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
Realization of a flexible and tunable coupling scheme among qubits is critical for scalable quantum information processing.Here,we design and characterize a tunable coupling element based on Josephson junction,which c...Realization of a flexible and tunable coupling scheme among qubits is critical for scalable quantum information processing.Here,we design and characterize a tunable coupling element based on Josephson junction,which can be adapted to an all-to-all connected circuit architecture where multiple Xmon qubits couple to a common coplanar waveguide resonator.The coupling strength is experimentally verified to be adjustable from 0 MHz to about 40 MHz,and the qubit lifetime can still be up to 12μs in the presence of the coupling element.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
Hybrid quantum system of negatively charged nitrogen–vacancy(NV^-) centers in diamond and superconducting qubits provide the possibility to extend the performances of both systems. In this work, we numerically simu...Hybrid quantum system of negatively charged nitrogen–vacancy(NV^-) centers in diamond and superconducting qubits provide the possibility to extend the performances of both systems. In this work, we numerically simulate the coupling strength between NV^-ensembles and superconducting flux qubits and obtain a lower bound of 1016cm^(-3) for NV^-concentration to achieve a sufficiently strong coupling of 10 MHz when the gap between NV^-ensemble and flux qubit is 0. Moreover, we create NV^-ensembles in different types of diamonds by14^(N+)and12(C+)ion implantation, electron irradiation, and high temperature annealing. We obtain an NV^-concentration of 1.05 × 1016cm^(-3) in the diamond with1-ppm nitrogen impurity, which is expected to have a long coherence time for the low nitrogen impurity concentration. This shows a step toward performance improvement of flux qubit-NV^-hybrid system.展开更多
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Project supported by the National Key Research and Development Program of China(Grant Nos.2017YFA0304300 and 2016YFA0300600)the National Natural Science Foundation of China(Grant Nos.11725419 and 11434008)the Strategic Priority Research Program of Chinese Academy of Sciences(Grant No.XDB28000000)
文摘Realization of a flexible and tunable coupling scheme among qubits is critical for scalable quantum information processing.Here,we design and characterize a tunable coupling element based on Josephson junction,which can be adapted to an all-to-all connected circuit architecture where multiple Xmon qubits couple to a common coplanar waveguide resonator.The coupling strength is experimentally verified to be adjustable from 0 MHz to about 40 MHz,and the qubit lifetime can still be up to 12μs in the presence of the coupling element.
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 in part by the National Natural Science Foundation of China(Grant Nos.91321208,11574386,11374344,and 11574380)the National Basic Research Program of China(Grant Nos.2014CB921401 and 2016YFA0300601)the Strategic Priority Research Program of the Chinese Academy of Sciences(Grant No.XDB07010300)
文摘Hybrid quantum system of negatively charged nitrogen–vacancy(NV^-) centers in diamond and superconducting qubits provide the possibility to extend the performances of both systems. In this work, we numerically simulate the coupling strength between NV^-ensembles and superconducting flux qubits and obtain a lower bound of 1016cm^(-3) for NV^-concentration to achieve a sufficiently strong coupling of 10 MHz when the gap between NV^-ensemble and flux qubit is 0. Moreover, we create NV^-ensembles in different types of diamonds by14^(N+)and12(C+)ion implantation, electron irradiation, and high temperature annealing. We obtain an NV^-concentration of 1.05 × 1016cm^(-3) in the diamond with1-ppm nitrogen impurity, which is expected to have a long coherence time for the low nitrogen impurity concentration. This shows a step toward performance improvement of flux qubit-NV^-hybrid system.