. Additionally, the experimental results also indicate that the conditional DDPM trained on small problem instances can be extrapolated to larger ones, improving the approximation ratio by up to 28.4% and 12.1% on average. △ Less

Submitted 17 January, 2025; v1 submitted 16 July, 2024; originally announced July 2024.

MindSpore Quantum: A User-Friendly, High-Performance, and AI-Compatible Quantum Computing Framework

Authors: Xusheng Xu, Jiangyu Cui, Zidong Cui, Runhong He, Qingyu Li, Xiaowei Li, Yanling Lin, Jiale Liu, Wuxin Liu, Jiale Lu, Maolin Luo, Chufan Lyu, Shijie Pan, Mosharev Pavel, Runqiu Shu, Jialiang Tang, Ruoqian Xu, Shu Xu, Kang Yang, Fan Yu, Qingguo Zeng, Haiying Zhao, Qiang Zheng, Junyuan Zhou, Xu Zhou , et al. (14 additional authors not shown)

Abstract: We introduce MindSpore Quantum, a pioneering hybrid quantum-classical framework with a primary focus on the design and implementation of noisy intermediate-scale quantum (NISQ) algorithms. Leveraging the robust support of MindSpore, an advanced open-source deep learning training/inference framework, MindSpore Quantum exhibits exceptional efficiency in the design and training of variational quantum… ▽ More We introduce MindSpore Quantum, a pioneering hybrid quantum-classical framework with a primary focus on the design and implementation of noisy intermediate-scale quantum (NISQ) algorithms. Leveraging the robust support of MindSpore, an advanced open-source deep learning training/inference framework, MindSpore Quantum exhibits exceptional efficiency in the design and training of variational quantum algorithms on both CPU and GPU platforms, delivering remarkable performance. Furthermore, this framework places a strong emphasis on enhancing the operational efficiency of quantum algorithms when executed on real quantum hardware. This encompasses the development of algorithms for quantum circuit compilation and qubit mapping, crucial components for achieving optimal performance on quantum processors. In addition to the core framework, we introduce QuPack, a meticulously crafted quantum computing acceleration engine. QuPack significantly accelerates the simulation speed of MindSpore Quantum, particularly in variational quantum eigensolver (VQE), quantum approximate optimization algorithm (QAOA), and tensor network simulations, providing astonishing speed. This combination of cutting-edge technologies empowers researchers and practitioners to explore the frontiers of quantum computing with unprecedented efficiency and performance. △ Less

Submitted 10 July, 2024; v1 submitted 24 June, 2024; originally announced June 2024.

Realizing a spatially correlated lattice interferometer

Authors: Peng Peng, Dekai Mao, Yi Liang, Guoling Yin, Hongmian Shui, Bo Song, Xiaoji Zhou

Abstract: Atom interferometers provide a powerful tool for measuring physical constants and testifying fundamental physics with unprecedented precision. Conventional atom interferometry focuses on the phase difference between two paths and utilizes matter waves with fixed coherence. Here, we report on realizing a Ramsey-Bordé interferometer of coherent matter waves dressed by a moving optical lattice in the… ▽ More Atom interferometers provide a powerful tool for measuring physical constants and testifying fundamental physics with unprecedented precision. Conventional atom interferometry focuses on the phase difference between two paths and utilizes matter waves with fixed coherence. Here, we report on realizing a Ramsey-Bordé interferometer of coherent matter waves dressed by a moving optical lattice in the gravity direction, and explore the resulting interference along multiple paths with tunable coherence. We investigate spatial correlations of atoms both within the lattice and between two arms by interferometry, and observe the emerging multiple interference peaks owing to the long-range coherence nature of the Bose-Einstein condensate. Our findings agree well with theoretical simulations, paving the way for high-precision interferometry with ultracold atoms. △ Less

Submitted 24 June, 2024; originally announced June 2024.

Bell nonlocality and entanglement in $e^{+}e^{-} \rightarrow Y\bar{Y}$ at BESIII

Authors: Sihao Wu, Chen Qian, Qun Wang, Xiao-Rong Zhou

Abstract: The Bell nonlocality and entanglement are two kinds of quantum correlations in quantum systems. Due to the recent upgrade in Beijing Spectrometer III (BESIII) experiment, it is possible to explore the nonlocality and entanglement in hyperon-antihyperon systems produced in electron-positron annihilation with high precision data. We provide a systematic method for studying quantum correlations in sp… ▽ More The Bell nonlocality and entanglement are two kinds of quantum correlations in quantum systems. Due to the recent upgrade in Beijing Spectrometer III (BESIII) experiment, it is possible to explore the nonlocality and entanglement in hyperon-antihyperon systems produced in electron-positron annihilation with high precision data. We provide a systematic method for studying quantum correlations in spin-1/2 hyperon-antihyperon systems through the measures for the nonlocality and entanglement. We find that with nonvanishing polarizations of the hyperon and its antihyperon, the kinematic region of nonlocality in the hyperon-antihyperon system is more restricted than the $τ^{+}τ^{-}$ system in which polarizations of $τ$ leptons are vanishing. We also present an experimental proposal to probe the nonlocality and entanglement in hyperon-antihyperon systems at BSEIII. △ Less

