We develop a fabrication process for the superconducting phase qubits in which Josephson junctions for both the qubit and superconducting quantum interference device（SQUID） detector are prepared by shadow evaporatio...We develop a fabrication process for the superconducting phase qubits in which Josephson junctions for both the qubit and superconducting quantum interference device（SQUID） detector are prepared by shadow evaporation with a suspended bridge. Al junctions with areas as small as 0.05 μm^2 are fabricated for the qubit, in which the number of the decoherencecausing two-level systems（TLS） residing in the tunnel barrier and proportional to the junction area are greatly reduced. The measured energy spectrum shows no avoided crossing arising from coherent TLS in the experimentally reachable flux bias range of the phase qubit, which demonstrates the energy relaxation time T1 and dephasing time Tφ on the order of 100 ns and 50 ns, respectively. We discuss several possible origins of decoherence from incoherent or weakly-coupled coherent TLS and further improvements of the qubit performance.展开更多
We report a fabrication process and characterization of the Josephson parametric amplifier(JPA) for the single-shot quantum state measurement of superconducting multiqubit system. The device is prepared using Nb film ...We report a fabrication process and characterization of the Josephson parametric amplifier(JPA) for the single-shot quantum state measurement of superconducting multiqubit system. The device is prepared using Nb film as its base layer,which is convenient in the sample patterning process like e-beam lithography and film etching. Our results show that the JPA has a bandwidth up to 600 MHz with gain above 15 dB and noise temperature approaching the quantum limit. The qubit state differentiation measurements demonstrate the signal-to-noise ratio around 3 and the readout fidelity above 97%and 91% for the ground and first-excited states, respectively.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
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
基金supported by the National Basic Research Program of China(Grant Nos.2014CB921202,2015CB921104,and 2016YFA0300601)the National Natural Science Foundation of China(Grant Nos.91321208 and 11674380)
文摘We develop a fabrication process for the superconducting phase qubits in which Josephson junctions for both the qubit and superconducting quantum interference device（SQUID） detector are prepared by shadow evaporation with a suspended bridge. Al junctions with areas as small as 0.05 μm^2 are fabricated for the qubit, in which the number of the decoherencecausing two-level systems（TLS） residing in the tunnel barrier and proportional to the junction area are greatly reduced. The measured energy spectrum shows no avoided crossing arising from coherent TLS in the experimentally reachable flux bias range of the phase qubit, which demonstrates the energy relaxation time T1 and dephasing time Tφ on the order of 100 ns and 50 ns, respectively. We discuss several possible origins of decoherence from incoherent or weakly-coupled coherent TLS and further improvements of the qubit performance.
基金Project supported by the Science Funds from the Ministry of Science and Technology of China(Grant Nos.2015CB921104 and 2016YFA0300601)the National Natural Science Foundation of China(Grant Nos.11674380 and 11874063)+1 种基金the Strategic Priority Research Program of the Chinese Academy of Sciences(Grant Nos.XDB07010300 and XDB28000000)the Key Research and Development Program of Guangdong Province,China(Grant No.2018B030326001)
文摘We report a fabrication process and characterization of the Josephson parametric amplifier(JPA) for the single-shot quantum state measurement of superconducting multiqubit system. The device is prepared using Nb film as its base layer,which is convenient in the sample patterning process like e-beam lithography and film etching. Our results show that the JPA has a bandwidth up to 600 MHz with gain above 15 dB and noise temperature approaching the quantum limit. The qubit state differentiation measurements demonstrate the signal-to-noise ratio around 3 and the readout fidelity above 97%and 91% for the ground and first-excited states, respectively.
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.
