Showing 1–24 of 24 results for author: Xie, L

An on-chip programmable mechano-quantum transducer

Authors: Xinrui Zhang, Wei Liu, Duanyu Ma, Lin-Ke Xie, Nai-Jie Guo, Zhongtao Gou, Yifan Wang, Jianxin Xu, Xiaoguang Luo, Zhao Mu, Honglong Chang, Weizheng Yuan, Jian-Shun Tang, Chuan-Feng Li, Guangcan Guo, Tao Ye

Abstract: Solid-state spin defects encode local perturbations as measurable shifts in spin-transition frequencies, but mechanical actuation and quantum readout remain physically separated, resulting in a discrete measurement setup. Integrating these functions requires an on-site mechano-quantum interface that programs the lattice state of a defect host and quantitatively maps it onto the spin Hamiltonian. H… ▽ More Solid-state spin defects encode local perturbations as measurable shifts in spin-transition frequencies, but mechanical actuation and quantum readout remain physically separated, resulting in a discrete measurement setup. Integrating these functions requires an on-site mechano-quantum interface that programs the lattice state of a defect host and quantitatively maps it onto the spin Hamiltonian. Here we first report an on-chip programmable mechano-quantum transducer (OCPMQT) that integrates voltage-defined micromechanical actuation with in situ spin-frequency readout in a two-dimensional van der Waals quantum-defect host. Mechanically programmed lattice states are encoded as shifts in the axial zero-field splitting parameter and resolved by optically detected magnetic resonance (ODMR) spectroscopy. Within a chip volume of 2.05*10^-2 cm^3, the transducer accesses ODMR-inferred strains as low as 0.0080% and delivers a volumetric force density of approximately 2.6*10^4 N*m^-3. A micromechanical-to-spin-Hamiltonian framework links on-chip electromechanics, interfacial strain transfer, and strain-spin coupling, enabling the electrical control micromechanical input to be measured directly as spin-frequency response. △ Less

Submitted 26 July, 2026; v1 submitted 23 July, 2026; originally announced July 2026.

Optimal control with flag qubits

Authors: Liang-Xu Xie, Lui Zuccherelli de Paula, Weizhou Cai, Qing-Xuan Jie, Luyan Sun, Chang-Ling Zou, Guang-Can Guo, Zi-Jie Chen, Xu-Bo Zou

Abstract: High-fidelity quantum operations are the cornerstone of fault-tolerant quantum computation. In open quantum systems, traditional optimal control only passively resists decoherence, leaving environment-induced uncertainty as a fundamental performance bottleneck. To overcome this, we propose a new optimal control framework with flag ancillas and the Flag-GRAPE algorithm, which can actively tailor th… ▽ More High-fidelity quantum operations are the cornerstone of fault-tolerant quantum computation. In open quantum systems, traditional optimal control only passively resists decoherence, leaving environment-induced uncertainty as a fundamental performance bottleneck. To overcome this, we propose a new optimal control framework with flag ancillas and the Flag-GRAPE algorithm, which can actively tailor the system's noise structure. Through embedding post-selection directly into the objective function, Flag-GRAPE correlates decoherence errors with the ancilla's unexpected state. Subsequent measurement and post-selection effectively expel this uncertainty, circumventing the fidelity bounds of traditional control. Numerical simulations in a superconducting quantum circuit demonstrate a $51\%$ reduction in infidelity compared to traditional closed-system pulses and also show that such enhancement is robust across broad noise regimes. Furthermore, by actively converting unstructured decoherence into heralded erasure errors, Flag-GRAPE is inherently compatible with quantum error correction. We demonstrate this by initializing a logical cat-code state, showing that the combination between Flag-GRAPE and QEC yields immediate state preparation enhancements. This new framework can reduce hardware overhead for fault-tolerant architectures and open up a practical path toward logical state preparation gain in near-term experiments. △ Less

Submitted 12 March, 2026; originally announced March 2026.

Comments: 8 pages, 4 figures

Fault-tolerant preparation of arbitrary logical states in the cat code

Authors: Zi-Jie Chen, Weizhou Cai, Liang-Xu Xie, Qing-Xuan Jie, Xu-Bo Zou, Guang-Can Guo, Luyan Sun, Chang-Ling Zou

Abstract: Preparing high-fidelity logical states is a central challenge in fault-tolerant quantum computing, yet existing approaches struggle to balance control complexity against resource overhead. Here, we present a complete framework for the fault-tolerant preparation of arbitrary logical states encoded in the four-legged cat code. This framework is engineered to suppress the dominant incoherent errors,… ▽ More Preparing high-fidelity logical states is a central challenge in fault-tolerant quantum computing, yet existing approaches struggle to balance control complexity against resource overhead. Here, we present a complete framework for the fault-tolerant preparation of arbitrary logical states encoded in the four-legged cat code. This framework is engineered to suppress the dominant incoherent errors, including excitation decay and dephasing in both the bosonic mode and the ancilla via error detection. Numerical simulations with experimentally realistic parameters on a 3D superconducting cavity platform yield logical infidelities on the order of $10^{-4}$. A scaling analysis confirms that the logical error rate grows nearly quadratically with the physical error rate, confirming that all first-order errors are fully suppressed. Our protocol is compatible with current hardware and is scalable to multiple bosonic modes, providing a resource-efficient foundation for magic state preparation and higher-level concatenated quantum error correction. △ Less

Submitted 19 February, 2026; originally announced February 2026.

