Dispersive readout of a flux qubit using a microstrip SQUID amplifier

ORAL

Abstract

Dispersive techniques for the readout of superconducting qubits offer the possibility of high repetition-rate quantum non-demolition measurement by avoiding dissipation close to the qubit. We demonstrate a dispersive readout scheme in which a three junction aluminum flux qubit is inductively coupled to a 1-2 GHz oscillator formed by a capacitively shunted SQUID. The SQUID in this readout oscillator acts as a nonlinear, flux-dependent inductor so that the oscillator resonance frequency depends on the state of the qubit. Readout is performed by microwave reflectometry; the reflected signal is amplified using a microstrip SQUID amplifier (MSA) with a noise temperature of a few hundred millikelvin. This noise temperature is an order of magnitude lower than that of the HEMT (high electron mobility transistor) amplifier that follows the MSA. We report measurements in both the linear (weak drive) and the bistable (strong drive) oscillator regimes.

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Authors

  • E.M. Hoskinson

    QNL, UC Berkeley, Quantum Nanoelectronics Laboratory and Dept. of Physics, UC Berkeley

  • D. H. Slichter

    Quantum Nanoelectronics Lab, UC Berkeley, Quantum Nanoelectronics Laboratory, Dept. of Physics, UC Berkeley

  • J.E. Johnson

    Dept. of Physics, UC Berkeley

  • C. Macklin

    Quantum Nanoelectronics Laboratory, Dept. of Physics, UC Berkeley

  • Ofer Naaman

    Quantum Nanoelectronics Laboratory, Dept. of Physics, UC Berkeley, Quantum Nanoelectronics Laboratory, Department of Physics, University of California, Berkeley

  • John Clarke

    University of California at Berkeley and Lawrence Berkeley National Lab, University of California, Berkeley, UC Berkeley, Dept. of Physics, UC Berkeley, Department of Physics, University of California Berkeley and Materials Sciences Division, Lawrence Berkeley National Laboratory, Department of Physics, University of California, Berkeley, CA 94720

  • Irfan Siddiqi

    University of California, Berkeley, QNL, UC Berkeley, Quantum Nanoelectronics Laboratory, Dept. of Physics, UC Berkeley, Quantum Nanoelectronics Laboratory, Department of Physics, University of California, Berkeley