title: Superconducting qubit with Purcell protection and tunable coupling.
abstract: We present a superconducting qubit for the circuit quantum electrodynamics architecture that has a tunable qubit-resonator coupling strength g. This coupling can be tuned from zero to values that are comparable with other superconducting qubits. At g = 0, the qubit is in a decoherence-free subspace with respect to spontaneous emission induced by the Purcell effect. Furthermore, we show that in this decoherence-free subspace, the state of the qubit can still be measured by either a dispersive shift on the resonance frequency of the resonator or by a cycling-type measurement.
authors.affiliation: Department of Applied Mathematics, Institute for Quantum Computing, University of Waterloo, Waterloo, Ontario, Canada N2L 3G1.
authors.forename: J M
authors.initials: JM
authors.lastname: Gambetta
authors.forename: A A
authors.initials: AA
authors.lastname: Houck
authors.forename: Alexandre
authors.initials: A
authors.lastname: Blais