Comments: 6 pages, 4 figures

A hybrid-frequency on-chip programmable synthetic-dimension simulator with arbitrary couplings

Authors: Xiao-Dong Zeng, Zhao-An Wang, Jia-Ming Ren, Yi-Tao Wang, Chun Ao, Wei Liu, Nai-Jie Guo, Lin-Ke Xie, Jun-You Liu, Yu-Hang Ma, Ya-Qi Wu, Shuang Wang, Pei-Yun Li, Zong-Quan Zhou, Mu Yang, Jin-Shi Xu, Xi-Wang Luo, Jian-Shun Tang, Chuan-Feng Li, Guang-Can Guo

Abstract: High-performance photonic chips provide a powerful platform for analog computing, enabling the simulation of high-dimensional physical systems using low-dimensional devices with additional synthetic dimensions. The realization of large-scale complex simulations necessitates an architecture capable of arbitrary coupling configurations (encompassing symmetric, asymmetric and long-range coupling sche… ▽ More High-performance photonic chips provide a powerful platform for analog computing, enabling the simulation of high-dimensional physical systems using low-dimensional devices with additional synthetic dimensions. The realization of large-scale complex simulations necessitates an architecture capable of arbitrary coupling configurations (encompassing symmetric, asymmetric and long-range coupling schemes) which is also crucial for scaling up. Previous approaches rely on excessive physical components to introduce asymmetric coupling, however, are restricted in reconfiguring and scaling by the relatively complicated structures. Here, to solve this problem, we propose a hybrid-frequency synthetic-dimension simulator architecture that combines both intra-resonant and inter-resonant frequency-lattice sites, and experimentally demonstrate it using the thin-film lithium niobate (TFLN) photonic chip. Employing this hybrid programmable architecture, we are able to simulate both the regular and long-range coupled forms of diverse compound-lattice models, such as the Hall ladder, Creutz ladder (symmetric) and Su-Schrieffer-Heeger (SSH, asymmetric) model, on a single chip, simultaneously reducing the experimental requirements significantly. As results, the direct readout of the bandstructure of the SSH model is able to be achieved, to be distinguished from all previous works, and important phenomena such as spin-momentum locking, topological flat band and Aharonov-Bohm cage effect are also observed with lower experimental requirements. Furthermore, applications like piecewise-continuous optical frequency shifting can be enabled by cascading our devices. Our results offer promising insights for future large-scale complex on-chip simulators with arbitrary couplings. △ Less

Submitted 21 August, 2025; originally announced August 2025.

Comments: 11 pages, 4 figures

Temperature dependent single- and double-quantum relaxation of negatively charged boron vacancies in hexagonal boron nitride

Authors: Lin-Ke Xie, Wei Liu, Kaiyu Huang, Nai-Jie Guo, Jun-You Liu, Yu-Hang Ma, Ya-Qi Wu, Yi-Tao Wang, Zhao-an Wang, Xiao-Dong Zeng, Jia-Ming Ren, Chun Ao, Shuo Deng, Haifei Lu, Jian-Shun Tang, Chuan-Feng Li, Guang-Can Guo

Abstract: The negatively charged boron vacancy in two-dimensional hexagonal boron nitride has emerged as a promising candidate for quantum sensing. The coherence time of this defect spins which coherent quantum sensing resides in is limited spin-phonon interactions, while the underlying physical mechanism of the corresponding high-temperature behavior is still not fully understood. Here, we probe the single… ▽ More The negatively charged boron vacancy in two-dimensional hexagonal boron nitride has emerged as a promising candidate for quantum sensing. The coherence time of this defect spins which coherent quantum sensing resides in is limited spin-phonon interactions, while the underlying physical mechanism of the corresponding high-temperature behavior is still not fully understood. Here, we probe the single- and double-quantum relaxation rates on this center over the temperature range from 293 to 393 K. The results show that both relaxation rates increase with increasing temperature, and the double-quantum relaxation rate significantly increases rapidly. At high temperature (above 400 K), the double-quantum relaxation rate is much greater than single-quantum relaxation rate, and may dominate the decoherence channel of spin-phonon interactions. Using a theoretical model of second-order spin-phonon interactions, we attribute the high-temperature spin relaxation rates to interactions with higher-energy effective phonon mode, aiding the further understanding and guiding high-temperature sensing applications. △ Less

Submitted 17 June, 2025; originally announced June 2025.

Versatile photonic frequency synthetic dimensions using a single Mach-Zehnder-interferometer-assisted device on thin-film lithium niobate

Authors: Zhao-An Wang, Xiao-Dong Zeng, Yi-Tao Wang, Jia-Ming Ren, Chun Ao, Zhi-Peng Li, Wei Liu, Nai-Jie Guo, Lin-Ke Xie, Jun-You Liu, Yu-Hang Ma, Ya-Qi Wu, Shuang Wang, Jian-Shun Tang, Chuan-Feng Li, Guang-Can Guo

