title: Fluxon readout of a superconducting qubit.
abstract: An experiment demonstrating a link between classical single-flux quantum digital logic and a superconducting quantum circuit is reported. We implement coupling between a moving Josephson vortex (fluxon) and a flux qubit by reading out of a state of the flux qubit through a frequency shift of the fluxon oscillations in an annular Josephson junction. The energy spectrum of the flux qubit is measured using this technique. The implemented hybrid scheme opens an opportunity to readout quantum states of superconducting qubits with the classical fluxon logic circuits.
authors.affiliation: Physikalisches Institut and DFG-Center for Functional Nanostructures (CFN), Karlsruhe Institute of Technology, D-76131 Karlsruhe, Germany and National University of Science and Technology MISIS, Leninsky prospekt 4, Moscow 119049, Russia.
authors.forename: Kirill G
authors.initials: KG
authors.lastname: Fedorov
authors.affiliation: Physikalisches Institut and DFG-Center for Functional Nanostructures (CFN), Karlsruhe Institute of Technology, D-76131 Karlsruhe, Germany.
authors.forename: Anastasia V
authors.initials: AV
authors.lastname: Shcherbakova
authors.affiliation: Institute of Nanotechnology, Karlsruhe Institute of Technology, 76021 Karlsruhe, Germany.
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Wolf
authors.affiliation: Institute of Nanotechnology, Karlsruhe Institute of Technology, 76021 Karlsruhe, Germany.
authors.forename: Detlef
authors.initials: D
authors.lastname: Beckmann
authors.affiliation: Physikalisches Institut and DFG-Center for Functional Nanostructures (CFN), Karlsruhe Institute of Technology, D-76131 Karlsruhe, Germany and National University of Science and Technology MISIS, Leninsky prospekt 4, Moscow 119049, Russia and Russian Quantum Center, 100 Novaya Street, Skolkovo, Moscow region 143025, Russia.
authors.forename: Alexey V
authors.initials: AV
authors.lastname: Ustinov