Initial experimental results on a superconducting-qubit reset based on photon-assisted quasiparticle tunneling

TL;DR

This paper demonstrates a qubit reset method using photon-assisted quasiparticle tunneling via a quantum-circuit refrigerator, achieving rapid reset times and high ground-state probability in a superconducting transmon qubit.

Contribution

The study introduces a novel qubit reset technique employing a QCR with rapid control pulses, improving reset speed and fidelity compared to previous methods.

Findings

Achieved roughly 97% ground-state probability after reset.

Reset times as short as 80 ns with optimized control pulses.

Demonstrated controllable energy relaxation via photon-assisted tunneling.

Abstract

We present here our recent results on qubit reset scheme based on a quantum-circuit refrigerator (QCR). In particular, we use the photon-assisted quasiparticle tunneling through a superconductor--insulator--normal-metal--insulator--superconductor junction to controllably decrease the energy relaxation time of the qubit during the QCR operation. In our experiment, we use a transmon qubit with dispersive readout. The QCR is capacitively coupled to the qubit through its normal-metal island. We employ rapid, square-shaped QCR control voltage pulses with durations in the range of 2--350 ns and a variety of amplitudes to optimize the reset time and fidelity. Consequently, we reach a qubit ground-state probability of roughly 97% with 80-ns pulses starting from the first excited state. The qubit state probability is extracted from averaged readout signal, where the calibration is based of the Rabi oscillations, thus not distinguishing the residual thermal population of the qubit.