Superconducting circuits based on Josephson junctions are regarded as one of the most promising technologies for the implementation of scalable quantum computers.This review presents the basic principles of supercondu...Superconducting circuits based on Josephson junctions are regarded as one of the most promising technologies for the implementation of scalable quantum computers.This review presents the basic principles of superconducting qubits and shows the progress of quantum computing and quantum simulation based on superconducting qubits in recent years.The experimental realization of gate operations,readout,error correction codes,as well as some quantum algorithms are summarized,followed by an introduction of quantum simulation.And then some important applications in fields including condensed matter physics,quantum annealing,and quantum chemistry are discussed.展开更多
As a valid tool for solving ground state problems,imaginary time evolution(ITE)is widely used in physical and chemical simulations.Different ITE-based algorithms in their quantum counterpart have recently been propose...As a valid tool for solving ground state problems,imaginary time evolution(ITE)is widely used in physical and chemical simulations.Different ITE-based algorithms in their quantum counterpart have recently been proposed and applied to some real systems.We experimentally realize the variational-based quantum imaginary time evolution(QITE)algorithm to simulate the ground state energy of hydrogen(H_2)and lithium hydride(Li H)molecules in a superconducting qubit system.The H_2 molecule is directly simulated using the 3-qubit circuit with unitary-coupled clusters(UCC)ansatz.We also combine QITE with the cluster mean-field(CMF)method to obtain an effective Hamiltonian.The Li H molecule is correspondingly simulated using the 3-qubit circuit with hardware-efficient ansatz.For comparison,the Li H molecule is also directly simulated using the 4-qubit circuit with UCC ansatz at the equilibrium point.All the experimental results show a convergence within 4 iterations,with high-fidelity ground state energy obtained.For a more complex system in the future,the CMF may allow further grouping of interactions to obtain an effective Hamiltonian,then the hybrid QITE algorithm can possibly simulate a relatively large-scale system with fewer qubits.展开更多
Solid-state quantum computation station belongs to the group 2 of manipulation of quantum state in the Synergetic Extreme Condition User Facility. Here we will first outline the research background, aspects, and objec...Solid-state quantum computation station belongs to the group 2 of manipulation of quantum state in the Synergetic Extreme Condition User Facility. Here we will first outline the research background, aspects, and objectives of the station, followed by a discussion of the recent scientific as well as technological progress in this field based on similar experimental facilities to be constructed in the station. Finally, a brief summary and research perspective will be presented.展开更多
One of the key features required to realize fault-tolerant quantum computation is the robustness of quantum gates against errors.Since geometric quantum gate is naturally insensitivity to noise,it appears to be a prom...One of the key features required to realize fault-tolerant quantum computation is the robustness of quantum gates against errors.Since geometric quantum gate is naturally insensitivity to noise,it appears to be a promising routine to achieve high-fidelity,robust quantum gates.The implementation of geometric quantum gate however faces some troubles such as its complex interaction among multiple energy levels.Moreover,traditional geometric schemes usually take more time than equivalent dynamical ones.Here,we experimentally demonstrate a geometric gate scheme with the time-optimal control(TOC)technique in a superconducting quantum circuit.With a transmon qubit and operations restricted to two computational levels,we implement a set of geometric gates which exhibit better robustness features against control errors than the dynamical counterparts.The measured fidelities of TOC X gate and X/2 gate are 99.81%and 99.79%respectively.Our work shows a promising routine toward scalable fault-tolerant quantum computation.展开更多
High-fidelity initialization,manipulation,and measurement of qubits are important in quantum computing.For the Google’s Sycamore processor,the gate fidelity of single-and two-qubit logic operations has improved to>...High-fidelity initialization,manipulation,and measurement of qubits are important in quantum computing.For the Google’s Sycamore processor,the gate fidelity of single-and two-qubit logic operations has improved to>99.6%,whereas single-shot measurement fidelity remains at the level of 97%,which severely limits the ap-plication of the superconducting approach to large-scale quantum computing.The current measurement scheme relies on the dispersive interaction between the qubit and the readout resonator,which was proposed back in 2004.However,the measurement fidelity is limited by the trade-offbetween the state separation and relax-ation time of the two-level system.Recently,an exciting phenomenon was observed experimentally,wherein the separation-decay limit could be alleviated by exploiting the cascade decay nature of the higher levels;however,the mechanism and effectiveness of this phenomenon are still unclear.Herein,we present a theoretical tool to extract different types of errors in high-level states encoding dispersive measurement.For the realistic parame-ters of Google’s Sycamore processor,the use of state|2>is sufficient to suppress 92%of the decay readout error on average,where the total readout error is dominated by the background thermal excitation.We also show counter-intuitively that,the assistance of high-level states is effective in the measurement of logic 0,where there is no decay process.展开更多
