Fast and Unconditional All-Microwave Reset of a Superconducting Qubit

Active qubit reset is a key operation in many quantum algorithms, and particularly in quantum error correction. Here, we experimentally demonstrate a reset scheme for a three-level transmon artificial atom coupled to a large bandwidth resonator. The reset protocol uses a microwave-induced interaction between the vertical bar f, 0 > and vertical bar g, 1 > states of the coupled transmon-resonator system, with vertical bar g > and vertical bar f > denoting the ground and second excited states of the transmon, and vertical bar 0 > and vertical bar 1 > the photon Fock states of the resonator. We characterize the reset process and demonstrate reinitialization of the transmon-resonator system to its ground state in less than 500 ns and with 0.2% residual excitation. Our protocol is of practical interest as it has no additional architectural requirements beyond those needed for fast and efficient single-shot readout of transmons, and does not require feedback.