Qubit-Resonator Interactions Enabled by Driving

Qubit-Resonator Interactions Enabled by Driving

This paper develops a theory for multiphoton qubit-resonator interactions that are enhanced when the qubit is driven at specific frequencies. A key result is the realization of qubit-conditional squeezing of the resonator state when the qubit is driven at twice the resonator frequency. This qubit-conditional squeezing can be used to amplify displacements in the resonator, encode qubit states in the resonator, and perform quantum non-demolition measurements of the qubit state. The interactions can be tuned to arbitrary strengths using two-tone driving. A circuit QED implementation involving a transmon qubit coupled to a resonator via an asymmetric SQUID is proposed and shown to be robust against decoherence.