Superconducting transmon qubits are the leading platform in solid-state quantum computing and quantum simulation applications.In this work,we develop a fabrication process for the transmon multiqubit device with a nio...Superconducting transmon qubits are the leading platform in solid-state quantum computing and quantum simulation applications.In this work,we develop a fabrication process for the transmon multiqubit device with a niobium base layer,shadow-evaporated Josephson junctions,and airbridges across the qubit control lines to suppress crosstalk.Our results show that these multiqubit devices have well-characterized readout resonators,and that the energy relaxation and Ramsey(spin-echo)dephasing times are up to∼40µs and 14(47)µs,respectively.We perform single-qubit gate operations that demonstrate a maximum gate fidelity of 99.97%.In addition,two-qubit vacuum Rabi oscillations are measured to evaluate the coupling strength between qubits,and the crosstalk among qubits is found to be less than 1%with the fabricated airbridges.Further improvements in qubit coherence performance using this fabrication process are also discussed.展开更多
Superconducting quantum bits （qubits） and circuits are the leading candidate for the implementation of solid-state quantum computation. They have also been widely used in a variety of studies of quantum physics, ato...Superconducting quantum bits （qubits） and circuits are the leading candidate for the implementation of solid-state quantum computation. They have also been widely used in a variety of studies of quantum physics, atomic physics, quantum optics, and quantum simulation. In this article, we will present an overview of the basic principles of the superconducting qubits, including the phase, flux, charge, and transmon （Xmon） qubits, and the progress achieved so far concerning the improvements of the device design and quantum coherence property. Experimental studies in various research fields using the superconducting qubits and circuits will be briefly reviewed.展开更多
The Hamiltonian of a superconducting charge qubit with a configuration of dc SQUID contains an interac-tion between the LC oscillator part and charge qubit.This interaction may leads to quantum state collapse and revi...The Hamiltonian of a superconducting charge qubit with a configuration of dc SQUID contains an interac-tion between the LC oscillator part and charge qubit.This interaction may leads to quantum state collapse and revivalwhich degrades the charge qubits and leads to serious decoherence.An analysis shows that the existing charge qubitparameters do not lead to this phenomenon,which is very good for the superconducting charge展开更多
Motivated by recent realizations of two-dimensional(2D)superconducting-qubit lattices,we propose a protocol to simulate Hofstadter butterfly with synthetic gauge fields in superconducting circuits.Based on the existin...Motivated by recent realizations of two-dimensional(2D)superconducting-qubit lattices,we propose a protocol to simulate Hofstadter butterfly with synthetic gauge fields in superconducting circuits.Based on the existing 2D superconducting-qubit lattices,we construct a generalized Hofstadter model on zigzag lattices,which has a fractal energy spectrum similar to the original Hofstadter butterfly.By periodically modulating the resonant frequencies of qubits,we engineer a synthetic gauge field to mimic the generalized Hofstadter Hamiltonian.A spectroscopic method is used to demonstrate the Hofstadter butterfly from the time evolutions of experimental observables.We numerically simulate the dynamics of the system with realistic parameters,and the results show a butterfly spectrum clearly.Our proposal provides a promising way to realize the Hofstadter butterfly on the latest 2D superconducting-qubit lattices and will stimulate the quantum simulation of novel properties induced by magnetic fields in superconducting circuits.展开更多
Geometric phases are only dependent on evolution paths but independent of evolution details so that they possess some intrinsic noise-resilience features. Based on different geometric phases, various quantum gates hav...Geometric phases are only dependent on evolution paths but independent of evolution details so that they possess some intrinsic noise-resilience features. Based on different geometric phases, various quantum gates have been proposed, such as nonadiabatic geometric gates based on nonadiabatic Abelian geometric phases and nonadiabatic holonomic gates based on nonadiabatic nonAbelian geometric phases. Up to now, nonadiabatic holonomic one-qubit gates have been experimentally demonstrated with superconducting transmons, where the three lowest levels are all utilized in operation. However, the second excited state of transmons has a relatively short coherence time, which results in a decreased fidelity of quantum gates. Here, we experimentally realize Abelian-geometric-phase-based nonadiabatic geometric one-qubit gates with a superconducting Xmon qubit. The realization is performed on the two lowest levels of an Xmon qubit and thus avoids the influence from the short coherence time of the second excited state. The experimental result indicates that the average fidelities of single-qubit gates can be up to 99.6% and 99.7% characterized by quantum process tomography and randomized benchmarking.展开更多
基金Project supported by the National Natural Science Foundation of China(Grant Nos.11653001,11653004,and 60836001).