Abstract: Investigating physical models with photonic synthetic dimensions has been generating great interest in vast fields of science. The rapid developing thin-film lithium niobate (TFLN) platform, for its numerous advantages including high electro-optic coefficient and scalability, is well compatible with the realization of synthetic dimensions in the frequency together with spatial domain. While coupli… ▽ More Investigating physical models with photonic synthetic dimensions has been generating great interest in vast fields of science. The rapid developing thin-film lithium niobate (TFLN) platform, for its numerous advantages including high electro-optic coefficient and scalability, is well compatible with the realization of synthetic dimensions in the frequency together with spatial domain. While coupling resonators with fixed beam splitters is a common experimental approach, it often lacks tunability and limits coupling between adjacent lattices to sites occupying the same frequency domain positions. Here, on the contrary, we conceive the resonator arrays connected by electro-optic tunable Mach-Zehnder interferometers in our configuration instead of fixed beam splitters. By applying bias voltage and RF modulation on the interferometers, our design extends such coupling to long-range scenario and allows for continuous tuning on each coupling strength and synthetic effective magnetic flux. Therefore, our design enriches controllable coupling types that are essential for building programmable lattice networks and significantly increases versatility. As the example, we experimentally fabricate a two-resonator prototype on the TFLN platform, and on this single chip we realize well-known models including tight-binding lattices, topological Hall ladder and Creutz ladder. We directly observe the band structures in the quasi-momentum space and important phenomena such as spin-momentum locking and the Aharonov-Bohm cage effect. These results demonstrate the potential for convenient simulations of more complex models in our configuration. △ Less

Submitted 19 August, 2025; v1 submitted 20 November, 2024; originally announced November 2024.

Experimental observation of spin defects in van der Waals material GeS$_2$

Authors: W. Liu, S. Li, N. -J. Guo, X. -D. Zeng, L. -K. Xie, J. -Y. Liu, Y. -H. Ma, Y. -Q. Wu, Y. -T. Wang, Z. -A. Wang, J. -M. Ren, C. Ao, J. -S. Xu, J. -S. Tang, A. Gali, C. -F. Li, G. -C. Guo

Abstract: Spin defects in atomically thin two-dimensional (2D) materials such as hexagonal boron nitride (hBN) attract significant attention for their potential quantum applications. The layered host materials not only facilitate seamless integration with optoelectronic devices but also enable the formation of heterostructures with on-demand functionality. Furthermore, their atomic thickness renders them pa… ▽ More Spin defects in atomically thin two-dimensional (2D) materials such as hexagonal boron nitride (hBN) attract significant attention for their potential quantum applications. The layered host materials not only facilitate seamless integration with optoelectronic devices but also enable the formation of heterostructures with on-demand functionality. Furthermore, their atomic thickness renders them particularly suitable for sensing applications. However, the short coherence times of the spin defects in hBN limit them in quantum applications that require extended coherence time. One primary reason is that both boron and nitrogen atoms have non-zero nuclear spins. Here, we present another 2D material germanium disulfide ($β$-GeS$_2$) characterized by a wide bandgap and potential nuclear-spin-free lattice. This makes it as a promising host material for spin defects that possess long-coherence time. Our findings reveal the presence of more than two distinct types of spin defects in single-crystal $β$-GeS$_2$. Coherent control of one type defect has been successfully demonstrated at both 5 K and room temperature, and the coherence time $T_2$ can achieve tens of microseconds, 100-folds of that of negatively charged boron vacancy (V$_{\text{B}}^-$) in hBN, satisfying the minimal threshold required for metropolitan quantum networks--one of the important applications of spins. We entatively assign the observed optical signals come from substitution defects. Together with previous theoretical prediction, we believe the coherence time can be further improved with optimized lattice quality, indicating $β$-GeS$_2$ as a promising host material for long-coherence-time spins. △ Less

Submitted 24 October, 2024; originally announced October 2024.

Comments: 8 pages, 5 figures

Experimental investigation of direct non-Hermitian measurement and uncertainty relation towards high-dimensional quantum domain

Authors: Yi-Tao Wang, Zhao-An Wang, Zhi-Peng Li, Xiao-Dong Zeng, Jia-Ming Ren, Wei Liu, Yuan-Ze Yang, Nai-Jie Guo, Lin-Ke Xie, Jun-You Liu, Yu-Hang Ma, Jian-Shun Tang, Chengjie Zhang, Chuan-Feng Li, Guang-Can Guo

Abstract: Non-Hermitian dynamics in quantum systems have unveiled novel phenomena, yet the implementation of valid non-Hermitian quantum measurement remains a challenge, because a universal quantum projective mechanism on the complete but skewed non-Hermitian eigenstates is not explicit in experiment. This limitation hinders the direct acquisition of non-Hermitian observable statistics (e.g., non-Hermitian… ▽ More Non-Hermitian dynamics in quantum systems have unveiled novel phenomena, yet the implementation of valid non-Hermitian quantum measurement remains a challenge, because a universal quantum projective mechanism on the complete but skewed non-Hermitian eigenstates is not explicit in experiment. This limitation hinders the direct acquisition of non-Hermitian observable statistics (e.g., non-Hermitian population dynamics), also constrains investigations of non-Hermitian quantum measurement properties such as uncertainty relation. Here, we address these challenges by presenting a non-Hermitian projective protocol and investigating the non-Hermitian uncertainty relation. We derive the uncertainty relation for pseudo-Hermitian (PH) observables that is generalized beyond the Hermitian ones. We then investigate the projective properties of general quantum states onto complete non-Hermitian eigenvectors, and present a quantum simulating method to apply the valid non-Hermitian projective measurement on a direct-sum dilated space. Subsequently, we experimentally construct a quantum simulator in the quantum optical circuit and realize the 3-dimensional non-Hermitian quantum measurement on the single-photon qutrit. Employing this platform, we explore the uncertainty relation experimentally with different PH metrics. Our non-Hermitian quantum measurement method is state-independent and outputs directly the non-Hermitian quantum projective statistics, paving the way for studies of extensive non-Hermitian observable in quantum domain. △ Less

Submitted 7 July, 2024; originally announced July 2024.

