报告时间：10月23日下午4点 

报告地点：近代物理系210会议室

报告人：耶鲁大学 Gangqiang Liu postdoctor researcher

报告题目：Understanding gain saturation of Josephson Parametric Converter (JPC)

报告摘要：Microwave parametric amplifiers based on Josephson junctions have become a key component of many quantum information experiments. One key limitation which has not been well predicted by theory is the gain saturation behavior which determines its ability to process large amplitude signals. The typical explanation for this behavior in phase-preserving amplifiers based on three-wave mixing is pump depletion, in which the consumption of pump photons to produce amplification results in a reduction in gain. In this talk, however, I will present our recent numerical and experimental studies which show that the fourth-order Kerr nonlinearities inherent in the Josephson junctions are the dominant factor of gain saturation in the Josephson Parametric Converter (JPC). I will also present our ongoing efforts to eliminate these higher order nonlinearities through Hamiltonian engineering and novel device designs.

报告人简介：Dr. Gangqiang Liu earned his B.S. degree from Wuhan University in 2008, and his Ph.D. degree from the University of Pittsburgh in 2015. He subsequently stayed in Pittsburgh as a postdoctoral researcher for additional 3 years. In Oct. 2018, Dr. Liu started his new position in the Devoret group in Yale University. His research primarily focuses on superconducting circuits and polariton Bose-Einstein condensation. Dr. Liu has published numerous scientific articles in PNAS, Nature Physics, PRX and PRL etc.