Passive leakage removal unit based on a disordered transmon array

TL;DR

This paper introduces a passive leakage removal method for superconducting qubits using a disordered transmon array, leveraging localization effects to enhance quantum error correction.

Contribution

It proposes a novel passive leakage removal unit based on disordered transmon arrays with feedback or dissipation, compatible with existing quantum processors.

Findings

Optimal measurement rates for leakage removal identified.

Leakage excitations propagate until removed at the last site.

Method is compatible with current superconducting qubit technology.

Abstract

Leakage out from the qubit subspace compromises standard quantum error correction protocols and is a challenge for practical quantum computing. We propose a passive leakage removal unit based on an array of coupled disordered transmons and last-site reset by feedback-measurement or dissipation. The transmons have parametric disorder both in frequency and anharmonicity such that the qubit subspace is protected by localization through energy level mismatch while the energy levels for leakage excitations are in resonance for maximized leakage mobility. Leakage excitations propagate through the idle transmons until reaching the last site with feedback-measurement or dissipation removing them. For removing leakage excitations, we find two optimal measurement rates, which are comprehensively understood through two distinct timescales between the propagation and disintegration of leakage excitations. Based only on an array of standard transmon devices, our approach is readily compatible with existing superconducting quantum processor designs under realistic conditions.