We theoretically study the quantum nondemolition measurements of a flux qubit coupled to a noisy superconduct- ing quantum interference device （SQUID）. The obtained analytical results indicate that the measurement p...We theoretically study the quantum nondemolition measurements of a flux qubit coupled to a noisy superconduct- ing quantum interference device （SQUID）. The obtained analytical results indicate that the measurement probability is frequency-dependent in a short time scale and has a close relationship with the measurement-induced dephasing. Furthermore, when the detuning between the driven and bare resonator equals the coupling strength, we can obtain the maximum measurement rate that is determined by the character of the noise in the SQUID. Finally, we analysed the mixed effect caused by coupling between the non-diagonal term and the external variable. It is found that the initial information of the qubit is destroyed due to quantum tunneling between the qubit states.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
基金Project supported by the National Natural Science Foundation of China (Grant No.10725415)the State Key Program for Basic Research of China (Grant No.2006CB921801)
文摘We theoretically study the quantum nondemolition measurements of a flux qubit coupled to a noisy superconduct- ing quantum interference device （SQUID）. The obtained analytical results indicate that the measurement probability is frequency-dependent in a short time scale and has a close relationship with the measurement-induced dephasing. Furthermore, when the detuning between the driven and bare resonator equals the coupling strength, we can obtain the maximum measurement rate that is determined by the character of the noise in the SQUID. Finally, we analysed the mixed effect caused by coupling between the non-diagonal term and the external variable. It is found that the initial information of the qubit is destroyed due to quantum tunneling between the qubit states.
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.
