Measurements of quasiparticle tunneling rate in a superconducting transmon qubit

A practical quantum computer requires qubits with long coherence times in order to perform many quantum gates. For a superconducting qubit, non-equilibrium quasiparticle tunneling is one possible source of decoherence. Spectroscopy measurements of a superconducting transmon qubit can be used to set a bound on the quasiparticle tunneling rate. When operated in the low $E_J$/$E_C$ regime, the transmon qubit transition frequency switches between two well-resolved branches due to quasiparticle tunneling. A selective $\pi$ pulse applied to one of these two branches can excite the qubit only if the qubit is at that frequency. Thus by repeatedly applying $\pi$ pulses to interrogate the qubit state, the quasiparticle dynamics can be studied. We will present our results on the quasiparticle tunneling rate in a transmon qubit.