We introduce Quafu-Qcover,an open-source cloud-based software package developed for solving combinatorial optimization problems using quantum simulators and hardware backends.Quafu-Qcover provides a standardized and c...We introduce Quafu-Qcover,an open-source cloud-based software package developed for solving combinatorial optimization problems using quantum simulators and hardware backends.Quafu-Qcover provides a standardized and comprehensive workflow that utilizes the quantum approximate optimization algorithm(QAOA).It facilitates the automatic conversion of the original problem into a quadratic unconstrained binary optimization(QUBO)model and its corresponding Ising model,which can be subsequently transformed into a weight graph.The core of Qcover relies on a graph decomposition-based classical algorithm,which efficiently derives the optimal parameters for the shallow QAOA circuit.Quafu-Qcover incorporates a dedicated compiler capable of translating QAOA circuits into physical quantum circuits that can be executed on Quafu cloud quantum computers.Compared to a general-purpose compiler,our compiler demonstrates the ability to generate shorter circuit depths,while also exhibiting superior speed performance.Additionally,the Qcover compiler has the capability to dynamically create a library of qubits coupling substructures in real-time,utilizing the most recent calibration data from the superconducting quantum devices.This ensures that computational tasks can be assigned to connected physical qubits with the highest fidelity.The Quafu-Qcover allows us to retrieve quantum computing sampling results using a task ID at any time,enabling asynchronous processing.Moreover,it incorporates modules for results preprocessing and visualization,facilitating an intuitive display of solutions for combinatorial optimization problems.We hope that Quafu-Qcover can serve as an instructive illustration for how to explore application problems on the Quafu cloud quantum computers.展开更多
With the rapid advancement of quantum computing,hybrid quantum–classical machine learning has shown numerous potential applications at the current stage,with expectations of being achievable in the noisy intermediate...With the rapid advancement of quantum computing,hybrid quantum–classical machine learning has shown numerous potential applications at the current stage,with expectations of being achievable in the noisy intermediate-scale quantum(NISQ)era.Quantum reinforcement learning,as an indispensable study,has recently demonstrated its ability to solve standard benchmark environments with formally provable theoretical advantages over classical counterparts.However,despite the progress of quantum processors and the emergence of quantum computing clouds,implementing quantum reinforcement learning algorithms utilizing parameterized quantum circuits(PQCs)on NISQ devices remains infrequent.In this work,we take the first step towards executing benchmark quantum reinforcement problems on real devices equipped with at most 136 qubits on the BAQIS Quafu quantum computing cloud.The experimental results demonstrate that the policy agents can successfully accomplish objectives under modified conditions in both the training and inference phases.Moreover,we design hardware-efficient PQC architectures in the quantum model using a multi-objective evolutionary algorithm and develop a learning algorithm that is adaptable to quantum devices.We hope that the Quafu-RL can be a guiding example to show how to realize machine learning tasks by taking advantage of quantum computers on the quantum cloud platform.展开更多
Fundamental particles in nature can be classified as bosons or fermions,which satisfy their correspondent statistics.However,quasiparticles of condensed matter physics may be neither bosons nor fermions,but can be nam...Fundamental particles in nature can be classified as bosons or fermions,which satisfy their correspondent statistics.However,quasiparticles of condensed matter physics may be neither bosons nor fermions,but can be named as anyons satisfying a generalized statistics.These anyons can be related with topological phases of matter.Interestingly,anyons can be used to encode qubits to perform quantum computations with specific advantages in which the corresponding qubits are naturally fault tolerant due to topological protection.[1,2]This approach is called topological quantum computation.However,its implementation based on natural systems still seems far from realization.展开更多
Quantum coherence is a basic concept in quantum mechanics, representing one of the most fundamental characteristics that distinguishes quantum mechanics from classical physics. Quantum coherence is the basis for multi...Quantum coherence is a basic concept in quantum mechanics, representing one of the most fundamental characteristics that distinguishes quantum mechanics from classical physics. Quantum coherence is the basis for multi-particle interference and quantum entanglement. It is also the essential ingredient for various physical phenomena in quantum optics, quantum information, etc. In recent years, with the proposal of a quantum coherence measurement scheme based on a resource theory framework, quantum coherence as a quantum resource has been extensively investigated. This article reviews the resource theories of quantum coherence and introduces the important applications of quantum coherence in quantum computing,quantum information, and interdisciplinary fields, particularly in quantum thermodynamics and quantum biology. Quantum coherence and its applications are still being explored and developed. We hope this review can provide inspiration for relevant research.展开更多
