Effect of different coupling modes on the high-frequency response of YBCO microwave SQUIDs

摘要

The effect of microwave and dc magnetic fields on the unloaded quality factor and the resonant frequency of two differently coupled hysteretic 3 GHz microwave SQUIDs was investigated. The SQUID loops are integrated into and solely inductively coupled to the superconducting resonator, respectively. The dissipative and the reactive response are analyzed in terms of a phenomenological model by Silver and Zimmerman. The temperature dependencies of the threshold field for microwave induced quantum transitions and of the coupling strength between SQUID ring and resonator are discussed. Conditions for optimized operation are deduced for both samples. The results indicate that it is possible to reduce the coupling coefficient, k$+2$/, by a suitable loop design while maintaining, at a reduced temperature, a sufficiently large dc field induced variation of the microwave losses (transfer function).