文摘Superconducting circuits based on Josephson junctions are regarded as one of the most promising technologies for the implementation of scalable quantum computers.This review presents the basic principles of superconducting qubits and shows the progress of quantum computing and quantum simulation based on superconducting qubits in recent years.The experimental realization of gate operations,readout,error correction codes,as well as some quantum algorithms are summarized,followed by an introduction of quantum simulation.And then some important applications in fields including condensed matter physics,quantum annealing,and quantum chemistry are discussed.
基金supported by the National Natural Science Foundation of China(Grant Nos.12074336,and 11934010)the National Key Research and Development Program of China(Grant No.2019YFA0308602)+1 种基金the Fundamental Research Funds for the Central Universities in China(Grant No.2020XZZX002-01)the funding support from Tencent Corporation。
文摘As a valid tool for solving ground state problems,imaginary time evolution(ITE)is widely used in physical and chemical simulations.Different ITE-based algorithms in their quantum counterpart have recently been proposed and applied to some real systems.We experimentally realize the variational-based quantum imaginary time evolution(QITE)algorithm to simulate the ground state energy of hydrogen(H_2)and lithium hydride(Li H)molecules in a superconducting qubit system.The H_2 molecule is directly simulated using the 3-qubit circuit with unitary-coupled clusters(UCC)ansatz.We also combine QITE with the cluster mean-field(CMF)method to obtain an effective Hamiltonian.The Li H molecule is correspondingly simulated using the 3-qubit circuit with hardware-efficient ansatz.For comparison,the Li H molecule is also directly simulated using the 4-qubit circuit with UCC ansatz at the equilibrium point.All the experimental results show a convergence within 4 iterations,with high-fidelity ground state energy obtained.For a more complex system in the future,the CMF may allow further grouping of interactions to obtain an effective Hamiltonian,then the hybrid QITE algorithm can possibly simulate a relatively large-scale system with fewer qubits.
文摘Solid-state quantum computation station belongs to the group 2 of manipulation of quantum state in the Synergetic Extreme Condition User Facility. Here we will first outline the research background, aspects, and objectives of the station, followed by a discussion of the recent scientific as well as technological progress in this field based on similar experimental facilities to be constructed in the station. Finally, a brief summary and research perspective will be presented.
基金Project supported by the Key Research and Development Program of Guangdong Province,China(Grant No.2018B030326001)the National Natural Science Foundation of China(Grant Nos.11474152,12074179,U21A20436,and 61521001)the Natural Science Foundation of Jiangsu Province,China(Grant No.BE2021015-1)。
文摘One of the key features required to realize fault-tolerant quantum computation is the robustness of quantum gates against errors.Since geometric quantum gate is naturally insensitivity to noise,it appears to be a promising routine to achieve high-fidelity,robust quantum gates.The implementation of geometric quantum gate however faces some troubles such as its complex interaction among multiple energy levels.Moreover,traditional geometric schemes usually take more time than equivalent dynamical ones.Here,we experimentally demonstrate a geometric gate scheme with the time-optimal control(TOC)technique in a superconducting quantum circuit.With a transmon qubit and operations restricted to two computational levels,we implement a set of geometric gates which exhibit better robustness features against control errors than the dynamical counterparts.The measured fidelities of TOC X gate and X/2 gate are 99.81%and 99.79%respectively.Our work shows a promising routine toward scalable fault-tolerant quantum computation.
基金University of Science and Technology of China has submitted patent applications related to the subject to Chinese National Intel-lectual Property Administration on 05 Feb 2020(202010081148.8,PCT/CN2020/074321),the authors are part of inventors.
文摘High-fidelity initialization,manipulation,and measurement of qubits are important in quantum computing.For the Google’s Sycamore processor,the gate fidelity of single-and two-qubit logic operations has improved to>99.6%,whereas single-shot measurement fidelity remains at the level of 97%,which severely limits the ap-plication of the superconducting approach to large-scale quantum computing.The current measurement scheme relies on the dispersive interaction between the qubit and the readout resonator,which was proposed back in 2004.However,the measurement fidelity is limited by the trade-offbetween the state separation and relax-ation time of the two-level system.Recently,an exciting phenomenon was observed experimentally,wherein the separation-decay limit could be alleviated by exploiting the cascade decay nature of the higher levels;however,the mechanism and effectiveness of this phenomenon are still unclear.Herein,we present a theoretical tool to extract different types of errors in high-level states encoding dispersive measurement.For the realistic parame-ters of Google’s Sycamore processor,the use of state|2>is sufficient to suppress 92%of the decay readout error on average,where the total readout error is dominated by the background thermal excitation.We also show counter-intuitively that,the assistance of high-level states is effective in the measurement of logic 0,where there is no decay process.
