Showing 1–50 of 132 results for author: He, Q

Foundation Model for Unified Characterization of Optical Quantum States

Authors: Xiaoting Gao, Yan Zhu, Feng-Xiao Sun, Ya-Dong Wu, Qiongyi He

Abstract: Machine learning methods have been used to infer specific properties of limited families of optical quantum states, but a unified model that predicts a broad range of properties for practically relevant-especially multimode non-Gaussian-states without full tomography is still lacking. Here we introduce the first foundation model for the characterization of optical quantum states across a wide rang… ▽ More Machine learning methods have been used to infer specific properties of limited families of optical quantum states, but a unified model that predicts a broad range of properties for practically relevant-especially multimode non-Gaussian-states without full tomography is still lacking. Here we introduce the first foundation model for the characterization of optical quantum states across a wide range of complexity, defined by three key factors: non-Gaussianity, number of modes, and degree of squeezing. We show that a single model pretrained on low-complexity states can be directly applied to characterize states of higher complexity. With limited fine-tuning, the model adapts to downstream tasks such as predicting quantum fidelity and Wigner negativity over a broad class of experimentally relevant states, including strongly non-Gaussian Schrödinger cat states, multimode systems with up to ten modes, and highly squeezed states with squeezing levels up to 10.4dB. Our results establish a unified framework for characterizing optical quantum states from limited measurement data, enabling efficient certification of quantum states relevant to optical quantum information computation, communication and metrology. △ Less

Submitted 21 December, 2025; originally announced December 2025.

Metrological Sensitivity beyond Gaussian Limits with Cubic Phase States

Authors: Jiajie Guo, Shuheng Liu, Boxuan Jing, Qiongyi He, Manuel Gessner

Abstract: Cubic phase states provide the essential non-Gaussian resource for continuous-variable quantum computing. We show that they also offer significant potential for quantum metrology, surpassing the phase-sensing sensitivity of all Gaussian states at equal average photon number. Optimal sensitivity requires only moderate initial squeezing, and the non-Gaussian advantage remains robust against loss and… ▽ More Cubic phase states provide the essential non-Gaussian resource for continuous-variable quantum computing. We show that they also offer significant potential for quantum metrology, surpassing the phase-sensing sensitivity of all Gaussian states at equal average photon number. Optimal sensitivity requires only moderate initial squeezing, and the non-Gaussian advantage remains robust against loss and detection noise. We identify optimal measurement strategies and show that several experimentally relevant preparation schemes surpass Gaussian limits, in some cases reaching the sensitivity of cubic phase states. Our results establish cubic phase states as a promising resource for quantum-enhanced precision measurements beyond Gaussian limits. △ Less

Submitted 3 December, 2025; originally announced December 2025.

Comments: 21 pages, 8 figures

Non-commutativity as a Universal Characterization for Enhanced Quantum Metrology

Authors: Ningxin Kong, Haojie Wang, Mingsheng Tian, Yilun Xu, Geng Chen, Yu Xiang, Qiongyi He

Abstract: A central challenge in quantum metrology is to effectively harness quantum resources to surpass classical precision bounds. Although recent studies suggest that the indefinite causal order may enable sensitivities to attain the super-Heisenberg scaling, the physical origins of such enhancements remain elusive. Here, we introduce the nilpotency index $\mathcal{K}$, which quantifies the depth of non… ▽ More A central challenge in quantum metrology is to effectively harness quantum resources to surpass classical precision bounds. Although recent studies suggest that the indefinite causal order may enable sensitivities to attain the super-Heisenberg scaling, the physical origins of such enhancements remain elusive. Here, we introduce the nilpotency index $\mathcal{K}$, which quantifies the depth of non-commutativity between operators during the encoding process, can act as a fundamental parameter governing quantum-enhanced sensing. We show that a finite $\mathcal{K}$ yields an enhanced scaling of root-mean-square error as $N^{-(1+\mathcal{K})}$. Meanwhile, the requirement for indefinite causal order arises only when the nested commutators become constant. Remarkably, in the limit $\mathcal{K} \to \infty$, exponential precision scaling $N^{-1}e^{-N}$ is achievable. We propose experimentally feasible protocols implementing these mechanisms, providing a systematic pathway towards practical quantum-enhanced metrology. △ Less

Submitted 27 November, 2025; originally announced November 2025.

Comments: 6 pages, 3 figures

Low-Energy Free-Electron Nonclassical Lasing

Authors: Mai Zhang, Yu Wang, Chang-Ling Zou, Lei Ying, Qiongyi He, Guang-Can Guo, Chun-Hua Dong

Abstract: Harnessing a beam of slow free electrons in artificial photonic structures offers a powerful, tunable platform for generating nonclassical light without the need for heavy physical equipment. Here we present a theory of nonclassical lasing, demonstrating how incoherent electrons in photonic crystal cavities can coherently emit photons through collective dynamics. When photon emission rate exceeds… ▽ More Harnessing a beam of slow free electrons in artificial photonic structures offers a powerful, tunable platform for generating nonclassical light without the need for heavy physical equipment. Here we present a theory of nonclassical lasing, demonstrating how incoherent electrons in photonic crystal cavities can coherently emit photons through collective dynamics. When photon emission rate exceeds cavity losses, nonclassical lasing with sub-Poissonian photon statistics emerges, driven by multi-photon Rabi oscillations. At specific coupling strengths, quantum state trapping effect emerges, producing high-fidelity Fock states at room temperature (e.g. nearly 90%-fidelity of four photon Fock state). Notably, the frequency of the emitted photons can be readily tuned via the velocity of the injected electrons to match cavity modes. This approach supports photonic integration and offers a scalable, energy-efficient platform for room-temperature quantum light sources and advanced studies in quantum electrodynamics. △ Less

Submitted 13 November, 2025; originally announced November 2025.

Witnessing genuine multipartite entanglement in phase space with controlled Gaussian unitaries

Authors: Lin Htoo Zaw, Jiajie Guo, Qiongyi He, Shuheng Liu, Matteo Fadel

Abstract: Many existing genuine multipartite entanglement (GME) witnesses for continuous-variable (CV) quantum systems typically rely on quadrature measurements, which is challenging to implement in platforms where the CV degrees of freedom can be indirectly accessed only through qubit readouts. In this work, we propose methods to implement GME witnesses through phase-space measurements in state-of-the-art… ▽ More Many existing genuine multipartite entanglement (GME) witnesses for continuous-variable (CV) quantum systems typically rely on quadrature measurements, which is challenging to implement in platforms where the CV degrees of freedom can be indirectly accessed only through qubit readouts. In this work, we propose methods to implement GME witnesses through phase-space measurements in state-of-the-art experimental platforms, leveraging controlled Gaussian unitaries readily available in qubit-CV architectures. Based on two theoretical results showing that sufficient Wigner negativity can certify GME, we present five concrete implementation schemes using controlled parity, displacement, and beamsplitter operations. Our witnesses can detect paradigmatic GME states like the Dicke and multipartite $N00N$ states, which include the W states as a special case, and GHZ-type entangled cat states. We analyze the performance of these witnesses under realistic noise conditions and finite measurement resolution, showing their robustness to experimental imperfections. Crucially, our implementations require exponentially fewer measurement settings than full tomography, with one scheme requiring only a single measurement on auxiliary modes. The methods are readily applicable to circuit/cavity quantum electrodynamics, circuit quantum acoustodynamics, as well as trapped ions and atoms systems, where such dichotomic phase-space measurements are already routinely performed as native readouts. △ Less

Submitted 30 October, 2025; originally announced October 2025.

"Enough" Wigner negativity implies genuine multipartite entanglement

Authors: Lin Htoo Zaw, Jiajie Guo, Qiongyi He, Matteo Fadel, Shuheng Liu

Abstract: Wigner negativity and genuine multipartite entanglement (GME) are key nonclassical resources that enable computational advantages and broader quantum-information tasks. In this work, we prove two theorems for multimode continuous-variable systems that relate these nonclassical resources. Both theorems show that "enough" Wigner negativity -- either a large-enough Wigner negativity volume along a su… ▽ More Wigner negativity and genuine multipartite entanglement (GME) are key nonclassical resources that enable computational advantages and broader quantum-information tasks. In this work, we prove two theorems for multimode continuous-variable systems that relate these nonclassical resources. Both theorems show that "enough" Wigner negativity -- either a large-enough Wigner negativity volume along a suitably-chosen two-dimensional slice, or a large-enough nonclassicality depth of the centre-of-mass of a system -- certifies the presence of GME. Moreover, violations of the latter inequality provide lower bounds of the trace distance to the set of non-GME states. Our results also provide sufficient conditions for generating GME by interfering a state with the vacuum through a multiport interferometer, complementing long-known necessary conditions. Beyond these fundamental connections, our methods have practical advantages for systems with native phase-space measurements: they require only measuring the Wigner function over a finite region, or measuring a finite number of characteristic function points. Such measurements are frequently performed with readouts common in circuit/cavity quantum electrodynamic systems, trapped ions and atoms, and circuit quantum acoustodynamic systems. As such, our GME criteria are readily implementable in these platforms. △ Less

Submitted 30 October, 2025; originally announced October 2025.