Comments: 6 pages, 4 figures

Quantum teleportation between a continuous-variable optical qumode and a discrete-variable solid-state qubit

Authors: Di Wang, Lei Xie, Jinfeng Liu, Yiling Song, Wei Xiong, Mingfeng Wang

Abstract: Quantum teleportation is a fundamental ingredient for quantum information science and technology. In particular, the ability to perform quantum teleportation between quantum systems of different natures and encoding types is crucial for building complex systems, such as distributed quantum internet. Here we propose a scheme to teleport a continuous variable optical qubit, encoded in an optical qum… ▽ More Quantum teleportation is a fundamental ingredient for quantum information science and technology. In particular, the ability to perform quantum teleportation between quantum systems of different natures and encoding types is crucial for building complex systems, such as distributed quantum internet. Here we propose a scheme to teleport a continuous variable optical qubit, encoded in an optical qumode by means of a superposed coherent state, onto a discrete variable solid-state qubit, associated with a single nitrogen-vacancy center spin in diamond, via a hybrid entanglement. By using a newly developed method for Bell-state measurement, which relies only on light homodyne detection and spin polarization measurement, near-deterministic and -perfect quantum teleportation can be achieved for large coherent-state amplitude input. Taking noise effects into account, we find that the average teleportation fidelity can still exceed the classical limit, enabling substantial teleportation distances under realistic experimental conditions. △ Less

Submitted 27 June, 2024; originally announced June 2024.

Edge State, Band Topology, and Time Boundary Effect in the Fine-Grained Categorization of Chern Insulators

Authors: H. C. Wu, H. S. Xu, L. C. Xie, L. Jin

Abstract: We predict novel topological phases with broken time-reversal symmetry supporting the coexistence of opposite chiral edge states, which are fundamentally different from the photonic spin-Hall, valley-Hall, and higher-order topological phases. We find a fine-grained categorization of Chern insulators, their band topologies characterized by identical Chern number are completely different. Furthermor… ▽ More We predict novel topological phases with broken time-reversal symmetry supporting the coexistence of opposite chiral edge states, which are fundamentally different from the photonic spin-Hall, valley-Hall, and higher-order topological phases. We find a fine-grained categorization of Chern insulators, their band topologies characterized by identical Chern number are completely different. Furthermore, we prove that different topologies cause zeros in their Bloch wavefunction overlaps, which imprint the band gap closing and appear at the degenerate points of topological phase transition. The Bloch wavefunction overlaps predict the reflection and refraction at a topological time boundary, and the overlap zeros ensure the existence of vanishing revival amplitude at critical times even though different topologies before and after the time boundary have identical Chern number. Our findings create new opportunities for topological metamaterials, uncover the topological feature hidden in the time boundary effect as a probe of topology, and open a venue for the exploration of the rich physics originating from the long-range couplings. △ Less

Submitted 2 February, 2024; originally announced February 2024.

Comments: 8 pages, 5 figures

Journal ref: Phys. Rev. Lett. 132, 083801 (2024)

Unitary and efficient spin squeezing in cavity optomechanics

Authors: Lei Xie, Zhiqi Yan, Lingxia Wang, Di Wang, Jinfeng Liu, Yiling Song, Wei Xiong, Mingfeng Wang

Abstract: We propose an approach to produce spin squeezed states of a large number of nitrogen-vacancy centers in diamond nanostructures coupled to an optical cavity. Unlike the previous squeezing method proposed by Bennett et al. [Phys. Rev. Lett. 110, 156402 (2013)], which is limited by phonon number fluctuations due to the existence of phonon-spin entanglement, our proposal can completely erase the entan… ▽ More We propose an approach to produce spin squeezed states of a large number of nitrogen-vacancy centers in diamond nanostructures coupled to an optical cavity. Unlike the previous squeezing method proposed by Bennett et al. [Phys. Rev. Lett. 110, 156402 (2013)], which is limited by phonon number fluctuations due to the existence of phonon-spin entanglement, our proposal can completely erase the entanglement between spins and hybrid phonon-photon mode mediating the effective spin-spin interaction, and thus achieves unitary one-axis-twisting interactions between nitrogen-vacancy centres, yielding a squeezing scaling $J^{-2/3}$, where J is the total angular momentum. We found that, under certain conditions, our method has the potential to enhance the spin-spin nonlinear interactions. We also proposed a scheme utilizing repeatedly applying the one-axis-twisting evolution to two orthogonal spin directions, which enables the transformation of the one-axis-twisting interactions into two-axis-twisting type, and therefore leads to the spin squeezing with Heisenberg-limited scaling $J^{-1}$. Taking into account the noise effects of spin dephasing and relaxtion, we found that the proposed approaches are robust against imperfections. △ Less

Submitted 27 January, 2024; originally announced January 2024.