Quantum computers promise to solve finite-temperature properties of quantum many-body systems,which is generally challenging for classical computers due to high computational complexities.Here,we report experimental p...Quantum computers promise to solve finite-temperature properties of quantum many-body systems,which is generally challenging for classical computers due to high computational complexities.Here,we report experimental preparations of Gibbs states and excited states of Heisenberg X X and X X Z models by using a 5-qubit programmable superconducting processor.In the experiments,we apply a hybrid quantum–classical algorithm to generate finite temperature states with classical probability models and variational quantum circuits.We reveal that the Hamiltonians can be fully diagonalized with optimized quantum circuits,which enable us to prepare excited states at arbitrary energy density.We demonstrate that the approach has a self-verifying feature and can estimate fundamental thermal observables with a small statistical error.Based on numerical results,we further show that the time complexity of our approach scales polynomially in the number of qubits,revealing its potential in solving large-scale problems.展开更多
The precise control and manipulation of the qubit state are vital for quantum simulation and quantum computation.In superconducting circuits,one notorious error comes from the crosstalk of microwave signals applied to...The precise control and manipulation of the qubit state are vital for quantum simulation and quantum computation.In superconducting circuits,one notorious error comes from the crosstalk of microwave signals applied to different qubit control lines.In this work,we present a method for the calibration and cancellation of the microwave crosstalk and experimentally demonstrate its effectiveness in a superconducting 10-qubit chain.The method is convenient and efficient especially for calibrating the microwave crosstalk with large amplitudes and variations,which can be performed successively to reduce the microwave crosstalk by two to three orders.The qubit chain with microwave driving is governed by one-dimensional(1D)Bose-Hubbard model in transverse field,which is nonintegrable and shows thermalization behaviour during the time evolution from certain initial states.Such thermalization process is observed with excellent agreement between experiment and theory further confirming the effective global cancellation of the microwave crosstalk.展开更多
We predict that the recently discovered quasi-one-dimensional superconductors, A2 Cr3As3 （A=K, Rb）, possess strong frustrated magnetic fluctuations and are nearby a novel in-out co-planar magnetic ground state. The ...We predict that the recently discovered quasi-one-dimensional superconductors, A2 Cr3As3 （A=K, Rb）, possess strong frustrated magnetic fluctuations and are nearby a novel in-out co-planar magnetic ground state. The frustrated magnetism is very sensitive to the c-axis lattice constant and can thus be suppressed by increasing pressure. Our results qualitatively explain strong non-Fermi liquid behaviors observed in the normal state of the superconductors as the intertwining between the magnetism and superconductivity can create a large quantum critical region in quasi-one-dimensional systems and also suggest that the materials share similar phase diagrams and superconducting mechanism with other unconventional superconductors, such as cuprates and iron-based superconductors.展开更多
The Loschmidt echo is a useful diagnostic for the perfection of quantum time-reversal process and the sensitivity of quantum evolution to small perturbations. The main challenge for measuring the Loschmidt echo is the...The Loschmidt echo is a useful diagnostic for the perfection of quantum time-reversal process and the sensitivity of quantum evolution to small perturbations. The main challenge for measuring the Loschmidt echo is the time reversal of a quantum evolution. In this work, we demonstrate the measurement of the Loschmidt echo in a superconducting 10-qubit system using Floquet engineering and discuss the imperfection of an initial Bell-state recovery arising from the next-nearestneighbor(NNN) coupling present in the qubit device. Our results show that the Loschmidt echo is very sensitive to small perturbations during quantum-state evolution, in contrast to the quantities like qubit population that is often considered in the time-reversal experiment. These properties may be employed for the investigation of multiqubit system concerning many-body decoherence and entanglement, etc., especially when devices with reduced or vanishing NNN coupling are used.展开更多
For a two-level atom in a lossy cavity, a scheme to manipulate the non-Markovian speedup dynamics has been pro- posed in the controllable environment （the lossy cavity field）. We mainly focus on the effects of the q...For a two-level atom in a lossy cavity, a scheme to manipulate the non-Markovian speedup dynamics has been pro- posed in the controllable environment （the lossy cavity field）. We mainly focus on the effects of the qubit--cavity detuning A and the qubit-cavity coupling strength k on the non-Markovian speedup evolution of an open system. By controlling the environment, i.e., tuning zl and , two dynamical crossovers from Markovian to non-Markovian and from no-speedup to speedup are achieved. Furthermore, it is clearly found that increasing the coupling strength k or detuning A in some cases can make the environmental non-Markovianity stronger and hence can lead to faster evolution of the open system.展开更多