Detection of non-Gaussian quantum correlations through measurement-after-interaction protocols

Authors: Jiajie Guo, Feng-Xiao Sun, Matteo Fadel, Qiongyi He

Abstract: Additional state evolutions performed before measurement, also called measurement-after-interactions (MAI) protocols, have shown a great potential for increasing the sensitivity of metrological scenarios. Here, we go beyond this result and show that MAI techniques can significantly enhance the detection capability of witnesses for quantum correlations. In particular, we show the possibility of det… ▽ More Additional state evolutions performed before measurement, also called measurement-after-interactions (MAI) protocols, have shown a great potential for increasing the sensitivity of metrological scenarios. Here, we go beyond this result and show that MAI techniques can significantly enhance the detection capability of witnesses for quantum correlations. In particular, we show the possibility of detecting Einstein-Podolsky-Rosen steering and mode entanglement of non-Gaussian states from linear measurements only. Moreover, we show that such approach allows for a significantly higher noise robustness. △ Less

Submitted 30 October, 2025; originally announced October 2025.

Task-Oriented Gaussian Optimization for Non-Gaussian Resources in Continuous-Variable Quantum Computation

Authors: Boxuan Jing, Feng-Xiao Sun, Qiongyi He

Abstract: In continuous-variable systems, non-Gaussian resources are essential for achieving universal quantum computation that lies beyond classical simulation. Among the candidate states, the cubic phase state stands out as the simplest form of single-mode non-Gaussian resource, yet its experimental preparation still remains a great challenge. Although a variety of approximate schemes have been proposed t… ▽ More In continuous-variable systems, non-Gaussian resources are essential for achieving universal quantum computation that lies beyond classical simulation. Among the candidate states, the cubic phase state stands out as the simplest form of single-mode non-Gaussian resource, yet its experimental preparation still remains a great challenge. Although a variety of approximate schemes have been proposed to simulate the cubic phase state, they often fall short when deployed in concrete quantum tasks. In this work, we present a Gaussian optimization protocol that systematically refines the non-Gaussian resources, which significantly improves the performance of both magic-state-based and measurement-based quantum computation. Leveraging task-specific Gaussian operations on approximate cubic phase states, our protocol offers an experimentally feasible approach to enhance gate fidelity in magic-state-based quantum computation and reduce the variance of nonlinear quadrature measurement in measurement-based quantum computation. Building on this framework, we further propose a task-oriented non-Gaussian state preparation scheme based on superpositions in the Fock basis followed by squeezing and displacement. This strategy enables direct tailoring of resource states to specific task goals. Owing to its flexibility and generality, our framework provides a powerful and broadly applicable tool for enhancing performance across a wide range of continuous-variable quantum information protocols. △ Less

Submitted 19 September, 2025; originally announced September 2025.

Comments: 11 pages, 8 figures

Entanglement Dimensionality of Continuous Variable States From Phase-Space Quasi-Probabilities

Authors: Shuheng Liu, Jiajie Guo, Matteo Fadel, Qiongyi He, Marcus Huber, Giuseppe Vitagliano

Abstract: The dimensionality of entanglement is a core tenet of quantum information processing, especially quantum communication and computation. While it is natural to think of this dimensionality in finite dimensional systems, many of the implementations harnessing high Schmidt numbers are actually based on discretising the observables of continuous variable systems. For those instances, a core question i… ▽ More The dimensionality of entanglement is a core tenet of quantum information processing, especially quantum communication and computation. While it is natural to think of this dimensionality in finite dimensional systems, many of the implementations harnessing high Schmidt numbers are actually based on discretising the observables of continuous variable systems. For those instances, a core question is whether directly utilizing the toolbox of continuous variable quantum information processing leads to better and more robust characterisations of entanglement dimensionality in infinite dimensional systems. We affirmatively answer this question by introducing Schmidt number witnesses for CV systems, based directly on covariances of infinite dimensional Bloch operators that are readily accessible in experiments. We show that the direct estimation leads to increased robustness and versatility compared to first discretising the system and using canonical discrete variable techniques, which provides strong motivation for further developments of genuine CV methods for the characterization of entanglement dimensionality, as well as for their implementation in experiments. △ Less

Submitted 2 September, 2025; originally announced September 2025.

Comments: 15 pages, 5 figures

Would the fidelity of quantum teleportation be increased by a local filtering operation near a dilaton black hole under decoherence?

Authors: Chun-yao Liu, Zheng-wen Long, Qi-liang He

Abstract: Previous studies have shown that the effects of black holes and environmental decoherence generally negatively influence quantum correlations and the fidelity of quantum teleportation in curved spacetime. In our paper, we find that as the dilaton parameter increases, the fidelity of quantum teleportation can either decrease or increase, which suggests that even in the presence of system-environmen… ▽ More Previous studies have shown that the effects of black holes and environmental decoherence generally negatively influence quantum correlations and the fidelity of quantum teleportation in curved spacetime. In our paper, we find that as the dilaton parameter increases, the fidelity of quantum teleportation can either decrease or increase, which suggests that even in the presence of system-environment coupling, the dilaton effect of black hole can positive influence teleportation fidelity; specifically, the dilaton effect can create net fidelity in quantum teleportation under decoherence. This interesting result challenges the long-held belief that the effects of black holes and environmental decoherence can only reduce the fidelity of quantum teleportation. Additionally, we observe an unreported result: if the fidelity of quantum teleportation remains in the classical region, it can be transformed into the quantum region by utilizing a local filtering operation, thereby achieving better fidelity than classical communication. This impressive result may provide new insights for developing an experimental scheme to effectively implement quantum teleportation in the context of dilaton black holes under decoherence. △ Less

Submitted 31 August, 2025; originally announced September 2025.

Phase Coherent Transport in Two-Dimensional Tellurium Flakes

Authors: Mohammad Hafijur Rahaman, Nathan Sawyers, Mourad Benamara, Trudie Culverhouse, Repaka Maheswar, Qiyuan He, Hugh Churchill, Dharmraj Kotekar Patil

Abstract: Elemental tellurium (Te) is a compelling van der Waals material due to its interesting chiral crystal structure and predicted topological properties. Here, we report the fabrication and comprehensive quantum transport study of devices based on Te flakes with varying thicknesses. We demonstrate a hole mobility reaching up to 1000 cm2/V.s in a 17 nm thick flake at 30 Kelvin. At deep cryogenic temper… ▽ More Elemental tellurium (Te) is a compelling van der Waals material due to its interesting chiral crystal structure and predicted topological properties. Here, we report the fabrication and comprehensive quantum transport study of devices based on Te flakes with varying thicknesses. We demonstrate a hole mobility reaching up to 1000 cm2/V.s in a 17 nm thick flake at 30 Kelvin. At deep cryogenic temperatures (< 50mK), the transport characteristics transition from Coulomb blockade in the low carrier density regime to pronounced Fabry-Pérot (F-P) interference at higher densities. Notably, the visibility of these F-P oscillations is significantly enhanced in the thinner flake device. The application of a magnetic field reveals a clear Zeeman splitting of the conductance peaks. The rich variety of quantum transport phenomena observed underscores the high quality of our thin Te flakes and establishes them as a promising platform for exploring novel physics and device concepts, such as topological superconductivity and low-power spintronic applications. △ Less

Submitted 26 August, 2025; originally announced August 2025.

Comments: 25 pages, 4 figures, Supplementary 6 figures

Boundary-induced Phases in the Dissipative Dicke Lattice Model

Authors: Peng-Fei Wei, Yilun Xu, Fengxiao Sun, Qiongyi He, Peter Rabl, Zhihai Wang

Abstract: The superradiant phase transition in the dissipative Dicke lattice model, driven by on-site collective atom-photon interactions and inter-site photon hopping, is a cornerstone of nonequilibrium quantum many-body physics. However, little is still known about the influence of boundaries in experimental achievable systems of finite size. Here we investigate the dissipative superradiant phase transiti… ▽ More The superradiant phase transition in the dissipative Dicke lattice model, driven by on-site collective atom-photon interactions and inter-site photon hopping, is a cornerstone of nonequilibrium quantum many-body physics. However, little is still known about the influence of boundaries in experimental achievable systems of finite size. Here we investigate the dissipative superradiant phase transition in the Dicke lattice model with a small number of sites and reveal a striking sensitivity of this model to the nature of the boundary conditions. Specifically, we find that under open boundary conditions a whole zoo of superradiant phases with broken translational symmetry appears, which is not observed in the corresponding infinite lattice system. Our results demonstrate the crucial influence of boundary effects on the stationary phases of dissipative lattice models, which offers intriguing new opportunities for studying these phenomena in near term experimental realizations of such models in quantum optics and circuit QED. △ Less

Submitted 13 August, 2025; originally announced August 2025.

