Heralded state preparation in a superconducting qubit

TL;DR

This paper demonstrates high-fidelity, nondestructive readout and heralded state preparation in a superconducting flux qubit, significantly improving initialization fidelity and enabling fast qubit reset without system modifications.

Contribution

It introduces a heralded state preparation method that enhances qubit initialization fidelity and offers a simple reset protocol in superconducting qubits.

Findings

Readout fidelity of 93.9% achieved

Heralding suppresses thermal population errors

Potential for fast, parameter-free qubit reset

Abstract

We demonstrate high-fidelity, quantum nondemolition, single-shot readout of a superconducting flux qubit in which the pointer state distributions can be resolved to below one part in 1000. In the weak excitation regime, continuous measurement permits the use of heralding to ensure initialization to a fiducial state, such as the ground state. This procedure boosts readout fidelity to 93.9% by suppressing errors due to spurious thermal population. Furthermore, heralding potentially enables a simple, fast qubit reset protocol without changing the system parameters to induce Purcell relaxation.