High frequency coupling coefficient between the coplanar resonator and radio frequency SQUID

The coupling coefficient (k(2)) between the superconducting coplanar resona tor and the flip chip coupled washer radio frequency SQUID was calculated u sing computer simulation. The coplanar resonator is formed by two coplanar lines surrounding a flux: concentrator,vith each line having a slit. For a 3 mm x 3 mm washer SQUID with a 100 mu m x 100 pm loop coupled to a coplana r resonator with the slits on opposite sides, we estimated k(2)=7.1x10(-3). However, if the same SQUID is coupled to a coplanar resonator with paralle l slits and with a short circuit at the 90 degrees position with respect to the opening slit, k(2) of only 0.5x10(-3) is obtained, which indicates tha t the k(2) is strongly dependent on the resonator layout. The simulation al so shows that k(2) is dependent on the SQUID washer size and the separation distance between the washer SQUID and the coplanar resonator.