Comments: 7 Pages, 5 Figures

Observe novel tricritical phenomena in self-organized Fermi gas induced by higher order Fermi surface nesting

Authors: Yilun Xu, Feng-Xiao Sun, Qiongyi He

Abstract: Cold atom systems in optical lattices have long been recognized as an ideal platform for bridging condense matter physics and quantum optics. Here, we investigate the 1D fermionic superradiance in an optical lattice, and observe novel tricritical phenomena and multistability in finite-temperature cases. As a starting point, which can be analytically calculated, we compare the 1D and 2D Fermi gases… ▽ More Cold atom systems in optical lattices have long been recognized as an ideal platform for bridging condense matter physics and quantum optics. Here, we investigate the 1D fermionic superradiance in an optical lattice, and observe novel tricritical phenomena and multistability in finite-temperature cases. As a starting point, which can be analytically calculated, we compare the 1D and 2D Fermi gases in zero-temperature limit. It turns out that the tricritical point originates from the higher-order Fermi surface nesting (FSN), and the infrared divergence in 1D systems is absent in 2D cases. When extending to finite-temperature cases, our numerical results reveal that both quantum- and classical-type trcritical phenomena can be observed simultaneously. Moreover, there exists an optimal temperature for observing superradiance. This work provides a new approach to understanding the relation between quantum and classical phase transitions. △ Less

Submitted 7 August, 2025; originally announced August 2025.

Variational-toolbox-based separability detection of multiqubit states

Authors: Jin-Min Liang, Shao-Ming Fei, Qiongyi He

Abstract: Parametrized quantum circuits (PQCs) are crucial in variational quantum algorithms. While it is commonly believed that the optimal PQC is solely used to reproduce the target state, we here reveal that the optimal PQC can also provide valuable insights into the state's properties. We propose variational toolboxes to identify the $k$-separability of pure states, with or without preparation noise, by… ▽ More Parametrized quantum circuits (PQCs) are crucial in variational quantum algorithms. While it is commonly believed that the optimal PQC is solely used to reproduce the target state, we here reveal that the optimal PQC can also provide valuable insights into the state's properties. We propose variational toolboxes to identify the $k$-separability of pure states, with or without preparation noise, by checking the structure within the optimal PQCs. Additionally, we introduce adaptive optimization strategies to detect the $k$-separability of mixed states. Compared to fixed PQCs, our approach controls fewer parameters for low-rank states. Finally, we validate our methods through numerical demonstrations for various states. △ Less

Submitted 8 August, 2025; v1 submitted 5 June, 2025; originally announced June 2025.

Comments: v2: close to the published version

Journal ref: Phys. Rev. A 112, 022404 (2025)

Measurement-Incompatibility Constraints for Maximal Randomness

Authors: Tianqi Zheng, Yi Li, Yu Xiang, Qiongyi He

Abstract: Certifying maximal quantum randomness without assumptions about system dimension remains a pivotal challenge for secure communication and foundational studies. Here, we introduce a generalized framework to directly certify maximal randomness from observed probability distributions across systems with arbitrary user numbers, without relying on the Bell-inequality violations. By analyzing probabilit… ▽ More Certifying maximal quantum randomness without assumptions about system dimension remains a pivotal challenge for secure communication and foundational studies. Here, we introduce a generalized framework to directly certify maximal randomness from observed probability distributions across systems with arbitrary user numbers, without relying on the Bell-inequality violations. By analyzing probability distributions directly, we identify a class of quantum states and projective measurements that achieve maximal randomness in bipartite and tripartite scenarios, ensuring practical feasibility. Further analysis reveals a counterintuitive trade-off governing measurement incompatibility among users: sufficient incompatibility for one user permits arbitrarily small incompatibility for others, defying conventional symmetry assumptions in the Bell test. This asymmetry provides a pathway to optimize device-independent protocols by strategically distributing quantum resources. Our results establish a versatile and experimentally accessible route to scalable randomness certification, with implications for quantum cryptography and the physics of nonlocal correlations. △ Less

Submitted 13 July, 2025; v1 submitted 23 May, 2025; originally announced May 2025.

Comments: 6 pages, 4 figures, typos corrected, some statement modified

Distributed quantum sensing with measurement-after-interaction strategies

Authors: Jiajie Guo, Shuheng Liu, Matteo Fadel, Qiongyi He

Abstract: We investigate multiparameter quantum estimation protocols based on measurement-after-interaction (MAI) strategies, in which the probe state undergoes an additional evolution prior to linear measurements. As we show in our study, this extra evolution enables different level of advantages depending on whether it is implemented locally or nonlocally across the sensing nodes. By benchmarking MAI stra… ▽ More We investigate multiparameter quantum estimation protocols based on measurement-after-interaction (MAI) strategies, in which the probe state undergoes an additional evolution prior to linear measurements. As we show in our study, this extra evolution enables different level of advantages depending on whether it is implemented locally or nonlocally across the sensing nodes. By benchmarking MAI strategies in both discrete- and continuous-variable systems, we show that they can significantly enhance multiparameter sensitivity and robustness against detection noise, particularly when non-Gaussian probe states are employed, cases where standard linear measurements are often insufficient. We also derive analytical results for multiparameter squeezing and establish the corresponding scaling laws for spin-squeezed states, demonstrating that MAI protocols can reach the Heisenberg scaling. These results pave the way for immediate experimental implementation in platforms such as atomic ensembles and optical fields. △ Less

Submitted 8 May, 2025; originally announced May 2025.

Quantum Teleportation from Telecom Photons to Erbium-ion Ensembles

Authors: Yu-Yang An, Qian He, Wenyi Xue, Ming-Hao Jiang, Chengdong Yang, Yan-Qing Lu, Shining Zhu, Xiao-Song Ma

Abstract: To realize a quantum internet, the distribution of quantum states via quantum teleportation with quantum memories is a key ingredient. Being compatible with existing fiber networks, entangled photons and quantum memories at telecom-wavelength are of central interest for such a scalable quantum network. Here, we demonstrate quantum teleportation from a telecom-wavelength photonic qubit to a solid-s… ▽ More To realize a quantum internet, the distribution of quantum states via quantum teleportation with quantum memories is a key ingredient. Being compatible with existing fiber networks, entangled photons and quantum memories at telecom-wavelength are of central interest for such a scalable quantum network. Here, we demonstrate quantum teleportation from a telecom-wavelength photonic qubit to a solid-state quantum memory based on erbium-ion ensembles, which have a native optical transition at 1.5 $μ$m telecom C-band. To accomplish this, we use chip-scale silicon nitride micro-resonators to generate entangled photons with narrow linewidth, compatible with the quantum memory. We confirm the quality of the quantum teleportation procedure using quantum state and process tomography techniques, in which both the quantum state and process fidelities exceeds the classical limit. These results pave the way for the realization of scalable quantum networks based on solid-state devices. △ Less

Submitted 8 May, 2025; v1 submitted 8 May, 2025; originally announced May 2025.

Exceptional-Point-Induced Nonequilibrium Entanglement Dynamics in Bosonic Networks

Authors: Chenghe Yu, Mingsheng Tian, Ningxin Kong, Matteo Fadel, Xinyao Huang, Qiongyi He

Abstract: Exceptional points (EPs), arising in non-Hermitian systems, have garnered significant attention in recent years, enabling advancements in sensing, wave manipulation, and mode selectivity. However, their role in quantum systems, particularly in influencing quantum correlations, remains underexplored. In this work, we investigate how EPs control multimode entanglement in bosonic chains. Using a Bogo… ▽ More Exceptional points (EPs), arising in non-Hermitian systems, have garnered significant attention in recent years, enabling advancements in sensing, wave manipulation, and mode selectivity. However, their role in quantum systems, particularly in influencing quantum correlations, remains underexplored. In this work, we investigate how EPs control multimode entanglement in bosonic chains. Using a Bogoliubov-de Gennes (BdG) framework to describe the Heisenberg equations, we identify EPs of varying orders and uncover spectral transitions between purely real, purely imaginary, and mixed eigenvalue spectra. These spectral regions, divided by EPs, correspond to three distinct entanglement dynamics: oscillatory, exponential, and hybrid. Remarkably, we demonstrate that higher-order EPs, realized by non-integer-pi hopping phases or nonuniform interaction strengths, significantly enhance the degree of multimode entanglement compared to second-order EPs. Our findings provide a pathway to leveraging EPs for entanglement control and exhibit the potential of non-Hermitian physics in advancing quantum technologies. △ Less

Submitted 6 February, 2025; originally announced February 2025.

Comments: 7 pages, 4 figures

Quantifying entanglement dimensionality from the quantum Fisher information matrix

Authors: Shaowei Du, Shuheng Liu, Matteo Fadel, Giuseppe Vitagliano, Qiongyi He

Abstract: Entanglement is known to be an essential resource for a number of tasks, including quantum-enhanced metrology, and can thus be quantified by figures of merit related to those tasks. In quantum metrology this is emphasized by the connections between the quantum Fisher information (QFI), providing the ultimate bounds of precision, and multipartite entanglement quantifiers such as the depth of entang… ▽ More Entanglement is known to be an essential resource for a number of tasks, including quantum-enhanced metrology, and can thus be quantified by figures of merit related to those tasks. In quantum metrology this is emphasized by the connections between the quantum Fisher information (QFI), providing the ultimate bounds of precision, and multipartite entanglement quantifiers such as the depth of entanglement. In systems composed by many qudits, it is also important to characterize the dimensionality of entanglement across bipartitions, i.e., loosely speaking, the minimal number of levels that must be entangled with each other in a given bipartition. However, the impact of high-dimensional entanglement on the QFI remains unexplored. In this work, we fill this gap by deriving a quantum Fisher information matrix (QFIM) criterion for witnessing the entanglement dimensionality across bipartitions, along with scalar corollaries, which we also extend to the multipartite scenario. To further emphasize the significance of our results, we draw connections with the precision of multiparameter estimation, which also provides a practical way of implementing our methods in experiments. △ Less

Submitted 24 January, 2025; originally announced January 2025.