Submitted 28 June, 2024; v1 submitted 23 June, 2024; originally announced June 2024.

Comments: 9 pages, 4 figures, 4 tables. We corrected a few errors in plotting figures from analytical formula. Some results in tables read from figures have also been corrected. A new table (Table III) was added for the maximum concurrence and their corresponding angles. A few references were added

Large-scale cluster quantum microcombs

Authors: Ze Wang, Kangkang Li, Yue Wang, Xin Zhou, Yinke Cheng, Boxuan Jing, Fengxiao Sun, Jincheng Li, Zhilin Li, Bingyan Wu, Qihuang Gong, Qiongyi He, Bei-Bei Li, Qi-Fan Yang

Abstract: An optical frequency comb comprises a cluster of equally spaced, phase-locked spectral lines. Replacing these classical components with correlated quantum light gives rise to cluster quantum frequency combs, providing abundant quantum resources for measurement-based quantum computation and multi-user quantum networks. We propose and generate cluster quantum microcombs within an on-chip optical mic… ▽ More An optical frequency comb comprises a cluster of equally spaced, phase-locked spectral lines. Replacing these classical components with correlated quantum light gives rise to cluster quantum frequency combs, providing abundant quantum resources for measurement-based quantum computation and multi-user quantum networks. We propose and generate cluster quantum microcombs within an on-chip optical microresonator driven by multi-frequency lasers. Through resonantly enhanced four-wave mixing processes, continuous-variable cluster states with 60 qumodes are deterministically created. The graph structures can be programmed into one- and two-dimensional lattices by adjusting the configurations of the pump lines, which are confirmed inseparable based on the measured covariance matrices. Our work demonstrates the largest-scale cluster states with unprecedented raw squeezing levels from a photonic chip, offering a compact and scalable platform for computational and communicational tasks with quantum advantages. △ Less

Submitted 16 December, 2024; v1 submitted 15 June, 2024; originally announced June 2024.

Atomic transport dynamics in crossed optical dipole trap

Authors: Peng Peng, Zhengxi Zhang, Yaoyuan Fan, Guoling Yin, Dekai Mao, Xuzong Chen, Wei Xiong, Xiaoji Zhou

Abstract: We study the dynamical evolution of cold atoms in crossed optical dipole trap theoretically and experimentally. The atomic transport process is accompanied by two competitive kinds of physical mechanics, atomic loading and atomic loss. The loading process normally is negligible in the evaporative cooling experiment on the ground, while it is significant in the preparation of ultra-cold atoms in th… ▽ More We study the dynamical evolution of cold atoms in crossed optical dipole trap theoretically and experimentally. The atomic transport process is accompanied by two competitive kinds of physical mechanics, atomic loading and atomic loss. The loading process normally is negligible in the evaporative cooling experiment on the ground, while it is significant in the preparation of ultra-cold atoms in the space station. Normally, the atomic loading process is much weaker than the atomic loss process, and the atomic number in the center region of the trap decreases monotonically, as reported in previous research. However, when the atomic loading process is comparable to the atomic loss process, the atomic number in the center region of the trap will initially increase to a maximum value and then slowly decrease, and we have observed the phenomenon first. The increase of atomic number in the center region of the trap shows the presence of the loading process, and this will be significant especially under microgravity conditions. We build a theoretical model to analyze the competitive relationship, which coincides with the experimental results well. Furthermore, we have also given the predicted evolutionary behaviors under different conditions. This research provides a solid foundation for further understanding of the atomic transport process in traps. The analysis of loading process is of significant importance for the preparation of ultra-cold atoms in a crossed optical dipole trap under microgravity conditions. △ Less

Submitted 15 May, 2024; originally announced May 2024.

