Catch-Disperse-Release Readout for Superconducting Qubits*

We analyze a qubit readout scheme for superconducting qubits via controlled capture, dispersion, and release of a microwave field. A tunable coupler is used to decouple the microwave resonator from a transmission line during dispersive interaction with the qubit, thus circumventing the Purcell effect. We show that fast and high-fidelity qubit readout can be achieved for nonlinear dispersive qubit-resonator interaction and for sufficiently adiabatic tuning of the qubit frequency. Interestingly, the Jaynes-Cummings nonlinearity results in quadrature squeezing of the microwave field which leads to a significant decrease in measurement error. The effects of qubit anharmonicity and imperfect quantum efficiency of the microwave amplification on the measurement error are also discussed.