Comments: 12 pages, 1 figure

Detecting high-dimensional entanglement by local randomized projections

Authors: Jin-Min Liang, Shuheng Liu, Shao-Ming Fei, Qiongyi He

Abstract: The characterization of high-dimensional entanglement plays a crucial role in the field of quantum information science. Conventional methods perform either fixed measurement bases or randomized measurements with high-order moments. Here, we introduce a criterion for estimating the Schmidt number of bipartite high-dimensional states based on local randomized projections with first-order moments. To… ▽ More The characterization of high-dimensional entanglement plays a crucial role in the field of quantum information science. Conventional methods perform either fixed measurement bases or randomized measurements with high-order moments. Here, we introduce a criterion for estimating the Schmidt number of bipartite high-dimensional states based on local randomized projections with first-order moments. To extract more information from limited experimental data, we propose an estimation algorithm of the Schmidt number. We exhibit the performance of the proposed approach by considering the maximally entangled state under depolarizing and random noise models. Our approach not only obtains a more accurate estimation of the Schmidt number but also reduces the number of projections compared to known methods. △ Less

Submitted 2 January, 2025; originally announced January 2025.

Comments: 12 pages, 6 figures

Experimental certification of high-dimensional entanglement with randomized measurements

Authors: Ohad Lib, Shuheng Liu, Ronen Shekel, Qiongyi He, Marcus Huber, Yaron Bromberg, Giuseppe Vitagliano

Abstract: High-dimensional entangled states offer higher information capacity and stronger resilience to noise compared with two-dimensional systems. However, the large number of modes and sensitivity to random rotations complicate experimental entanglement certification. Here, we experimentally certify three-dimensional entanglement in a five-dimensional two-photon state using 800 Haar-random measurements… ▽ More High-dimensional entangled states offer higher information capacity and stronger resilience to noise compared with two-dimensional systems. However, the large number of modes and sensitivity to random rotations complicate experimental entanglement certification. Here, we experimentally certify three-dimensional entanglement in a five-dimensional two-photon state using 800 Haar-random measurements implemented via a 10-plane programmable light converter. We further demonstrate the robustness of this approach against random rotations, certifying high-dimensional entanglement despite arbitrary phase randomization of the optical modes. This method, which requires no common reference frame between parties, opens the door for high-dimensional entanglement distribution through long-range random links. △ Less

Submitted 5 December, 2024; originally announced December 2024.

Journal ref: Phys. Rev. Lett. 134, 210202 (2025)

The transfer of nonlocality between two- and three-qubit dissipative systems with counter-rotating-wave terms

Authors: Zi-Yu Xiong, Yong-Jun Xiao, Ye-Qi Zhang, Qi-Liang He

Abstract: We investigate the effect of counter-rotating-wave terms on nonlocality and entanglement for three qubits coupled with a common bath for strong and ultrastrong coupling regimes beyond the traditional treatment of Born-Markovian, perturbative and rotating wave approximations by employing the numerical hierarchical equations of motion approach. Our findings are as follows: (i) In the strong coupling… ▽ More We investigate the effect of counter-rotating-wave terms on nonlocality and entanglement for three qubits coupled with a common bath for strong and ultrastrong coupling regimes beyond the traditional treatment of Born-Markovian, perturbative and rotating wave approximations by employing the numerical hierarchical equations of motion approach. Our findings are as follows: (i) In the strong coupling regime, the counter-rotating terms accelerate the decay of genuine three-party correlations, and the obvious sudden birth of BN is found; (ii) In the ultrastrong coupling regime, we observe a novel phenomenon where nonlocality is consistently transferred between a three-qubit and its subsystem. Besides, the inclusion of counter-rotating wave terms obviously enhances genuine tripartite nonlocality; and (iii) These counter-rotating terms cannot effectively generate genuine three-party correlations in zero-excitation cases, which differs from previous studies involving only two qubits. △ Less

Submitted 12 December, 2024; v1 submitted 21 November, 2024; originally announced November 2024.

Comments: 10 pages, 7 figures

Report number: Phys. Rev. A 111, 042410

One-Sided Device-Independent Random Number Generation Through Fiber Channels

Authors: Jinfang Zhang, Yi Li, Mengyu Zhao, Dongmei Han, Jun Liu, Meihong Wang, Qihuang Gong, Yu Xiang, Qiongyi He, Xiaolong Su

Abstract: Randomness is an essential resource and plays important roles in various applications ranging from cryptography to simulation of complex systems. Certified randomness from quantum process is ensured to have the element of privacy but usually relies on the device's behavior. To certify randomness without the characterization for device, it is crucial to realize the one-sided device-independent rand… ▽ More Randomness is an essential resource and plays important roles in various applications ranging from cryptography to simulation of complex systems. Certified randomness from quantum process is ensured to have the element of privacy but usually relies on the device's behavior. To certify randomness without the characterization for device, it is crucial to realize the one-sided device-independent random number generation based on quantum steering, which guarantees security of randomness and relaxes the demands of one party's device. Here, we distribute quantum steering between two distant users through a 2 km fiber channel and generate quantum random numbers at the remote station with untrustworthy device. We certify the steering-based randomness by reconstructing covariance matrix of the Gaussian entangled state shared between distant parties. Then, the quantum random numbers with a generation rate of 7.06 Mbits/s are extracted from the measured amplitude quadrature fluctuation of the state owned by the remote party. Our results demonstrate the first realization of steering-based random numbers extraction in a practical fiber channel, which paves the way to the quantum random numbers generation in asymmetric networks. △ Less

Submitted 13 November, 2024; originally announced November 2024.

Real randomized measurements for analyzing properties of quantum states

Authors: Jin-Min Liang, Satoya Imai, Shuheng Liu, Shao-Ming Fei, Otfried Gühne, Qiongyi He

Abstract: Randomized measurements are useful for analyzing quantum systems especially when quantum control is not fully perfect. However, their practical realization typically requires multiple rotations in the complex space due to the adoption of random unitaries. Here, we introduce two simplified randomized measurements that limit rotations in a subspace of the complex space. The first is \textit{real ran… ▽ More Randomized measurements are useful for analyzing quantum systems especially when quantum control is not fully perfect. However, their practical realization typically requires multiple rotations in the complex space due to the adoption of random unitaries. Here, we introduce two simplified randomized measurements that limit rotations in a subspace of the complex space. The first is \textit{real randomized measurements} (RRMs) with orthogonal evolution and real local observables. The second is \textit{partial real randomized measurements} (PRRMs) with orthogonal evolution and imaginary local observables. We show that these measurement protocols exhibit different abilities in capturing correlations of bipartite systems. We explore various applications of RRMs and PRRMs in different quantum information tasks such as characterizing high-dimensional entanglement, quantum imaginarity, and predicting properties of quantum states with classical shadow. △ Less

Submitted 27 August, 2025; v1 submitted 8 November, 2024; originally announced November 2024.

Comments: 25 pages, 5 figures, v2: close to the published version

Journal ref: Phys. Rev. A 112, 022434 (2025)

Quantum entanglement in phase space

Authors: Shuheng Liu, Jiajie Guo, Qiongyi He, Matteo Fadel

Abstract: While commonly used entanglement criteria for continuous variable systems are based on quadrature measurements, here we study entanglement detection from measurements of the Wigner function. These are routinely performed in platforms such as trapped ions and circuit QED, where homodyne measurements are difficult to be implemented. We provide complementary criteria which we show to be tight for a v… ▽ More While commonly used entanglement criteria for continuous variable systems are based on quadrature measurements, here we study entanglement detection from measurements of the Wigner function. These are routinely performed in platforms such as trapped ions and circuit QED, where homodyne measurements are difficult to be implemented. We provide complementary criteria which we show to be tight for a variety of experimentally relevant Gaussian and non-Gaussian states. Our results show novel approaches to detect entanglement in continuous variable systems and shed light on interesting connections between known criteria and the Wigner function. △ Less

Submitted 31 August, 2025; v1 submitted 26 September, 2024; originally announced September 2024.

Comments: Comments are welcomed!