Entangling spins using cubic nonlinear dynamics

Authors: Lingxia Wang, Yani Wang, Yujing Cheng, Zhiqi Yan, Lei Xie, Gang Liu, Jinmin Fan, Di Wang, Yiling Song, Linli He, Wei Xiong, Mingfeng Wang

Abstract: Entangled states with a large number of $N$ atomic spins are a key ingredient for quantum information processing and quantum metrology. Nowadays, the preparation of such states has mainly relied on the quadratic nonlinear dynamics. Here, we investigate the preparation of spin-spin multipartite entanglement, witnessed by quantum Fisher information, by using the cubic nonlinear dynamics. We find tha… ▽ More Entangled states with a large number of $N$ atomic spins are a key ingredient for quantum information processing and quantum metrology. Nowadays, the preparation of such states has mainly relied on the quadratic nonlinear dynamics. Here, we investigate the preparation of spin-spin multipartite entanglement, witnessed by quantum Fisher information, by using the cubic nonlinear dynamics. We find that, in the regime of weak coupling, the cubic scheme can greatly speed up the rate of entanglement generation as compared to the quadratic scheme (about $N$ times faster). In the strong coupling regime, the cubic nonlinear dynamics enables the periodic in time generation of a broad variety of new-type macroscopic superposition states, which allow us to realize near-Heisenberg-limit phase sensitivity. In addition, we also reveal an interesting feature that the amount of entanglement generated by the cubic scheme has a macroscopic sensitivity to the parity of $N$, which has no counterpart in quadratic nonlinear dynamics and can be exploited for sensing the parity of $N$ at the single-spin level. We also propose a new approach for a fast and high-fidelity generation of maximally entangled Greenberger-Horne-Zeilinger (GHZ) states. By using an alternative cubic-quadratic-admixture type of nonlinear interaction, we show that one may accelerate the procedure of GHZ-state generation. The realization of the cubic nonlinear dynamics is also considered, showing that the cubic nonlinear dynamics can be realized by either repeatedly using linear- and quadratic-nonlinear dynamics or utilizing light-mediated interactions in just one step. Finally, by taking realistic imperfections into account, we find that the cubic scheme is sensitivity to the single-spin decay in the strong coupling regime, while is robust against the collective dephasing. △ Less

Submitted 11 January, 2023; originally announced January 2023.

Report number: 18 pages, 7 figures, 1 table

Isotope effect on the Casimir force

Authors: Lanyi Xie, Fuwei Yang, Bai Song

Abstract: Isotopic dependence of the Casimir force is key to probing new physics and pushing novel technologies at the micro and nanoscale, but is largely unexplored. In 2002, an isotope effect of 10^(-4) was estimated for metals -- orders of magnitude beyond the experimental resolution. Here, by employing the Lifshitz theory, we reveal a significant isotope effect of over 10^(-1) for polar dielectrics. Thi… ▽ More Isotopic dependence of the Casimir force is key to probing new physics and pushing novel technologies at the micro and nanoscale, but is largely unexplored. In 2002, an isotope effect of 10^(-4) was estimated for metals -- orders of magnitude beyond the experimental resolution. Here, by employing the Lifshitz theory, we reveal a significant isotope effect of over 10^(-1) for polar dielectrics. This effect arises from the isotope-mass-induced line shift of the zone-center optical phonons and is insensitive to the linewidth. We perform numerical analyses on both the imaginary and real-frequency axes, and derive analytical formulas for predicting the isotope effect. △ Less

Submitted 5 September, 2022; originally announced September 2022.

Reflective Dielectric Cavity Enhanced Emission from Hexagonal Boron Nitride Spin Defect Arrays

Authors: Xiao-Dong Zeng, Yuan-Ze Yang, Nai-Jie Guo, Zhi-Peng Li, Zhao-An Wang, Lin-Ke Xie, Shang Yu, Yu Meng, Qiang Li, Jin-Shi Xu, Wei Liu, Yi-Tao Wang, Jian-Shun Tang, Chuan-Feng Li, Guang-Can Guo

Abstract: Among the various kinds of spin defects in hBN, the negatively charged boron vacancy ($\rm V_B^-$) spin defect that can be deterministically generated is undoubtedly a potential candidate for quantum sensing, but its low quantum efficiency restricts its %use in practical applications. Here, we demonstrate a robust enhancement structure with advantages including easy on-chip integration, convenient… ▽ More Among the various kinds of spin defects in hBN, the negatively charged boron vacancy ($\rm V_B^-$) spin defect that can be deterministically generated is undoubtedly a potential candidate for quantum sensing, but its low quantum efficiency restricts its %use in practical applications. Here, we demonstrate a robust enhancement structure with advantages including easy on-chip integration, convenient processing, low cost and suitable broad-spectrum enhancement for $\rm V_B^-$ defects. %Improved photoluminescence (PL) intensity and optically detected magnetic resonance (ODMR) contrast of $\rm V_B^-$ defect arrays. In the experiment, we used a metal reflective layer under the hBN flakes, filled with a transition dielectric layer in the middle, and adjusted the thickness of the dielectric layer to achieve the best coupling between the reflective dielectric cavity and the hBN spin defect. Using a reflective dielectric cavity, we achieved a PL enhancement of approximately 7-fold, and the corresponding ODMR contrast achieved 18\%. Additionally, the oxide layer of the reflective dielectric cavity can be used as an integrated material for micro-nano photonic devices for secondary processing, which means that it can be combined with other enhancement structures to achieve stronger enhancement. This work has guiding significance for realizing the on-chip integration of spin defects in two-dimensional materials. △ Less

Submitted 1 September, 2022; originally announced September 2022.

