Characterization of barrier-tunable radio-frequency-SQUID for Maxwell’s demon experiment**Project supported by the National Natural Science Foundation of China (Grant No. 11653001), the National Basic Research Program of China (Grant No. 2011CBA00304), the Tsinghua University Initiative Scientific Research Program, China (Grant No. 20131089314), and the Zhejiang Tianjingsheng Foundation, China, for Student Assistantships (Gang Li and Hao Li).

Abstract

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-AlOx/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.