Necessary and Sufficient Condition for Randomness Certification from Incompatibility

Authors: Yi Li, Yu Xiang, Jordi Tura, Qiongyi He

Abstract: Quantum randomness can be certified from probabilistic behaviors demonstrating Bell nonlocality or Einstein-Podolsky-Rosen steering, leveraging outcomes from uncharacterized devices. However, such nonlocal correlations are not always sufficient for this task, necessitating the identification of required minimum quantum resources. In this work, we provide the necessary and sufficient condition for… ▽ More Quantum randomness can be certified from probabilistic behaviors demonstrating Bell nonlocality or Einstein-Podolsky-Rosen steering, leveraging outcomes from uncharacterized devices. However, such nonlocal correlations are not always sufficient for this task, necessitating the identification of required minimum quantum resources. In this work, we provide the necessary and sufficient condition for nonzero certifiable randomness in terms of measurement incompatibility and develop approaches to detect them. Firstly, we show that the steering-based randomness can be certified if and only if the correlations arise from a measurement compatibility structure that is not isomorphic to a hypergraph containing a star subgraph. In such a structure, the central measurement is individually compatible with the measurements at branch sites, precluding certifiable randomness in the central measurement outcomes. Subsequently, we generalize this result to the Bell scenario, proving that the violation of any chain inequality involving $m$ inputs and $d$ outputs rules out such a compatibility structure, thereby validating all chain inequalities as credible witnesses for randomness certification. Our results point out the role of incompatibility structure in generating random numbers, offering a way to identify minimum quantum resources for the task. △ Less

Submitted 23 September, 2024; originally announced September 2024.

Comments: 15 pages (incl. appendix), 3 figures

Journal ref: Phys. Rev. Lett. 135, 060201 (2025)

Classifying Multipartite Continuous Variable Entanglement Structures through Data-augmented Neural Networks

Authors: Xiaoting Gao, Mingsheng Tian, Feng-Xiao Sun, Ya-Dong Wu, Yu Xiang, Qiongyi He

Abstract: Neural networks have emerged as a promising paradigm for quantum information processing, yet they confront the challenge of generating training datasets with sufficient size and rich diversity, which is particularly acute when dealing with multipartite quantum systems. For instance, in the task of classifying different structures of multipartite entanglement in continuous variable systems, it is n… ▽ More Neural networks have emerged as a promising paradigm for quantum information processing, yet they confront the challenge of generating training datasets with sufficient size and rich diversity, which is particularly acute when dealing with multipartite quantum systems. For instance, in the task of classifying different structures of multipartite entanglement in continuous variable systems, it is necessary to simulate a large number of infinite-dimension state data that can cover as many types of non-Gaussian states as possible. Here, we develop a data-augmented neural network to complete this task with homodyne measurement data. A quantum data augmentation method based on classical data processing techniques and quantum physical principles is proposed to efficiently enhance the network performance. By testing on randomly generated tripartite and quadripartite states, we demonstrate that the network can indicate the entanglement structure among the various partitions and the accuracies are significantly improved with data augmentation. Our approach allows us to further extend the use of data-driven machine learning techniques to more complex tasks of learning quantum systems encoded in a large Hilbert space. △ Less

Submitted 29 October, 2024; v1 submitted 12 September, 2024; originally announced September 2024.

Graphical Framework for Non-Gaussian Quantum States

Authors: Lina Vandré, Boxuan Jing, Yu Xiang, Otfried Gühne, Qiongyi He

Abstract: We provide a graphical method to describe and analyze non-Gaussian quantum states using a hypergraph framework. These states are pivotal resources for quantum computing, communication, and metrology, but their characterization is hindered by their complex high-order correlations. The framework encapsulates transformation rules for a series of typical Gaussian unitary operation and local quadrature… ▽ More We provide a graphical method to describe and analyze non-Gaussian quantum states using a hypergraph framework. These states are pivotal resources for quantum computing, communication, and metrology, but their characterization is hindered by their complex high-order correlations. The framework encapsulates transformation rules for a series of typical Gaussian unitary operation and local quadrature measurement, offering a visually intuitive tool for manipulating such states through experimentally feasible pathways. Notably, we develop methods for the generation of complex hypergraph states with more or higher-order hyperedges from simple structures through Gaussian operations only, facilitated by our graphical rules. We present illustrative examples on the preparation of non-Gaussian states rooted in these graph-based formalisms, revealing their potential to advance continuous-variable general quantum computing capabilities. △ Less

Submitted 17 July, 2025; v1 submitted 11 September, 2024; originally announced September 2024.

Journal ref: Quantum 9, 1809 (2025)

Characterizing the Multipartite Entanglement Structure of Non-Gaussian Continuous-Variable States with a Single Evolution Operator

Authors: Mingsheng Tian, Xiaoting Gao, Boxuan Jing, Feng-Xiao Sun, Matteo Fadel, Manuel Gessner, Qiongyi He

Abstract: Multipartite entanglement is an essential resource for quantum information tasks, but characterizing entanglement structures in continuous variable systems remains challenging, especially in multimode non-Gaussian scenarios. In this work, we introduce an efficient method for detecting multipartite entanglement structures in continuous-variable states. Based on the quantum Fisher information, we pr… ▽ More Multipartite entanglement is an essential resource for quantum information tasks, but characterizing entanglement structures in continuous variable systems remains challenging, especially in multimode non-Gaussian scenarios. In this work, we introduce an efficient method for detecting multipartite entanglement structures in continuous-variable states. Based on the quantum Fisher information, we propose a systematic approach to identify an optimal encoding operator that can capture the quantum correlations in multimode non-Gaussian states. We demonstrate the effectiveness of our method on over $10^5$ randomly generated multimode-entangled quantum states, achieving a very high success rate in entanglement detection. Additionally, the robustness of our method can be considerably enhanced against losses by expanding the set of accessible operators. This work provides a general framework for characterizing entanglement structures in diverse continuous variable systems, enabling a number of experimentally relevant applications. △ Less

Submitted 24 September, 2025; v1 submitted 22 August, 2024; originally announced August 2024.

Journal ref: Phys. Rev. Lett. 135, 140201 (2025)

Randomness versus Nonlocality in Multi-input and Multi-output Quantum Scenario

Authors: Chao Zhang, Yi Li, Xiao-Min Hu, Yu Xiang, Chuan-Feng Li, Guang-Can Guo, Jordi Tura, Qihuang Gong, Qiongyi He, Bi-Heng Liu

Abstract: Device-independent randomness certification based on Bell nonlocality does not require any assumptions about the devices and therefore provides adequate security. Great effort has been made to demonstrate that nonlocality is necessary for generating quantum randomness, but the minimal resource required for random number generation has not been clarified. Here we first prove and experimentally demo… ▽ More Device-independent randomness certification based on Bell nonlocality does not require any assumptions about the devices and therefore provides adequate security. Great effort has been made to demonstrate that nonlocality is necessary for generating quantum randomness, but the minimal resource required for random number generation has not been clarified. Here we first prove and experimentally demonstrate that violating any two-input Bell inequality is both necessary and sufficient for certifying randomness, however, for the multi-input cases, this sufficiency ceases to apply, leading to certain states exhibiting Bell nonlocality without the capability to certify randomness. We examine two typical classes of Bell inequalities with multi-input and multi-output, the facet inequalities and Salavrakos-Augusiak-Tura-Wittek-Acín-Pironio Bell inequalities, in the high-dimensional photonic system, and observe the violation of the latter one can always certify randomness which is not true for the former. The private randomness with a generation rate of 1.867\pm0.018 bits per photon pair is obtained in the scenario of Salavrakos-Augusiak-Tura-Wittek-Acín-Pironio Bell inequalities with 3-input and 4-output. Our work unravels the internal connection between randomness and nonlocality, and effectively enhances the performance of tasks such as device-independent random number generation. △ Less

Submitted 5 September, 2024; v1 submitted 8 August, 2024; originally announced August 2024.

Comments: 25 pages, 6 figures

Journal ref: Physical Review Letters 134, 090201 (2025)

Using PT-symmetric Qubits to Break the Tradeoff Between Fidelity and the Degree of Quantum Entanglement

Authors: B. -B. Liu, Shi-Lei Su, Y. -L. Zuo, Qiongyi He, Gang Chen, F. Nori, H. Jing

Abstract: A noteworthy discovery is that the minimal evolution time is smaller for parity-time ($\mathcal{PT}$) symmetric systems compared to Hermitian setups. Moreover, there is a significant acceleration of two-qubit quantum entanglement preparation near the exceptional point (EP), or spectral coalescence, within such system. Nevertheless, an important problem often overlooked for quantum EP-based devices… ▽ More A noteworthy discovery is that the minimal evolution time is smaller for parity-time ($\mathcal{PT}$) symmetric systems compared to Hermitian setups. Moreover, there is a significant acceleration of two-qubit quantum entanglement preparation near the exceptional point (EP), or spectral coalescence, within such system. Nevertheless, an important problem often overlooked for quantum EP-based devices is their fidelity, greatly affected by the process of dissipation or post-selection, creating an inherent trade-off relation between the degree of entanglement and fidelity. Our study demonstrates that this limitation can be effectively overcome by harnessing an active $\mathcal{PT}$-symmetric system, which possesses balanced gain and loss, enabling maximal entanglement with rapid speed, high fidelity, and greater resilience to non-resonant errors. This new approach can efficiently prepare multi-qubit entanglement and use not only bipartite but also tripartite entanglement, as illustrative examples, even when the precise gain-loss balance is not strictly maintained. Our analytical findings are in excellent agreement with numerical simulations, confirming the potential of truly $\mathcal{PT}$-devices as a powerful tool for creating and engineering diverse quantum resources for applications in quantum information technology △ Less

Submitted 30 September, 2024; v1 submitted 11 July, 2024; originally announced July 2024.

