Tunable Resonant and Nonresonant Interactions between a Phase Qubit and L C Resonator
Michael S. Allman, Jed D. Whittaker, Manuel A. Castellanos-Beltran, Katarina Cicak, F. da Silva, M. P. DeFeo, Florent Lecocq, Adam J. Sirois, John D. Teufel, José Aumentado, Raymond W. Simmonds · Physical Review Letters · 2014
We use a flux-biased radio frequency superconducting quantum interference device (rf SQUID) with an embedded flux-biased direct current SQUID to generate strong resonant and nonresonant tunable interactions between a phase qubit and a lumped-element resonator. The rf SQUID creates a tunable magnetic susceptibility between the qubit and resonator providing resonant coupling strengths from zero to near the ultrastrong coupling regime. By modulating the magnetic susceptibility, nonresonant parametric coupling achieves rates $>100\text{ }\mathrm{MHz}$. Nonlinearity of the magnetic susceptibility also leads to parametric coupling at the subharmonics of the qubit-resonator detuning.