Entanglement Distribution Delay Optimization in Quantum Networks with Distillation

Authors: Mahdi Chehimi, Kenneth Goodenough, Walid Saad, Don Towsley, Tony X. Zhou

Abstract: Quantum networks (QNs) distribute entangled states to enable distributed quantum computing and sensing applications. However, in such QNs, quantum switches (QSs) have limited resources that are highly sensitive to noise and losses and must be carefully allocated to minimize entanglement distribution delay. In this paper, a QS resource allocation framework is proposed, which jointly optimizes the a… ▽ More Quantum networks (QNs) distribute entangled states to enable distributed quantum computing and sensing applications. However, in such QNs, quantum switches (QSs) have limited resources that are highly sensitive to noise and losses and must be carefully allocated to minimize entanglement distribution delay. In this paper, a QS resource allocation framework is proposed, which jointly optimizes the average entanglement distribution delay and entanglement distillation operations, to enhance the end-to-end (e2e) fidelity and satisfy minimum rate and fidelity requirements. The proposed framework considers realistic QN noise and includes the derivation of the analytical expressions for the average quantum memory decoherence noise parameter, and the resulting e2e fidelity after distillation. Finally, practical QN deployment aspects are considered, where QSs can control 1) nitrogen-vacancy (NV) center SPS types based on their isotopic decomposition, and 2) nuclear spin regions based on their distance and coupling strength with the electron spin of NV centers. A simulated annealing metaheuristic algorithm is proposed to solve the QS resource allocation optimization problem. Simulation results show that the proposed framework manages to satisfy all users rate and fidelity requirements, unlike existing distillation-agnostic (DA), minimal distillation (MD), and physics-agnostic (PA) frameworks which do not perform distillation, perform minimal distillation, and does not control the physics-based NV center characteristics, respectively. Furthermore, the proposed framework results in around 30% and 50% reductions in the average e2e entanglement distribution delay compared to existing PA and MD frameworks, respectively. Moreover, the proposed framework results in around 5%, 7%, and 11% reductions in the average e2e fidelity compared to existing DA, PA, and MD frameworks, respectively. △ Less

Submitted 14 May, 2024; originally announced May 2024.

Comments: 13 pages, 6 figures

Distributed Exact Generalized Grover's Algorithm

Authors: Xu Zhou, Xusheng Xu, Shenggen Zheng, Le Luo

Abstract: Distributed quantum computation has garnered immense attention in the noisy intermediate-scale quantum (NISQ) era, where each computational node necessitates fewer qubits and quantum gates. In this paper, we focus on a generalized search problem involving multiple targets within an unordered database and propose a Distributed Exact Generalized Grover's Algorithm (DEGGA) to address this challenge b… ▽ More Distributed quantum computation has garnered immense attention in the noisy intermediate-scale quantum (NISQ) era, where each computational node necessitates fewer qubits and quantum gates. In this paper, we focus on a generalized search problem involving multiple targets within an unordered database and propose a Distributed Exact Generalized Grover's Algorithm (DEGGA) to address this challenge by decomposing it into arbitrary $t$ components, where $2 \leq t \leq n$. Specifically, (1) our algorithm ensures accuracy, with a theoretical probability of identifying the target states at $100\%$; (2) if the number of targets is fixed, the pivotal factor influencing the circuit depth of DEGGA is the partitioning strategy, rather than the magnitude of $n$; (3) our method requires a total of $n$ qubits, eliminating the need for auxiliary qubits; (4) we elucidate the resolutions (two-node and three-node) of a particular generalized search issue incorporating two goal strings (000000 and 111111) by applying DEGGA. The feasibility and effectiveness of our suggested approach is further demonstrated by executing the quantum circuits on MindSpore Quantum (a quantum simulation software). Eventually, through the decomposition of multi-qubit gates, DEGGA diminishes the utilization of quantum gates by $90.7\%$ and decreases the circuit depth by $91.3\%$ in comparison to the modified Grover's algorithm by Long. It is increasingly evident that distributed quantum algorithms offer augmented practicality. △ Less

Submitted 4 July, 2024; v1 submitted 11 May, 2024; originally announced May 2024.

Report number: 250239

Journal ref: Frontiers of Computer Science, 2025

Universal non-Hermitian flow in one-dimensional PT-symmetric quantum criticalities