Comments: 4 figures, 7 pages for main text. Totally 13 figures and 19 pages including appendix

Quantum phase transition in a quantum Rabi square with next-nearest-neighbor hopping

Authors: Yilun Xu, Feng-Xao Sun, Qiongyi He, Han Pu, Wei Zhang

Abstract: We propose a quantum Rabi square model where both the nearest-neighbor and the next-nearest-neighbor photon hopping are allowed among four quantum Rabi systems located at the vertices of a square. By tuning the next-nearest hopping strength, we realize a first-order phase transition between the antiferromagnetic superradiant phase and the frustrated superradiant phase, as well as a second-order ph… ▽ More We propose a quantum Rabi square model where both the nearest-neighbor and the next-nearest-neighbor photon hopping are allowed among four quantum Rabi systems located at the vertices of a square. By tuning the next-nearest hopping strength, we realize a first-order phase transition between the antiferromagnetic superradiant phase and the frustrated superradiant phase, as well as a second-order phase transition between the normal and the superradiant phases. To understand the emergence of such phases, we show analytically that the effect induced by next-nearest hopping is equivalent to that of an artificial gauge phase. Our findings suggest that the next-nearest-neighbor hopping can serve as an alternative for the gauge phase to realize quantum control in applications of quantum simulation and quantum materials, and that our model represents a basic building block for the frustrated $J_1$-$J_2$ quantum spin model on square lattices. △ Less

Submitted 3 July, 2024; originally announced July 2024.

Breeding the Cat Through Superposition of Two Schrodinger Kittens Based on Coupled Waveguides

Authors: Nuo Wang, Xinchen Zhang, Qi Liu, Fengxiao Sun, Qiongyi He, Ying Gu

Abstract: Optical Schrodinger's cat (SC) is highly anticipated because of the potential of realizing fault-tolerant quantum computing, but the practical merit is only shown when the amplitude is larger than 2. However, such high-amplitude cats have not been prepared due to the limitations rooted in the existing method. Here, we demonstrate a principle that a large SC-like state can be generated by the super… ▽ More Optical Schrodinger's cat (SC) is highly anticipated because of the potential of realizing fault-tolerant quantum computing, but the practical merit is only shown when the amplitude is larger than 2. However, such high-amplitude cats have not been prepared due to the limitations rooted in the existing method. Here, we demonstrate a principle that a large SC-like state can be generated by the superposition of two kittens in which two nearby coherent states interfere and grow to an enlarged coherent-like state. Further, we propose a scheme to breed the cat beyond the limitation in the former works with a high probability by realizing the superposition of two SCs in coupled waveguides. The principle and scheme demonstrated here provide a new perspective on understanding quantum superposition in phase space and a better solution for the efficient generation of SCs on chips. △ Less

Submitted 2 July, 2024; originally announced July 2024.

Manipulating Spectral Windings and Skin Modes through Nonconservative Couplings

Authors: Ningxin Kong, Chenghe Yu, Yilun Xu, Matteo Fadel, Xinyao Huang, Qiongyi He

Abstract: The discovery of the non-Hermitian skin effect (NHSE) has revolutionized our understanding of wave propagation in non-Hermitian systems, highlighting unexpected localization effects beyond conventional theories. Here, we discover that NHSE, accompanied by multitype spectral phases, can be induced by manipulating nonconservative couplings. By characterizing the spectra through the windings of the e… ▽ More The discovery of the non-Hermitian skin effect (NHSE) has revolutionized our understanding of wave propagation in non-Hermitian systems, highlighting unexpected localization effects beyond conventional theories. Here, we discover that NHSE, accompanied by multitype spectral phases, can be induced by manipulating nonconservative couplings. By characterizing the spectra through the windings of the energy bands, we demonstrate that band structures with identical, opposite, and even twisted windings can be achieved. These inequivalent types of spectra originate from the multichannel interference resulting from the interplay between conservative and nonconservative couplings. Associated with the multitype spectra, unipolar and bipolar NHSE with different eigenmode localizations can be observed. Additionally, our findings link the nonreciprocal transmission properties of the system to multiple spectral phases, indicating a connection with the skin modes. This paper paves new pathways for investigating non-Hermitian topological effects and manipulating nonreciprocal energy flow. △ Less

Submitted 13 November, 2024; v1 submitted 21 June, 2024; originally announced June 2024.

Comments: 12 pages, 6 figures

Journal ref: Physical Review A 110, 053507 (2024)

Genuine Multipartite Entanglement induced by a Thermal Acoustic Reservoir

Authors: Qing-Yang Qiu, Zhi-Guang Lu, Qiongyi He, Ying Wu, Xin-You Lü

Abstract: Genuine multipartite entanglement (GME) is not only fundamental interesting for the study of quantum-to-classical transition, but also is essential for realizing universal quantum computing and quantum networks. Here we investigate the multipartite entanglement (ME) dynamics in a linear chain of N LC resonators interacting optomechanically with a common thermal acoustic reservoir. By presenting th… ▽ More Genuine multipartite entanglement (GME) is not only fundamental interesting for the study of quantum-to-classical transition, but also is essential for realizing universal quantum computing and quantum networks. Here we investigate the multipartite entanglement (ME) dynamics in a linear chain of N LC resonators interacting optomechanically with a common thermal acoustic reservoir. By presenting the exact analytical solutions of system evolution, we predict the periodic generation of non-Gaussian ME, including the discrete and continuous variables entanglement. Interestingly, the GME is obtained even though the system is in a heat bath. The mechanism relies on the special acoustic environment featuring frequency comb structure. More importantly, our proposed model also allows the periodic generation of entangled multipartite cat states (MCSs), i.e., a typical GHZ state, with high fidelity. This work fundamentally broadens the fields of ME, and have wide applications in implementing thermal-noise-resistant quantum information processing and many-body quantum simulation. △ Less

Submitted 9 December, 2024; v1 submitted 19 June, 2024; originally announced June 2024.

Comments: 25 pages, 9 figures

Journal ref: Phys. Rev. B 110, L220301 (2024)

Quantum metrology with a squeezed Kerr oscillator

Authors: Jiajie Guo, Qiongyi He, Matteo Fadel

Abstract: We study the squeezing dynamics in a Kerr-nonlinear oscillator, and quantify the metrological usefulness of the resulting states. Even if the nonlinearity limits the attainable squeezing by making the evolution non-Gaussian, the states obtained still have a high quantum Fisher information for sensing displacements. However, contrary to the Gaussian case, the amplitude of the displacement cannot be… ▽ More We study the squeezing dynamics in a Kerr-nonlinear oscillator, and quantify the metrological usefulness of the resulting states. Even if the nonlinearity limits the attainable squeezing by making the evolution non-Gaussian, the states obtained still have a high quantum Fisher information for sensing displacements. However, contrary to the Gaussian case, the amplitude of the displacement cannot be estimated by simple quadrature measurements. Therefore, we propose the use of a measurement-after-interaction protocol where a linear quadrature measurement is preceded by an additional nonlinear evolution, and show the significant sensitivity enhancement that can be obtained. Our results are robust when considering realistic imperfections such as energy relaxation, and can be implemented in state-of-the-art experimental setups. △ Less

Submitted 17 June, 2024; originally announced June 2024.

Journal ref: Phys. Rev. A 109, 052604 (2024)

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.

Quantum Zeno Effect on Genuine Tripartite Nonlocality and Entanglement in Quantum Dissipative System

Authors: Zi-Yu Xiong, Yong-Jun Xiao, Ye-Qi Zhang, Qi-Liang He

Abstract: As a precious global resource in quantum information, genuine tripartite nonlocality(GTN) can be quantified by violating Svetlichny inequality. However, there is still no analytical expression for the general three-qubit states due to the difficulty of theoretical calculations. In this paper, we achieve highly accurate quantization of GTN for arbitrary three-qubit quantum states numerically. As an… ▽ More As a precious global resource in quantum information, genuine tripartite nonlocality(GTN) can be quantified by violating Svetlichny inequality. However, there is still no analytical expression for the general three-qubit states due to the difficulty of theoretical calculations. In this paper, we achieve highly accurate quantization of GTN for arbitrary three-qubit quantum states numerically. As an example, we study the dynamics of GTN and genuine tripartite entanglement(GTE) for the W state. Moreover, the complementarity of GTN is verified by examining the nonlocality between the tripartite and the bipartite. Finally, we also find a useful strategy to protect the correlation of GTN and GTE under decoherence by utilizing the Zeno effect. △ Less

Submitted 15 October, 2024; v1 submitted 29 May, 2024; originally announced May 2024.

Comments: 7 pages, 7 figures

Phase transition and multistability in Dicke dimer

Authors: Yilun Xu, Feng-Xiao Sun, Wei Zhang, Qiongyi He, Han Pu

Abstract: The exotic phase transitions and multistabilities in atom-cavity coupled systems have attracted tremendous interests recently. In this work, we investigate the effect of photon hopping between two Dicke cavities, which induces rich quantum phases for steady states and dynamic process. Starting from a generic dimer system where the two cavities are not necessarily identical, we analytically prove a… ▽ More The exotic phase transitions and multistabilities in atom-cavity coupled systems have attracted tremendous interests recently. In this work, we investigate the effect of photon hopping between two Dicke cavities, which induces rich quantum phases for steady states and dynamic process. Starting from a generic dimer system where the two cavities are not necessarily identical, we analytically prove all possible steady-state phases, which are confirmed by numerical calculations. We then focus on the special case with two identical cavities, where all the steady states are confirmed by exact solutions. We show that photon hopping is a convenient and powerful tool to manipulate the quantum phases and induce multistable behavior in this system. △ Less

Submitted 29 May, 2024; originally announced May 2024.

