This paper investigates the relationship between the speed of a quantum not gate and the asymmetry of the potential in an interactive system formed by a two-level RF-SQUID qubit and a classical microwave pulse. The RF...This paper investigates the relationship between the speed of a quantum not gate and the asymmetry of the potential in an interactive system formed by a two-level RF-SQUID qubit and a classical microwave pulse. The RFSQUID is characterized by an asymmetric double well potential which gives rise to diagonal matrix elements that describe the interaction of the SQUID with the microwave pulse. And the diagonal matrix elements account for the interaction of the microwave pulse with the SQUID. The results indicate that, when the angular frequency of the microwave field is chosen as near resonate with the transition （0） ←→ （1）, i.e. ω1 -ω0 ≈ ωm, （1） the gate speed is decided by three factors, the Rabi frequency, the difference of the diagonal matrix elements between the two levels, and the angular frequency of the applied microwave pulse ωm; （2） the gate speed descends when the asymmetry of the potential is considered.展开更多
We have observed the macroscopic resonant tunneling of magnetic flux between macroscopically distinct quantum states in a superconducting flux qubit. The dependences of the macroscopic resonant tunneling on the barrie...We have observed the macroscopic resonant tunneling of magnetic flux between macroscopically distinct quantum states in a superconducting flux qubit. The dependences of the macroscopic resonant tunneling on the barrier height of the potential well, the flux bias and the initial state are investigated. Detailed measurements of the tunneling rate as a function of the flux bias reveal the feature of the quantum noise in the superconducting flux qubit.展开更多
At an extremely low temperature of 20 inK, we measured the loop current in a tunable rf superconducting quantum interference device （SQUID） with a dc-SQUID. By adjusting the magnetic flux applied to the rf-SQUID lo...At an extremely low temperature of 20 inK, we measured the loop current in a tunable rf superconducting quantum interference device （SQUID） with a dc-SQUID. By adjusting the magnetic flux applied to the rf-SQUID loop （Фf） and the small dc-SQUID （Фfcjj）, respectively, the potential shape of the system can be fully controlled in situ. Variation in the transition step and overlap size in the switching current with a barrier flux bias are analyzed, from which we can obtain some relevant device parameters and build a model to explain the experimental phenomenon.展开更多
We propose a potential scheme of preparing Schrodinger-cat state of the cavity mode by placing an rfsuperconducting quantum interference device （rf-SQUID） in a single-mode microwave cavity. By properly adjusting the...We propose a potential scheme of preparing Schrodinger-cat state of the cavity mode by placing an rfsuperconducting quantum interference device （rf-SQUID） in a single-mode microwave cavity. By properly adjusting the detuning and the strength regarding the radiation fields, we show how to generate single-mode Schrodinger-cat state. Generalizing this method we discuss the generation of the engtangled coherent states. The experimental feasibility of our scheme is discussed under consideration of the cavity decay.展开更多
Nowadays, the high-critical-temperature radio frequency superconducting quantum interference device （high-Tc rf SQUID） is usually coupled to a dielectric resonator that is a standard 10× 10×1 mm^3 SrTiO3 ...Nowadays, the high-critical-temperature radio frequency superconducting quantum interference device （high-Tc rf SQUID） is usually coupled to a dielectric resonator that is a standard 10× 10×1 mm^3 SrTiO3 （STO） substrate with a YBa2Cu3O7-δ （YBCO） thin-film flux focuser deposited on it. Recently, we have simulated a dielectric resonator for the high-Tc rf SQUID by using the ANSOFT High Frequency Structure Simulator （ANSOFT HFSS）. We simulate the resonant frequency and the quality factor of our dielectric resonator when it is unloaded or matches a 50-Ω impedance. The simulation results are quite close to the practical measurements. Our study shows that ANSOFT HFSS is quite suitable for simulating the dielectric resonator used for the high-Tc rf SQUID. Therefore, we think the ANSOFT HFSS can be very helpful for investigating the characteristics of dielectric resonators for high-Tc rf SQUIDs.展开更多
We present the design, fabrication, and characterization of a barrier-tunable superconducting quantum interference device（SQUID） qubit for the study of Maxwell＇s demon experiment. In this work, a compound Josephson...We present the design, fabrication, and characterization of a barrier-tunable superconducting quantum interference device（SQUID） qubit for the study of Maxwell＇s demon experiment. In this work, a compound Josephson junction（CJJ）radio-frequency（RF）-SQUID qubit with an overdamped resistively shunted direct-current（DC）-SQUID magnetometer is used to continuously monitor the state of the qubit. The circuit is successfully fabricated with the standard Nb/Al-Al Ox/Nb trilayer process of our laboratory and characterized in a low noise measurement system, which is capable of measuring coherent dynamics of superconducting qubits, in an Oxford dilution refrigerator. All circuit parameters are determined accurately by fitting experimental data to theoretical analysis and simulation, which allows us to make a quantitative comparison between the results of the experiment and theory.展开更多
基金Project supported by the Science and Technology Research Foundation of the Education Department of Jiangxi Province,China(Grant No 200592)
文摘This paper investigates the relationship between the speed of a quantum not gate and the asymmetry of the potential in an interactive system formed by a two-level RF-SQUID qubit and a classical microwave pulse. The RFSQUID is characterized by an asymmetric double well potential which gives rise to diagonal matrix elements that describe the interaction of the SQUID with the microwave pulse. And the diagonal matrix elements account for the interaction of the microwave pulse with the SQUID. The results indicate that, when the angular frequency of the microwave field is chosen as near resonate with the transition （0） ←→ （1）, i.e. ω1 -ω0 ≈ ωm, （1） the gate speed is decided by three factors, the Rabi frequency, the difference of the diagonal matrix elements between the two levels, and the angular frequency of the applied microwave pulse ωm; （2） the gate speed descends when the asymmetry of the potential is considered.