The most basic local conversion is local operations and classical communications （LOCC）, which is also the most natural restriction in quantum information processing. We investigate the conversions between the groun...The most basic local conversion is local operations and classical communications （LOCC）, which is also the most natural restriction in quantum information processing. We investigate the conversions between the ground states in quantum critical systems via LOCC and propose a novel method to reveal the different convertibilities via majorization relation when a quantum phase transition occurs. The ground-state local convertibility in the one-dimensional transverse field Ising model is studied. It is shown that the LOCC convertibility changes nearly at the phase transition point. The relation between the order of quantum phase transitions and the LOCC convertibility is discussed. Our results are compared with the corresponding results by using the Renyi entropy and the LOCC convertibility with assisted entanglement.展开更多
We study the entanglement properties of the superposed state of orthogonal maximally entangled states. It is shown that the superposed state is maximally entangled and the superposed state is separable. The relation b...We study the entanglement properties of the superposed state of orthogonal maximally entangled states. It is shown that the superposed state is maximally entangled and the superposed state is separable. The relation between the superposed state and the mutually unbiased state is discussed.展开更多
An exact calculation method of local density of states （LDOS） in two-dimensional （2D） photonic crystals （PCs） is presented. In order to calculate the LDOS, the eigen-equation of magnetic field is first solved by...An exact calculation method of local density of states （LDOS） in two-dimensional （2D） photonic crystals （PCs） is presented. In order to calculate the LDOS, the eigen-equation of magnetic field is first solved by the plane-wave expansion method, then the eigen-modes of electric-field are obtained. There are two different ways to solve the eigen-equantion of magnetic field and three different ways to obtain the eigen-modes of the electric-field. In comparison of the numerical results from these different ways, an exact and fast method for calculating the LDOS in PCs is found. With use of this method, we investigate the LDOS of the 2D PCs consisting of a triangular lattice of cylinders. The results show the large LDOS is favorable to reside in higher dielectric-constant medium in high frequency region, rather than in lower dielectric-constant medium.展开更多
We study the reflection of a straight line or a billiard on a plane in an n-dimensional Minkowski space. It is found that the reflection law coincides with that defined with respect to confocal quadratic surfaces in p...We study the reflection of a straight line or a billiard on a plane in an n-dimensional Minkowski space. It is found that the reflection law coincides with that defined with respect to confocal quadratic surfaces in projective geometry. We then establish the full Poncelet theorem which holds in projective geometry in n-dimensional Minkowski space and in their quadratic surfaces including de Sitter and AdS spaces.展开更多
基金supported by the National Natural Science Foundation of China(Grant No.92365206)the support of the China Postdoctoral Science Foundation(Certificate Number:2023M740272)+1 种基金supported by the National Natural Science Foundation of China(Grant No.12247168)China Postdoctoral Science Foundation(Certificate Number:2022TQ0036)。
文摘We introduce Quafu-Qcover,an open-source cloud-based software package developed for solving combinatorial optimization problems using quantum simulators and hardware backends.Quafu-Qcover provides a standardized and comprehensive workflow that utilizes the quantum approximate optimization algorithm(QAOA).It facilitates the automatic conversion of the original problem into a quadratic unconstrained binary optimization(QUBO)model and its corresponding Ising model,which can be subsequently transformed into a weight graph.The core of Qcover relies on a graph decomposition-based classical algorithm,which efficiently derives the optimal parameters for the shallow QAOA circuit.Quafu-Qcover incorporates a dedicated compiler capable of translating QAOA circuits into physical quantum circuits that can be executed on Quafu cloud quantum computers.Compared to a general-purpose compiler,our compiler demonstrates the ability to generate shorter circuit depths,while also exhibiting superior speed performance.Additionally,the Qcover compiler has the capability to dynamically create a library of qubits coupling substructures in real-time,utilizing the most recent calibration data from the superconducting quantum devices.This ensures that computational tasks can be assigned to connected physical qubits with the highest fidelity.The Quafu-Qcover allows us to retrieve quantum computing sampling results using a task ID at any time,enabling asynchronous processing.Moreover,it incorporates modules for results preprocessing and visualization,facilitating an intuitive display of solutions for combinatorial optimization problems.We hope that Quafu-Qcover can serve as an instructive illustration for how to explore application problems on the Quafu cloud quantum computers.