A nonlinear criterion for characterizing high-dimensional multipartite entanglement

Authors: Shuheng Liu, Qiongyi He, Marcus Huber, Giuseppe Vitagliano

Abstract: Understanding entanglement of potentially high-dimensional multipartite quantum systems is crucial across different disciplines in quantum sciences. We take inspiration from covariance matrix based techniques to derive a nonlinear criterion that can be used to lower bound the dimensionality vector of mixed quantum states, revealing both the level of multipartiteness and the dimensionality of the e… ▽ More Understanding entanglement of potentially high-dimensional multipartite quantum systems is crucial across different disciplines in quantum sciences. We take inspiration from covariance matrix based techniques to derive a nonlinear criterion that can be used to lower bound the dimensionality vector of mixed quantum states, revealing both the level of multipartiteness and the dimensionality of the entanglement in the quantum states. The technique is based on a system of inequalities that has to be satisfied by all quantum states with a given entanglement dimensionality vector, which can be checked via linear programming. We test our condition on paradigmatic classes of high-dimensional multipartite entangled states like imperfect Greenberger-Horne-Zeilinger (GHZ) states and find that, in comparison with other available criteria our method provides a significant advantage, which is enhanced especially in the case that the dimensions of the individual particles are different from each other. △ Less

Submitted 6 May, 2024; originally announced May 2024.

Optomechanical cooling with simultaneous intracavity and extracavity squeezed light

Authors: S. S. Zheng, F. X. Sun, M. Asjad, G. W. Zhang, J. Huo, J. Li, J. Zhou, Z. Ma, Q. Y. He

Abstract: We propose a novel and experimentally feasible approach to achieve high-efficiency ground-state cooling of a mechanical oscillator in an optomechanical system under the deeply unresolved sideband condition with the assistance of both intracavity and extracavity squeezing. In the scheme, a degenerate optical parametric amplifier is placed inside the optical cavity, generating the intracavity squeez… ▽ More We propose a novel and experimentally feasible approach to achieve high-efficiency ground-state cooling of a mechanical oscillator in an optomechanical system under the deeply unresolved sideband condition with the assistance of both intracavity and extracavity squeezing. In the scheme, a degenerate optical parametric amplifier is placed inside the optical cavity, generating the intracavity squeezing; besides, the optical cavity is driven by externally generated squeezing light, namely the extracavity squeezing. The quantum interference effect generated by intracavity squeezing and extracavity squeezing can completely suppress the non-resonant Stokes heating process while greatly enhancing the anti-Stokes cooling process. Therefore, the joint-squeezing scheme is capable of cooling the mechanical oscillators to their quantum ground state in a regime far away from the resolved sideband condition. Compared with other traditional optomechanical cooling schemes, the single-photon cooling rate in this joint-squeezing scheme can be tremendously enlarged by nearly three orders of magnitude. At the same time, the coupling strength required to achieve ground-state cooling can be significantly reduced. This scheme is promising for cooling large-mass and low-frequency mechanical oscillators, which provides a prerequisite for preparing and manipulating non-classical states in macroscopic quantum systems and lays a significant foundation for quantum manipulation. △ Less

Submitted 2 March, 2024; originally announced March 2024.

Comments: 12 pages, 5 figures

Journal ref: Phys. Rev. A 110, 063520 (2024)

Amplification of genuine tripartite nonlocality and entanglement in the Schwarzschild spacetime under decoherence

Authors: Chunyao Liu, Zhengwen Long, Qiliang He

Abstract: We investigate the amplification of the genuine tripartite nonlocality(GTN) and the genuine tripartite entanglement(GTE) of Dirac particles in the background of a Schwarzschild black hole by a local filtering operation under decoherence. It is shown that the physically accessible GTN will be completely destroyed by decoherence, which means that the physically accessible GTN will not exist in the s… ▽ More We investigate the amplification of the genuine tripartite nonlocality(GTN) and the genuine tripartite entanglement(GTE) of Dirac particles in the background of a Schwarzschild black hole by a local filtering operation under decoherence. It is shown that the physically accessible GTN will be completely destroyed by decoherence, which means that the physically accessible GTN will not exist in the system. Particularly, the local filtering operation can make the physically accessible GTN appear within a certain range of Hawking temperature, namely, the local filtering operation can cause the physically accessible GTN to be generated in the system coupled with the environment, which is not discovered before and is benefit for the quantum information processing. Furthermore, we also find that the physically accessible GTE approaches a stable value in the limit of infinite Hawking temperature for most cases, but if the decoherence parameter $p$ is less than 1, the ``sudden death'' of GTE will take place when the decoherence strength is large enough. It is worth noting that the nonzero stable value of GTE can be increased by performing the local filtering operation, even in the presence of decoherence. Finally, we explore the generation of physically inaccessible GTN and GTE of other tripartite subsystems under decoherence, it is shown that the physically inaccessible GTN cannot be produced, but the physically inaccessible GTE can be produced. In addition, we can see that the generated physically inaccessible GTE can be increased by applying the local filtering operation. △ Less

Submitted 20 May, 2024; v1 submitted 9 January, 2024; originally announced January 2024.

Comments: 11 pages, 9 figures. arXiv admin note: text overlap with arXiv:2201.02333 by other authors

Correlation-pattern-based Continuous-variable Entanglement Detection through Neural Networks

Authors: Xiaoting Gao, Mathieu Isoard, Fengxiao Sun, Carlos E. Lopetegui, Yu Xiang, Valentina Parigi, Qiongyi He, Mattia Walschaers

Abstract: Entanglement in continuous-variable non-Gaussian states provides irreplaceable advantages in many quantum information tasks. However, the sheer amount of information in such states grows exponentially and makes a full characterization impossible. Here, we develop a neural network that allows us to use correlation patterns to effectively detect continuous-variable entanglement through homodyne dete… ▽ More Entanglement in continuous-variable non-Gaussian states provides irreplaceable advantages in many quantum information tasks. However, the sheer amount of information in such states grows exponentially and makes a full characterization impossible. Here, we develop a neural network that allows us to use correlation patterns to effectively detect continuous-variable entanglement through homodyne detection. Using a recently defined stellar hierarchy to rank the states used for training, our algorithm works not only on any kind of Gaussian state but also on a whole class of experimentally achievable non-Gaussian states, including photon-subtracted states. With the same limited amount of data, our method provides higher accuracy than usual methods to detect entanglement based on maximum-likelihood tomography. Moreover, in order to visualize the effect of the neural network, we employ a dimension reduction algorithm on the patterns. This shows that a clear boundary appears between the entangled states and others after the neural network processing. In addition, these techniques allow us to compare different entanglement witnesses and understand their working. Our findings provide a new approach for experimental detection of continuous-variable quantum correlations without resorting to a full tomography of the state and confirm the exciting potential of neural networks in quantum information processing. △ Less

Submitted 31 October, 2023; originally announced October 2023.

Comments: 9 pages (incl. appendix), 6 figures, comments welcome!

Journal ref: Phys. Rev. Lett. 132, 220202 (2024)

Assisted metrology and preparation of macroscopic superpositions with split spin-squeezed states

Authors: Jiajie Guo, Fengxiao Sun, Qiongyi He, Matteo Fadel

Abstract: We analyse the conditional states in which one part of a split spin-squeezed state is left, upon performing a collective spin measurement on the other part. For appropriate measurement directions and outcomes, we see the possibility of obtaining states with high quantum Fisher information, even reaching the Heisenberg limit. This allows us to propose a metrological protocol that can outperform sta… ▽ More We analyse the conditional states in which one part of a split spin-squeezed state is left, upon performing a collective spin measurement on the other part. For appropriate measurement directions and outcomes, we see the possibility of obtaining states with high quantum Fisher information, even reaching the Heisenberg limit. This allows us to propose a metrological protocol that can outperform standard approaches, for example in a situation where the number of particles in the probe is bounded. The robustness of this protocol is investigated by considering realistic forms of noise present in cold-atom experiments, such as particle number fluctuations and imperfect detection. Ultimately, we show how this measurement-based state preparation approach can allow for the conditional (\ie heralded) preparation of spin Schrödinger's cat states even when the initial state before splitting is only mildly squeezed. △ Less

Submitted 19 October, 2023; originally announced October 2023.