Suppressing ZZ Crosstalk of Quantum Computers through Pulse and Scheduling Co-Optimization

Authors: Lei Xie, Jidong Zhai, Zhenxing Zhang, Jonathan Allcock, Shengyu Zhang, Yi-Cong Zheng

Abstract: Noise is a significant obstacle to quantum computing, and $ZZ$ crosstalk is one of the most destructive types of noise affecting superconducting qubits. Previous approaches to suppressing $ZZ$ crosstalk have mainly relied on specific chip design that can complicate chip fabrication and aggravate decoherence. To some extent, special chip design can be avoided by relying on pulse optimization to sup… ▽ More Noise is a significant obstacle to quantum computing, and $ZZ$ crosstalk is one of the most destructive types of noise affecting superconducting qubits. Previous approaches to suppressing $ZZ$ crosstalk have mainly relied on specific chip design that can complicate chip fabrication and aggravate decoherence. To some extent, special chip design can be avoided by relying on pulse optimization to suppress $ZZ$ crosstalk. However, existing approaches are non-scalable, as their required time and memory grow exponentially with the number of qubits involved. To address the above problems, we propose a scalable approach by co-optimizing pulses and scheduling. We optimize pulses to offer an ability to suppress $ZZ$ crosstalk surrounding a gate, and then design scheduling strategies to exploit this ability and achieve suppression across the whole circuit. A main advantage of such co-optimization is that it does not require special hardware support. Besides, we implement our approach as a general framework that is compatible with different pulse optimization methods. We have conducted extensive evaluations by simulation and on a real quantum computer. Simulation results show that our proposal can improve the fidelity of quantum computing on $4{\sim}12$ qubits by up to $81\times$ ($11\times$ on average). Ramsey experiments on a real quantum computer also demonstrate that our method can eliminate the effect of $ZZ$ crosstalk to a great extent. △ Less

Submitted 15 February, 2022; originally announced February 2022.

Comments: 15 pages, 28 figures; comments are welcome

Journal ref: ASPLOS 2022: Proceedings of the 27th ACM International Conference on Architectural Support for Programming Languages and Operating Systems

Exploiting Different Levels of Parallelism in the Quantum Control Microarchitecture for Superconducting Qubits

Authors: Mengyu Zhang, Lei Xie, Zhenxing Zhang, Qiaonian Yu, Guanglei Xi, Huangliang Zhang, Fuming Liu, Yarui Zheng, Yicong Zheng, Shengyu Zhang

Abstract: As current Noisy Intermediate Scale Quantum (NISQ) devices suffer from decoherence errors, any delay in the instruction execution of quantum control microarchitecture can lead to the loss of quantum information and incorrect computation results. Hence, it is crucial for the control microarchitecture to issue quantum operations to the Quantum Processing Unit (QPU) in time. As in classical microarch… ▽ More As current Noisy Intermediate Scale Quantum (NISQ) devices suffer from decoherence errors, any delay in the instruction execution of quantum control microarchitecture can lead to the loss of quantum information and incorrect computation results. Hence, it is crucial for the control microarchitecture to issue quantum operations to the Quantum Processing Unit (QPU) in time. As in classical microarchitecture, parallelism in quantum programs needs to be exploited for speedup. However, three challenges emerge in the quantum scenario: 1) the quantum feedback control can introduce significant pipeline stall latency; 2) timing control is required for all quantum operations; 3) QPU requires a deterministic operation supply to prevent the accumulation of quantum errors. In this paper, we propose a novel control microarchitecture design to exploit Circuit Level Parallelism (CLP) and Quantum Operation Level Parallelism (QOLP). Firstly, we develop a Multiprocessor architecture to exploit CLP, which supports dynamic scheduling of different sub-circuits. This architecture can handle parallel feedback control and minimize the potential overhead that disrupts the timing control. Secondly, we propose a Quantum Superscalar approach that exploits QOLP by efficiently executing massive quantum instructions in parallel. Both methods issue quantum operations to QPU deterministically. In the benchmark test of a Shor syndrome measurement, a six-core implementation of our proposal achieves up to 2.59$\times$ speedup compared with a single core. For various canonical quantum computing algorithms, our superscalar approach achieves an average of 4.04$\times$ improvement over a baseline design. Finally, We perform a simultaneous randomized benchmarking (simRB) experiment on a real QPU using the proposed microarchitecture for validation. △ Less

Submitted 26 August, 2021; v1 submitted 19 August, 2021; originally announced August 2021.