基金supported by the Beijing Academy of Quantum Information Sciencessupported by the National Natural Science Foundation of China(Grant No.92365206)+2 种基金the support of the China Postdoctoral Science Foundation(Certificate Number:2023M740272)supported by the National Natural Science Foundation of China(Grant No.12247168)China Postdoctoral Science Foundation(Certificate Number:2022TQ0036)。
文摘With the rapid advancement of quantum computing,hybrid quantum–classical machine learning has shown numerous potential applications at the current stage,with expectations of being achievable in the noisy intermediate-scale quantum(NISQ)era.Quantum reinforcement learning,as an indispensable study,has recently demonstrated its ability to solve standard benchmark environments with formally provable theoretical advantages over classical counterparts.However,despite the progress of quantum processors and the emergence of quantum computing clouds,implementing quantum reinforcement learning algorithms utilizing parameterized quantum circuits(PQCs)on NISQ devices remains infrequent.In this work,we take the first step towards executing benchmark quantum reinforcement problems on real devices equipped with at most 136 qubits on the BAQIS Quafu quantum computing cloud.The experimental results demonstrate that the policy agents can successfully accomplish objectives under modified conditions in both the training and inference phases.Moreover,we design hardware-efficient PQC architectures in the quantum model using a multi-objective evolutionary algorithm and develop a learning algorithm that is adaptable to quantum devices.We hope that the Quafu-RL can be a guiding example to show how to realize machine learning tasks by taking advantage of quantum computers on the quantum cloud platform.
文摘Fundamental particles in nature can be classified as bosons or fermions,which satisfy their correspondent statistics.However,quasiparticles of condensed matter physics may be neither bosons nor fermions,but can be named as anyons satisfying a generalized statistics.These anyons can be related with topological phases of matter.Interestingly,anyons can be used to encode qubits to perform quantum computations with specific advantages in which the corresponding qubits are naturally fault tolerant due to topological protection.[1,2]This approach is called topological quantum computation.However,its implementation based on natural systems still seems far from realization.
基金Project supported by the National Natural Science Foundation of China (Grant No. 12175179)the Peng Huaiwu Center for Fundamental Theory (Grant No. 12247103)the Natural Science Basic Research Program of Shaanxi Province (Grant Nos. 2021JCW-19 and 2019JQ-863)。
文摘Quantum coherence is a basic concept in quantum mechanics, representing one of the most fundamental characteristics that distinguishes quantum mechanics from classical physics. Quantum coherence is the basis for multi-particle interference and quantum entanglement. It is also the essential ingredient for various physical phenomena in quantum optics, quantum information, etc. In recent years, with the proposal of a quantum coherence measurement scheme based on a resource theory framework, quantum coherence as a quantum resource has been extensively investigated. This article reviews the resource theories of quantum coherence and introduces the important applications of quantum coherence in quantum computing,quantum information, and interdisciplinary fields, particularly in quantum thermodynamics and quantum biology. Quantum coherence and its applications are still being explored and developed. We hope this review can provide inspiration for relevant research.