基金Project supported by the New Century Excellent Talents in University,Chinathe National Natural Science Foundation of China(Grant Nos. 11074114 and 10874074)the National Basic Research Program of China (Grant No. 2011CBA00200)
文摘We have observed the macroscopic resonant tunneling of magnetic flux between macroscopically distinct quantum states in a superconducting flux qubit. The dependences of the macroscopic resonant tunneling on the barrier height of the potential well, the flux bias and the initial state are investigated. Detailed measurements of the tunneling rate as a function of the flux bias reveal the feature of the quantum noise in the superconducting flux qubit.
基金Project supported by the National Basic Research Program of China (Grant Nos. 2011CBA00107 and 2011CBA00202)the National Natural Science Foundation of China (Grant Nos. 61027008 and 11074114)
文摘At an extremely low temperature of 20 inK, we measured the loop current in a tunable rf superconducting quantum interference device （SQUID） with a dc-SQUID. By adjusting the magnetic flux applied to the rf-SQUID loop （Фf） and the small dc-SQUID （Фfcjj）, respectively, the potential shape of the system can be fully controlled in situ. Variation in the transition step and overlap size in the switching current with a barrier flux bias are analyzed, from which we can obtain some relevant device parameters and build a model to explain the experimental phenomenon.
基金National Natural Science Foundation of China under Grant Nos.10474118 and 6049028Scientific Fund for Distinguished Young Scholars of Hubei Province,and partly by the National Fundamental Research Program of China under Grant No.2005CB724502
文摘We propose a potential scheme of preparing Schrodinger-cat state of the cavity mode by placing an rfsuperconducting quantum interference device （rf-SQUID） in a single-mode microwave cavity. By properly adjusting the detuning and the strength regarding the radiation fields, we show how to generate single-mode Schrodinger-cat state. Generalizing this method we discuss the generation of the engtangled coherent states. The experimental feasibility of our scheme is discussed under consideration of the cavity decay.
基金Project supported by the National Basic Research Program of China (Grant No.2006CB601007)the National Natural Science Foundation of China (Grant No.10674006)+1 种基金the National High Technology Research and Development Program of China (Grant No.2007AA03Z238)the Foundation of the State Key Laboratory of Information Control Technology for Communication System,China (Grant No.9140C1304010803)
文摘Nowadays, the high-critical-temperature radio frequency superconducting quantum interference device （high-Tc rf SQUID） is usually coupled to a dielectric resonator that is a standard 10× 10×1 mm^3 SrTiO3 （STO） substrate with a YBa2Cu3O7-δ （YBCO） thin-film flux focuser deposited on it. Recently, we have simulated a dielectric resonator for the high-Tc rf SQUID by using the ANSOFT High Frequency Structure Simulator （ANSOFT HFSS）. We simulate the resonant frequency and the quality factor of our dielectric resonator when it is unloaded or matches a 50-Ω impedance. The simulation results are quite close to the practical measurements. Our study shows that ANSOFT HFSS is quite suitable for simulating the dielectric resonator used for the high-Tc rf SQUID. Therefore, we think the ANSOFT HFSS can be very helpful for investigating the characteristics of dielectric resonators for high-Tc rf SQUIDs.
基金supported by the National Natural Science Foundation of China(Grant No.11653001)the National Basic Research Program of China(Grant No.2011CBA00304)+1 种基金the Tsinghua University Initiative Scientific Research Program,China(Grant No.20131089314)the Zhejiang Tianjingsheng Foundation,China,for Student Assistantships(Gang Li and Hao Li)
文摘We present the design, fabrication, and characterization of a barrier-tunable superconducting quantum interference device（SQUID） qubit for the study of Maxwell＇s demon experiment. In this work, a compound Josephson junction（CJJ）radio-frequency（RF）-SQUID qubit with an overdamped resistively shunted direct-current（DC）-SQUID magnetometer is used to continuously monitor the state of the qubit. The circuit is successfully fabricated with the standard Nb/Al-Al Ox/Nb trilayer process of our laboratory and characterized in a low noise measurement system, which is capable of measuring coherent dynamics of superconducting qubits, in an Oxford dilution refrigerator. All circuit parameters are determined accurately by fitting experimental data to theoretical analysis and simulation, which allows us to make a quantitative comparison between the results of the experiment and theory.
