title: Initialization by measurement of a superconducting quantum bit circuit.
abstract: We demonstrate initialization by joint measurement of two transmon qubits in 3D circuit quantum electrodynamics. Homodyne detection of cavity transmission is enhanced by Josephson parametric amplification to discriminate the two-qubit ground state from single-qubit excitations nondestructively and with 98.1% fidelity. Measurement and postselection of a steady-state mixture with 4.7% residual excitation per qubit achieve 98.8% fidelity to the ground state, thus outperforming passive initialization.
authors.affiliation: Kavli Institute of Nanoscience, Delft University of Technology, The Netherlands.
authors.forename: D
authors.initials: D
authors.lastname: Ristè
authors.forename: J G
authors.initials: JG
authors.lastname: van Leeuwen
authors.forename: H-S
authors.initials: HS
authors.lastname: Ku
authors.forename: K W
authors.initials: KW
authors.lastname: Lehnert
authors.forename: L
authors.initials: L
authors.lastname: DiCarlo