基金Project supported by the State Key Development Program for Basic Research of China(Grant No.2017YFA0304300)the National Natural Science Foundation of China(Grant Nos.11934018,11747601,and 11975294)+4 种基金Strategic Priority Research Program of Chinese Academy of Sciences(Grant No.XDB28000000)Scientific Instrument Developing Project of Chinese Academy of Sciences(Grant No.YJKYYQ20200041)Beijing Natural Science Foundation(Grant No.Z200009)the Key-Area Research and Development Program of Guangdong Province,China(Grant No.2020B0303030001)Chinese Academy of Sciences(Grant No.QYZDB-SSW-SYS032)。
文摘Quantum computers promise to solve finite-temperature properties of quantum many-body systems,which is generally challenging for classical computers due to high computational complexities.Here,we report experimental preparations of Gibbs states and excited states of Heisenberg X X and X X Z models by using a 5-qubit programmable superconducting processor.In the experiments,we apply a hybrid quantum–classical algorithm to generate finite temperature states with classical probability models and variational quantum circuits.We reveal that the Hamiltonians can be fully diagonalized with optimized quantum circuits,which enable us to prepare excited states at arbitrary energy density.We demonstrate that the approach has a self-verifying feature and can estimate fundamental thermal observables with a small statistical error.Based on numerical results,we further show that the time complexity of our approach scales polynomially in the number of qubits,revealing its potential in solving large-scale problems.
基金the Key-Area Research and Development Program of Guangdong Province,China(Grant No.2018B030326001)the National Natural Science Foundation of China(Grant No.11874063),the National Natural Science Foundation of China(Grant No.11890704)+3 种基金the National Natural Science Foundation of China(Grant Nos.11934018 and T2121001)the Natural Science Foundation of Beijing(Grant No.Z190012)Strategic Priority Research Program of the Chinese Academy of Sciences(Grant No.XDB28000000)Beijing Natural Science Foundation(Grant No.Z200009)。
文摘The precise control and manipulation of the qubit state are vital for quantum simulation and quantum computation.In superconducting circuits,one notorious error comes from the crosstalk of microwave signals applied to different qubit control lines.In this work,we present a method for the calibration and cancellation of the microwave crosstalk and experimentally demonstrate its effectiveness in a superconducting 10-qubit chain.The method is convenient and efficient especially for calibrating the microwave crosstalk with large amplitudes and variations,which can be performed successively to reduce the microwave crosstalk by two to three orders.The qubit chain with microwave driving is governed by one-dimensional(1D)Bose-Hubbard model in transverse field,which is nonintegrable and shows thermalization behaviour during the time evolution from certain initial states.Such thermalization process is observed with excellent agreement between experiment and theory further confirming the effective global cancellation of the microwave crosstalk.
基金Supported by the National Basic Research Program of China under Grant Nos 2010CB922904,2012CV821400 and2015CB921300the National Natural Science Foundation of China under Grant Nos 1190024,11175248 and 11104339the Strategic Priority Research Program of Chinese Academy of Sciences under Grant No XDB07000000
文摘We predict that the recently discovered quasi-one-dimensional superconductors, A2 Cr3As3 （A=K, Rb）, possess strong frustrated magnetic fluctuations and are nearby a novel in-out co-planar magnetic ground state. The frustrated magnetism is very sensitive to the c-axis lattice constant and can thus be suppressed by increasing pressure. Our results qualitatively explain strong non-Fermi liquid behaviors observed in the normal state of the superconductors as the intertwining between the magnetism and superconductivity can create a large quantum critical region in quasi-one-dimensional systems and also suggest that the materials share similar phase diagrams and superconducting mechanism with other unconventional superconductors, such as cuprates and iron-based superconductors.