Journal ref: Phys. Rev. A 108, 053327 (2023)

Certification of non-Gaussian Einstein-Podolsky-Rosen Steering

Authors: Mingsheng Tian, Zihang Zou, Da Zhang, David Barral, Kamel Bencheikh, Qiongyi He, Feng-Xiao Sun, Yu Xiang

Abstract: Non-Gaussian quantum states are a known necessary resource for reaching a quantum advantage and for violating Bell inequalities in continuous variable systems. As one kind of manifestation of quantum correlations, Einstein-Podolsky-Rosen (EPR) steering enables verification of shared entanglement even when one of the subsystems is not characterized. However, how to detect and classify such an effec… ▽ More Non-Gaussian quantum states are a known necessary resource for reaching a quantum advantage and for violating Bell inequalities in continuous variable systems. As one kind of manifestation of quantum correlations, Einstein-Podolsky-Rosen (EPR) steering enables verification of shared entanglement even when one of the subsystems is not characterized. However, how to detect and classify such an effect for non-Gaussian states is far from being well understood. Here, we present an efficient non-Gaussian steering criterion based on the high-order observables and conduct a systematic investigation into the hierarchy of non-Gaussian steering criteria. Moreover, we apply our criterion to three experimentally-relevant non-Gaussian states under realistic conditions and, in particular, propose a feasible scheme to create multi-component cat states with tunable size by performing a suitable high-order quadrature measurement on the steering party. Our work reveals the fundamental characteristics of non-Gaussianity and quantum correlations, and offers new insights to explore their applications in quantum information processing. △ Less

Submitted 26 August, 2023; originally announced August 2023.

Fast quantum state transfer and entanglement preparation in strongly coupled bosonic systems

Authors: Yilun Xu, Daoquan Zhu, Feng-Xiao Sun, Qiongyi He, Wei Zhang

Abstract: Continuous U(1) gauge symmetry, which guarantees the conservation of the total excitations in linear bosonic systems, will be broken when it comes to the strong-coupling regime where the rotation wave approximation (RWA) fails. Here we develop analytic solutions for multi-mode bosonic systems with XX-type couplings beyond RWA, and proposed a novel scheme to implement high-fidelity quantum state tr… ▽ More Continuous U(1) gauge symmetry, which guarantees the conservation of the total excitations in linear bosonic systems, will be broken when it comes to the strong-coupling regime where the rotation wave approximation (RWA) fails. Here we develop analytic solutions for multi-mode bosonic systems with XX-type couplings beyond RWA, and proposed a novel scheme to implement high-fidelity quantum state transfer (QST) and entanglement preparation (EP) with high speed. The scheme can be realized with designated coupling strength and pulse duration with which the excitation number keeps unchanged regardless of the breakdown of the global U(1) symmetry. In the QST tasks, we consider several typical quantum states and demonstrate that this method is robust against thermal noise and imperfections of experimental sequence. In the EP tasks, the scheme is successfully implemented for the preparation of Bell states and W-type states, within a shortest preparation time. △ Less

Submitted 29 October, 2023; v1 submitted 10 August, 2023; originally announced August 2023.

Comments: 30 pages, 8 figures

Journal ref: New J. Phys. 25, 113015 (2023)

Randomness Certification from Multipartite Quantum Steering for Arbitrary Dimensional Systems

Authors: Yi Li, Yu Xiang, Xiao-Dong Yu, H. Chau Nguyen, Otfried Gühne, Qiongyi He

Abstract: Entanglement in bipartite systems has been applied for the generation of secure random numbers, which are playing an important role in cryptography or scientific numerical simulations. Here, we propose to use multipartite entanglement distributed between trusted and untrusted parties for generating randomness of arbitrary dimensional systems. We show that the distributed structure of several parti… ▽ More Entanglement in bipartite systems has been applied for the generation of secure random numbers, which are playing an important role in cryptography or scientific numerical simulations. Here, we propose to use multipartite entanglement distributed between trusted and untrusted parties for generating randomness of arbitrary dimensional systems. We show that the distributed structure of several parties leads to additional protection against possible attacks by an eavesdropper, resulting in more secure randomness generated than in the corresponding bipartite scenario. Especially, randomness can be certified in the group of untrusted parties, even there is no randomness exists in either of them individually. We prove that the necessary and sufficient resource for quantum randomness in this scenario is multipartite quantum steering when two measurement settings are performed on the untrusted parties. However, the sufficiency no longer holds with more measurement settings. Finally, we apply our analysis to some experimentally realized states and show that more randomness can be extracted in comparison to the existing analysis. △ Less

Submitted 5 July, 2023; originally announced July 2023.

Comments: 14 pages, 5 figures

Journal ref: Phys. Rev. Lett. 132, 080201 (2024)

Generating optical cat states via quantum interference of multi-path free-electron-photons interactions

Authors: Feng-Xiao Sun, Yiqi Fang, Qiongyi He, Yunquan Liu

Abstract: The novel quantum effects induced by the free-electron-photons interaction have attracted increasing interest due to their potential applications in ultrafast quantum information processing. Here, we propose a scheme to generate optical cat states based on the quantum interference of multi-path free-electron-photons interactions that take place simultaneously with strong coupling strength. By perf… ▽ More The novel quantum effects induced by the free-electron-photons interaction have attracted increasing interest due to their potential applications in ultrafast quantum information processing. Here, we propose a scheme to generate optical cat states based on the quantum interference of multi-path free-electron-photons interactions that take place simultaneously with strong coupling strength. By performing a projection measurement on the electron, the state of light changes significantly from a coherent state into a non-Gaussian state with either Wigner negativity or squeezing property, both possess metrological power to achieve quantum advantage. More importantly, we show that the Wigner negativity oscillates with the coupling strength, and the optical cat states are successfully generated with high fidelity at all the oscillation peaks. This oscillation reveals the quantum interference effect of the multiple quantum pathways in the interaction of the electron with photons, by that various nonclassical states of light are promising to be fast prepared and manipulated. These findings inspire further exploration of emergent quantum phenomena and advanced quantum technologies with free electrons. △ Less

Submitted 22 June, 2023; originally announced June 2023.

Journal ref: Science Bulletin 68, 1366-1371 (2023)

Remote preparation of optical cat states based on Gaussian entanglement

Authors: Dongmei Han, Fengxiao Sun, Na Wang, Yu Xiang, Meihong Wang, Mingsheng Tian, Qiongyi He, Xiaolong Su

Abstract: Remote state preparation enables one to prepare and manipulate quantum state non-locally. As an essential quantum resource, optical cat state is usually prepared locally by subtracting photons from a squeezed vacuum state. For remote quantum information processing, it is essential to prepare and manipulate optical cat states remotely based on Gaussian entanglement, which remains a challenge. Here,… ▽ More Remote state preparation enables one to prepare and manipulate quantum state non-locally. As an essential quantum resource, optical cat state is usually prepared locally by subtracting photons from a squeezed vacuum state. For remote quantum information processing, it is essential to prepare and manipulate optical cat states remotely based on Gaussian entanglement, which remains a challenge. Here, we present experimental preparation of optical cat states based on a remotely distributed two-mode Gaussian entangled state in a lossy channel. By performing photon subtraction and homodyne projective measurement at Alice's station, an optical cat state is prepared remotely at Bob's station. Furthermore, the prepared cat state is rotated by changing Alice's measurement basis of homodyne detection, which demonstrates the remote manipulation of it. By distributing two modes of the two-mode Gaussian entangled state in lossy channels, we demonstrate that the remotely prepared cat state can tolerate much more loss in Alice's channel than that in Bob's channel. We also show that cat states with amplitudes larger than 2 can be prepared by increasing the squeezing level and subtracting photon numbers. Our results make a crucial step toward remote hybrid quantum information processing involving discrete- and continuous-variable techniques. △ Less

Submitted 18 April, 2023; originally announced April 2023.

Journal ref: Laser & Photonics Reviews 2300103 (2023)

Filtering one-way Einstein-Podolsky-Rosen steering

Authors: Ze-Yan Hao, Yan Wang, Jia-Kun Li, Yu Xiang, Qiong-Yi He, Zheng-Hao Liu, Mu Yang, Kai Sun, Jin-Shi Xu, Chuan-Feng Li, Guang-Can Guo

Abstract: Einstein-Podolsky-Rosen (EPR) steering, a fundamental concept of quantum nonlocality, describes one observer's capability to remotely affect another distant observer's state by local measurements. Unlike quantum entanglement and Bell nonlocality, both associated with the symmetric quantum correlation, EPR steering depicts the unique asymmetric property of quantum nonlocality. With the local filter… ▽ More Einstein-Podolsky-Rosen (EPR) steering, a fundamental concept of quantum nonlocality, describes one observer's capability to remotely affect another distant observer's state by local measurements. Unlike quantum entanglement and Bell nonlocality, both associated with the symmetric quantum correlation, EPR steering depicts the unique asymmetric property of quantum nonlocality. With the local filter operation in which some system components are discarded, quantum nonlocality can be distilled to enhance the nonlocal correlation, and even the hidden nonlocality can be activated. However, asymmetric quantum nonlocality in the filter operation still lacks a well-rounded investigation, especially considering the discarded parts where quantum nonlocal correlations may still exist with probabilities. Here, in both theory and experiment, we investigate the effect of reusing the discarded particles from local filter. We observe all configurations of EPR steering simultaneously and other intriguing evolution of asymmetric quantum nonlocality, such as reversing the direction of one-way EPR steering. This work provides a perspective to answer "What is the essential role of utilizing quantum steering as a resource?", and demonstrates a practical toolbox for manipulating asymmetric quantum systems with significant potential applications in quantum information tasks. △ Less

Submitted 3 January, 2024; v1 submitted 9 April, 2023; originally announced April 2023.

Comments: 11pages, 6figures