Authors: Xin-Chi Zhou, Ke Wang

Abstract: The critical point of a topological phase transition is described by a conformal field theory (CFT), where the finite-size corrections to the ground state energy are uniquely related to its central charge. We study the finite-size scaling of the energy of non-Hermitian Su-Schrieffer-Heeger (SSH) model with parity and time-reversal symmetry ($\mathcal{PT}$) symmetry. We find that under open boundar… ▽ More The critical point of a topological phase transition is described by a conformal field theory (CFT), where the finite-size corrections to the ground state energy are uniquely related to its central charge. We study the finite-size scaling of the energy of non-Hermitian Su-Schrieffer-Heeger (SSH) model with parity and time-reversal symmetry ($\mathcal{PT}$) symmetry. We find that under open boundary condition (OBC), the energy scaling $E(L)\sim c/L$ reveals a negative central charge $c=-2$ at the non-Hermitian critical point, indicative of a non-unitary CFT. Furthermore, we discover a universal scaling function capturing the flow of a system from Dirac CFT with $c=1$ to a non-unitary CFT with $c=-2$. The scaling function demonstrates distinct behaviors at topologically non-trivial and trivial sides of critical points. Notably, within the realm of topological criticality, the scaling function exhibits an universal rise-dip-rise pattern, manifesting a characteristic singularity inherent in the non-Hermitian topological critical points. The analytic expression of the scaling function has been derived and is in good agreement with the numerical results. △ Less

Submitted 2 May, 2024; originally announced May 2024.

Comments: 18 pages, 4 figures

A manufacturable platform for photonic quantum computing

Authors: Koen Alexander, Andrea Bahgat, Avishai Benyamini, Dylan Black, Damien Bonneau, Stanley Burgos, Ben Burridge, Geoff Campbell, Gabriel Catalano, Alex Ceballos, Chia-Ming Chang, CJ Chung, Fariba Danesh, Tom Dauer, Michael Davis, Eric Dudley, Ping Er-Xuan, Josep Fargas, Alessandro Farsi, Colleen Fenrich, Jonathan Frazer, Masaya Fukami, Yogeeswaran Ganesan, Gary Gibson, Mercedes Gimeno-Segovia , et al. (70 additional authors not shown)

Abstract: Whilst holding great promise for low noise, ease of operation and networking, useful photonic quantum computing has been precluded by the need for beyond-state-of-the-art components, manufactured by the millions. Here we introduce a manufacturable platform for quantum computing with photons. We benchmark a set of monolithically-integrated silicon photonics-based modules to generate, manipulate, ne… ▽ More Whilst holding great promise for low noise, ease of operation and networking, useful photonic quantum computing has been precluded by the need for beyond-state-of-the-art components, manufactured by the millions. Here we introduce a manufacturable platform for quantum computing with photons. We benchmark a set of monolithically-integrated silicon photonics-based modules to generate, manipulate, network, and detect photonic qubits, demonstrating dual-rail photonic qubits with $99.98\% \pm 0.01\%$ state preparation and measurement fidelity, Hong-Ou-Mandel quantum interference between independent photon sources with $99.50\%\pm0.25\%$ visibility, two-qubit fusion with $99.22\%\pm0.12\%$ fidelity, and a chip-to-chip qubit interconnect with $99.72\%\pm0.04\%$ fidelity, not accounting for loss. In addition, we preview a selection of next generation technologies, demonstrating low-loss silicon nitride waveguides and components, fabrication-tolerant photon sources, high-efficiency photon-number-resolving detectors, low-loss chip-to-fiber coupling, and barium titanate electro-optic phase shifters. △ Less

Submitted 26 April, 2024; originally announced April 2024.

Comments: 8 pages, 5 figures

Quantum Many-body Scar Models in One Dimensional Spin Chains

Authors: Jia-Wei Wang, Xiang-Fa Zhou, Guang-Can Guo, Zheng-Wei Zhou

Abstract: The phenomenon of quantum many-body scars has received widespread attention both in theoretical and experimental physics in recent years due to its unique physical properties. In this paper, based on the $su(2)$ algebraic relations, we propose a general method for constructing scar models by combining simple modules.This allows us to investigate many-body scar phenomena in high-spin systems. We nu… ▽ More The phenomenon of quantum many-body scars has received widespread attention both in theoretical and experimental physics in recent years due to its unique physical properties. In this paper, based on the $su(2)$ algebraic relations, we propose a general method for constructing scar models by combining simple modules.This allows us to investigate many-body scar phenomena in high-spin systems. We numerically verify the thermalization and non-integrability of this model and demonstrate the dynamical properties of the scar states. We also provide a theoretical analysis of the properties of these scar states. For spin-$1$ case, we find that our 1D chain model reduces to the famous PXP model[C. J. Turner et al. Phys. Rev. B 98, 155134(2018)] under special parameter condition. In addition, due to the continuous tunability of the parameters, our model also enables us to investigate the transitions of QMBS from non-integrable to integrable system. △ Less

Submitted 7 March, 2024; originally announced March 2024.

Comments: 12 pages, 7 figures

Journal ref: Phys. Rev. B 109, 125102 (2024)