Comments: Accepted to appear in the 54th IEEE/ACM International Symposium on Microarchitecture (MICRO-54) program

Cryptanalysis and improvement of a semi-quantum private comparison protocol based on Bell states

Authors: Li Xie, Qin Li, Fang Yu, Xiaoping Lou, Cai Zhang

Abstract: Semi-quantum private comparison (SQPC) allows two participants with limited quantum ability to securely compare the equality of their secrets with the help of a semi-dishonest third party (TP). Recently, Jiang proposed a SQPC protocol based on Bell states (Quantum Inf Process 19(6): 180, 2020) and claimed it is secure. In this paper, we present two types of attack on Jiang's SQPC protocol. In the… ▽ More Semi-quantum private comparison (SQPC) allows two participants with limited quantum ability to securely compare the equality of their secrets with the help of a semi-dishonest third party (TP). Recently, Jiang proposed a SQPC protocol based on Bell states (Quantum Inf Process 19(6): 180, 2020) and claimed it is secure. In this paper, we present two types of attack on Jiang's SQPC protocol. In the first type of attack, an outside eavesdropper will make participants accept a wrong result. In the second type of attack, a malicious participant will not only make the other participant accept a wrong result, but also learn the secret of the honest participant. Neither type of attack will be detected. In addition, we propose an improved SQPC protocol that can resist these two types of attack. △ Less

Submitted 5 January, 2021; v1 submitted 26 December, 2020; originally announced December 2020.

Comments: 10 pages and minor revisions are made

Pre- and post-selected measurements with coupling-strength-dependent modulation

Authors: Zhaoxue Li, Jiangdong Qiu, Xiaodong Qiu, Linguo Xie, Lan Luo, Xiong Liu, Yu He, Qi Wang, Zhiyou Zhang, JingLei Du

Abstract: Pre- and post-selected (PPS) measurement, especially the weak PPS measurement, is a useful protocol for amplifying small physical parameters. However, it is difficult to retain both the attainable highest measurement sensitivity and precision with the increase of the parameter to be measured. Here, a modulated PPS measurement scheme based on coupling-strength-dependent modulation is presented with… ▽ More Pre- and post-selected (PPS) measurement, especially the weak PPS measurement, is a useful protocol for amplifying small physical parameters. However, it is difficult to retain both the attainable highest measurement sensitivity and precision with the increase of the parameter to be measured. Here, a modulated PPS measurement scheme based on coupling-strength-dependent modulation is presented with the highest sensitivity and precision retained for an arbitrary coupling strength. This idea is demonstrated by comparing the modulated PPS measurement scheme with standard PPS measurementv scheme, respectively, in the cases of balanced pointer and unbalanced pointer. By using the Fisher information metric, we derive the optimal pre- and post-selected states, as well as the optimal coupling-strength-dependent modulation without any restriction on the coupling strength. We also give the specific strategy of performing the modulated PPS measurement scheme, which may promote practical application of this scheme in precision metrology. △ Less

Submitted 4 May, 2018; originally announced May 2018.

Enhancing the detection probability of single waveguided-photon by cavity technique

Authors: L. Y. Xie, L. F. Wei

Abstract: The resonant-cavity-enhanced (RCE) technique is an important approach to increasing the detection efficiency (DE) of typical free-space coupling photons. Here, we show that such a technique can also be utilized to increase the detection probability (DP) of a single waveguide-coupled photon. Based on a fully quantum mechanical theory in real space, we exactly calculated the absorption probability o… ▽ More The resonant-cavity-enhanced (RCE) technique is an important approach to increasing the detection efficiency (DE) of typical free-space coupling photons. Here, we show that such a technique can also be utilized to increase the detection probability (DP) of a single waveguide-coupled photon. Based on a fully quantum mechanical theory in real space, we exactly calculated the absorption probability of a single photon for a two-level detector next to the waveguide. We find that the DP of the waveguide photon for the detector in a waveguide-coupled ring cavity is significantly higher than that for the bare detector directly coupled to the photon. Physically, the DP of the photon for the bare detector next to the waveguide is always limited by the finite transmission and reflection probabilities of the photon. The cavity technique is used to store the photon and thus increase its DP. The feasibility of the proposal with current integrated optical devices is then discussed. △ Less

Submitted 16 March, 2016; originally announced March 2016.

Many-to-one remote information concentration for qudits and multipartite entanglement

Authors: Xin-Wen Wang, Shi-Qing Tang, Li-Jun Xie, Deng-Yu Zhang, Le-Man Kuang

Abstract: Telecloning and its reverse process, referred to as remote information concentration(RIC), have attracted considerable interest because of their potential applications in quantum-information processing. We here present a general scheme for RIC in d-level systems (qudits), in which the quantum information initially distributed in many spatially separated qudits can be remotely and deterministically… ▽ More Telecloning and its reverse process, referred to as remote information concentration(RIC), have attracted considerable interest because of their potential applications in quantum-information processing. We here present a general scheme for RIC in d-level systems (qudits), in which the quantum information initially distributed in many spatially separated qudits can be remotely and deterministically concentrated to a single qudit via an entangled channel without performing any global operations. We show that the entangled channel of RIC can be different types of entangled states, including mixed states as well as pure ones. More interestingly, these mixed states include a bound entangled state which has a similar form to the generalized Smolin state but has different characteristics from it. We also show that there exists a multipartite entangled state which can be used to implement both telecloning and RIC in the two-level system. Our many-to-one RIC protocol could be slightly modified to perform some types of many-to-many RIC tasks. △ Less

Submitted 21 July, 2013; v1 submitted 4 February, 2013; originally announced February 2013.

