Quantum computing and condensed matter physics with microwave photons

Fast Reset and Suppressing Spontaneous Emission of a Superconducting Qubit

M. D. Reed, B. R. Johnson, A. A. Houck, L. DiCarlo, J. M. Chow, D. I. Schuster, L. Frunzio, R. J. Schoelkopf

Spontaneous emission through a coupled cavity can be a significant decay channel for qubits in circuit QED. We present a new circuit design that effectively eliminates spontaneous emission due to the Purcell effect while maintaining strong coupling to a low Q cavity. Excellent agreement over a wide range in frequency is found between measured qubit relaxation times and the predictions of a circuit model. Using fast (nanosecond time-scale) flux biasing of the qubit, we demonstrate in-situ control of qubit lifetime over a factor of 50. We realize qubit reset with 99.9% fidelity in 120 ns.