Superconducting non-linear resonator for non-destructive readout of a flux qubit

Abstract

We have investigated microwave response of a λ/4 superconducting coplanar waveguide resonator which is terminated by a DC-SQUID coupled with a flux qubit. The circuit is designed for non-destructive single-shot readout of a flux qubit based on dispersive interaction between the qubit and the resonator and switching between bistable states of the driven nonlinear resonator. A high-frequency (∼ 10 GHz) resonator is exploited for suppressing photon-number fluctuations which cause qubit dephasing even when the readout circuit is not activated. We observed bifurcation of the resonator in the nonlinear driving regime. In the linear regime, the degeneracy point of the qubit was detected as a shift of the resonant frequency.