基金supported by the National Key R&D Program of China(Grant No.2016YFA0300601)the National Natural Science Foundation of China(Grant Nos.11934018 and 11874063)+1 种基金the Strategic Priority Research Program of the Chinese Academy of Sciences(Grant No.XDB28000000)the Key-Area Research and Development Program of GuangDong Province,China(Grant No.2018B030326001)。
文摘Superconducting transmon qubits are the leading platform in solid-state quantum computing and quantum simulation applications.In this work,we develop a fabrication process for the transmon multiqubit device with a niobium base layer,shadow-evaporated Josephson junctions,and airbridges across the qubit control lines to suppress crosstalk.Our results show that these multiqubit devices have well-characterized readout resonators,and that the energy relaxation and Ramsey(spin-echo)dephasing times are up to∼40µs and 14(47)µs,respectively.We perform single-qubit gate operations that demonstrate a maximum gate fidelity of 99.97%.In addition,two-qubit vacuum Rabi oscillations are measured to evaluate the coupling strength between qubits,and the crosstalk among qubits is found to be less than 1%with the fabricated airbridges.Further improvements in qubit coherence performance using this fabrication process are also discussed.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.91321208 and 11674380)the National Key Basic Research Program of the Ministry of Science and Technology of China(Grant Nos.2014CB921202,2015CB921104,and 2016YFA0300601)
文摘Superconducting quantum bits （qubits） and circuits are the leading candidate for the implementation of solid-state quantum computation. They have also been widely used in a variety of studies of quantum physics, atomic physics, quantum optics, and quantum simulation. In this article, we will present an overview of the basic principles of the superconducting qubits, including the phase, flux, charge, and transmon （Xmon） qubits, and the progress achieved so far concerning the improvements of the device design and quantum coherence property. Experimental studies in various research fields using the superconducting qubits and circuits will be briefly reviewed.
基金The project supported by the 973 Program under Grant No.2006CB921106National Natural Science Foundation of China under Grant Nos.10325521,60433050,60635040the SRFDP Program of Education Ministry of China under Grant No.20060003048
文摘The Hamiltonian of a superconducting charge qubit with a configuration of dc SQUID contains an interac-tion between the LC oscillator part and charge qubit.This interaction may leads to quantum state collapse and revivalwhich degrades the charge qubits and leads to serious decoherence.An analysis shows that the existing charge qubitparameters do not lead to this phenomenon,which is very good for the superconducting charge
基金supported by the National Natural Science Foundation of China (Grant Nos.12204139,U20A2076,12204138,12205069,11774076,and U21A20436)the Key-Area Research and Development Program of Guangdong Province (Grant No.2018B030326001).
文摘Motivated by recent realizations of two-dimensional(2D)superconducting-qubit lattices,we propose a protocol to simulate Hofstadter butterfly with synthetic gauge fields in superconducting circuits.Based on the existing 2D superconducting-qubit lattices,we construct a generalized Hofstadter model on zigzag lattices,which has a fractal energy spectrum similar to the original Hofstadter butterfly.By periodically modulating the resonant frequencies of qubits,we engineer a synthetic gauge field to mimic the generalized Hofstadter Hamiltonian.A spectroscopic method is used to demonstrate the Hofstadter butterfly from the time evolutions of experimental observables.We numerically simulate the dynamics of the system with realistic parameters,and the results show a butterfly spectrum clearly.Our proposal provides a promising way to realize the Hofstadter butterfly on the latest 2D superconducting-qubit lattices and will stimulate the quantum simulation of novel properties induced by magnetic fields in superconducting circuits.
基金supported by the National Basic Research Program of China(Grant No.2015CB921004)the National Key Research and Development Program of China(Grant Nos.2019YFA0308602,and 2016YFA0301700)+3 种基金the National Natural Science Foundation of China(Grant Nos.11934010,and 11775129)the Fundamental Research Funds for the Central Universities in Chinathe Anhui Initiative in Quantum Information Technologies(Grant No.AHY080000)the funding support from Tencent Corporation。
文摘Geometric phases are only dependent on evolution paths but independent of evolution details so that they possess some intrinsic noise-resilience features. Based on different geometric phases, various quantum gates have been proposed, such as nonadiabatic geometric gates based on nonadiabatic Abelian geometric phases and nonadiabatic holonomic gates based on nonadiabatic nonAbelian geometric phases. Up to now, nonadiabatic holonomic one-qubit gates have been experimentally demonstrated with superconducting transmons, where the three lowest levels are all utilized in operation. However, the second excited state of transmons has a relatively short coherence time, which results in a decreased fidelity of quantum gates. Here, we experimentally realize Abelian-geometric-phase-based nonadiabatic geometric one-qubit gates with a superconducting Xmon qubit. The realization is performed on the two lowest levels of an Xmon qubit and thus avoids the influence from the short coherence time of the second excited state. The experimental result indicates that the average fidelities of single-qubit gates can be up to 99.6% and 99.7% characterized by quantum process tomography and randomized benchmarking.