Comments: 11 pages, one figure

Journal ref: Quantum Information and Computation, 2014, 14: 0122-0136

Photonic two-qubit parity gate with tiny cross-Kerr nonlinearity

Authors: Xin-Wen Wang, Deng-Yu Zhang, Shi-Qing Tang, Li-Jun Xie, Zhi-Yong Wang, Le-Man Kuang

Abstract: The cross-Kerr nonlinearity (XKNL) effect can induce efficient photon interactions in principle with which photonic multiqubit gates can be performed using far fewer physical resources than linear optical schemes. Unfortunately, it is extremely challenging to generate giant cross-Kerr nonlinearities. In recent years, much effort has been made to perform multiqubit gates via weak XKNLs. However, th… ▽ More The cross-Kerr nonlinearity (XKNL) effect can induce efficient photon interactions in principle with which photonic multiqubit gates can be performed using far fewer physical resources than linear optical schemes. Unfortunately, it is extremely challenging to generate giant cross-Kerr nonlinearities. In recent years, much effort has been made to perform multiqubit gates via weak XKNLs. However, the required nonlinearity strengths are still difficult to achieve in the experiment. We here propose an XKNL-based scheme for realizing a two-photon polarization-parity gate, a universal two-qubit gate, in which the required strength of the nonlinearity could be orders of magnitude weaker than those required for previous schemes. The scheme utilizes a ring cavity fed by a coherent state as a quantum information bus which interacts with a path mode of the two polarized photons (qubits). The XKNL effect makes the bus pick up a phase shift dependent on the photon number of the path mode. Even when the potential phase shifts are very small they can be effectively measured using photon-number resolving detectors, which accounts for the fact that our scheme can work in the regime of tiny XKNL. The measurement outcome reveals the parity (even parity or odd parity) of the two polarization qubits. △ Less

Submitted 30 May, 2012; v1 submitted 28 December, 2011; originally announced December 2011.

Comments: 8 pages, 5 figures; some revisions have been made

Journal ref: Phys. Rev. A 85, 052326 (2012)

Remote information concentration and multipartite entanglement in multilevel systems

Authors: Xin-Wen Wang, Deng-Yu Zhang, Guo-Jian Yang, Shi-Qing Tang, Li-Jun Xie

Abstract: Remote information concentration (RIC) in $d$-level systems (qudits) is studied. It is shown that the quantum information initially distributed in three spatially separated qudits can be remotely and deterministically concentrated to a single qudit via an entangled channel without performing any global operations. The entangled channel can be different types of genuine multipartite pure entangled… ▽ More Remote information concentration (RIC) in $d$-level systems (qudits) is studied. It is shown that the quantum information initially distributed in three spatially separated qudits can be remotely and deterministically concentrated to a single qudit via an entangled channel without performing any global operations. The entangled channel can be different types of genuine multipartite pure entangled states which are inequivalent under local operations and classical communication. The entangled channel can also be a mixed entangled state, even a bound entangled state which has a similar form to the Smolin state, but has different features from the Smolin state. A common feature of all these pure and mixed entangled states is found, i.e., they have $d^2$ common commuting stabilizers. The differences of qudit-RIC and qubit-RIC ($d=2$) are also analyzed. △ Less

Submitted 9 October, 2011; v1 submitted 4 June, 2011; originally announced June 2011.

Comments: 10 pages, 3 figures

Journal ref: Phys. Rev. A 84, 042310 (2011)

Multiparty hierarchical quantum-information splitting

Authors: Xin-Wen Wang, Deng-Yu Zhang, Shi-Qing Tang, Li-Jun Xie

Abstract: We propose a scheme for multiparty hierarchical quantum-information splitting (QIS) with a multipartite entangled state, where a boss distributes a secret quantum state to two grades of agents asymmetrically. The agents who belong to different grades have different authorities for recovering boss's secret. Except for boss's Bell-state measurement, no nonlocal operation is involved. The presented s… ▽ More We propose a scheme for multiparty hierarchical quantum-information splitting (QIS) with a multipartite entangled state, where a boss distributes a secret quantum state to two grades of agents asymmetrically. The agents who belong to different grades have different authorities for recovering boss's secret. Except for boss's Bell-state measurement, no nonlocal operation is involved. The presented scheme is also shown to be secure against eavesdropping. Such a hierarchical QIS is expected to find useful applications in the field of modern multipartite quantum cryptography. △ Less

Submitted 19 January, 2011; originally announced January 2011.

Comments: 6 pages, 2 tables

Journal ref: J. Phys. B: At. Mol. Opt. Phys. 44 (2011) 035505

Generation of atomic entangled states in a bi-mode cavity via adiabatic passage

Authors: Li-Bo Chen, Peng Shi, Yong-Jian Gu, Lin Xie, Li-Zhen Ma

Abstract: We propose schemes to prepare atomic entangled states in a bi-mode cavity via stimulated Raman adiabatic passage (STIRAP) and fractional stimulated Raman adiabatic passage (f-STIRAP) tech- niques. According to the simulation results, our schemes keep the cavity modes almost unexcited and the atomic excited states are nearly unpopulated during the whole process. The simulation also shows that the… ▽ More We propose schemes to prepare atomic entangled states in a bi-mode cavity via stimulated Raman adiabatic passage (STIRAP) and fractional stimulated Raman adiabatic passage (f-STIRAP) tech- niques. According to the simulation results, our schemes keep the cavity modes almost unexcited and the atomic excited states are nearly unpopulated during the whole process. The simulation also shows that the error probability is very small. △ Less

Submitted 29 April, 2009; originally announced April 2009.

Comments: 6 pages, 3 figures

Journal ref: Optics Comm. 284, 5020-5023 (2011)