基金supported in part by the Key-Area Research and Development Program of Guang-Dong Province, China (Grant No. 2018B030326001)the National Key R&D Program of China (Grant No. 2017YFA0304300)+5 种基金supported by the Japan Society for the Promotion of Science (JSPS) (Postdoctoral Fellowship via Grant No. P19326, and KAKENHI via Grant No. JP19F19326)support from the Natural Science Foundation of Beijing, China (Grant No. Z190012)the National Natural Science Foundation of of China (Grant No. 11890704)support from the National Natural Science Foundation of China (Grant No. T2121001)Strategic Priority Research Program of Chinese Academy of Sciences (Grant No. XDB28000000)Beijing Natural Science Foundation, China (Grant No. Z200009)。
文摘The Loschmidt echo is a useful diagnostic for the perfection of quantum time-reversal process and the sensitivity of quantum evolution to small perturbations. The main challenge for measuring the Loschmidt echo is the time reversal of a quantum evolution. In this work, we demonstrate the measurement of the Loschmidt echo in a superconducting 10-qubit system using Floquet engineering and discuss the imperfection of an initial Bell-state recovery arising from the next-nearestneighbor(NNN) coupling present in the qubit device. Our results show that the Loschmidt echo is very sensitive to small perturbations during quantum-state evolution, in contrast to the quantities like qubit population that is often considered in the time-reversal experiment. These properties may be employed for the investigation of multiqubit system concerning many-body decoherence and entanglement, etc., especially when devices with reduced or vanishing NNN coupling are used.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.11647171,61675115,and 91536108)
文摘For a two-level atom in a lossy cavity, a scheme to manipulate the non-Markovian speedup dynamics has been pro- posed in the controllable environment （the lossy cavity field）. We mainly focus on the effects of the qubit--cavity detuning A and the qubit-cavity coupling strength k on the non-Markovian speedup evolution of an open system. By controlling the environment, i.e., tuning zl and , two dynamical crossovers from Markovian to non-Markovian and from no-speedup to speedup are achieved. Furthermore, it is clearly found that increasing the coupling strength k or detuning A in some cases can make the environmental non-Markovianity stronger and hence can lead to faster evolution of the open system.
基金Supported by the National Basic Research Program of China under Grant No 2010CB922904, and the National Natural Science Foundation of China under Grant No 11175248. The authors thank Cao Jun-Peng, Wang Dong and Zeng Yu for their valuable discussions.
文摘The most basic local conversion is local operations and classical communications （LOCC）, which is also the most natural restriction in quantum information processing. We investigate the conversions between the ground states in quantum critical systems via LOCC and propose a novel method to reveal the different convertibilities via majorization relation when a quantum phase transition occurs. The ground-state local convertibility in the one-dimensional transverse field Ising model is studied. It is shown that the LOCC convertibility changes nearly at the phase transition point. The relation between the order of quantum phase transitions and the LOCC convertibility is discussed. Our results are compared with the corresponding results by using the Renyi entropy and the LOCC convertibility with assisted entanglement.
基金Supported by the National Natural Science Foundation of China under Grant Nos 10974247, 10775176 and 10975181, and the National Basic Research Program of China under Grant No 2010CB922904.
文摘We study the entanglement properties of the superposed state of orthogonal maximally entangled states. It is shown that the superposed state is maximally entangled and the superposed state is separable. The relation between the superposed state and the mutually unbiased state is discussed.
基金Supported by the National Basic Research Program of China under Grant Nos 2006CB921706 and 2010CB923200, and the National Natural Science Foundation of China under Grant Nos 10725420 and U0934002.
文摘An exact calculation method of local density of states （LDOS） in two-dimensional （2D） photonic crystals （PCs） is presented. In order to calculate the LDOS, the eigen-equation of magnetic field is first solved by the plane-wave expansion method, then the eigen-modes of electric-field are obtained. There are two different ways to solve the eigen-equantion of magnetic field and three different ways to obtain the eigen-modes of the electric-field. In comparison of the numerical results from these different ways, an exact and fast method for calculating the LDOS in PCs is found. With use of this method, we investigate the LDOS of the 2D PCs consisting of a triangular lattice of cylinders. The results show the large LDOS is favorable to reside in higher dielectric-constant medium in high frequency region, rather than in lower dielectric-constant medium.
基金Supported by the National Natural Science Foundation of China under Grant Nos 10674162 and 10575080, and the National Basic Research Programme of China under Grant No 2006CB921107.
文摘We study the reflection of a straight line or a billiard on a plane in an n-dimensional Minkowski space. It is found that the reflection law coincides with that defined with respect to confocal quadratic surfaces in projective geometry. We then establish the full Poncelet theorem which holds in projective geometry in n-dimensional Minkowski space and in their quadratic surfaces including de Sitter and AdS spaces.
