Optimal gauge for the multimode Rabi model in circuit QED
Marco Roth, Fabian Hassler, David P. DiVincenzo · Physical Review Research · 2019
Projecting an anharmonic oscillator coupled to a resonator onto a two-level subspace yields a Rabi model. It has been noted that the validity of this truncation is gauge dependent. The authors identify a prescription for finding the optimal gauge in a multiple-resonator scenario.