All-microwave leakage reduction units for quantum error correction with superconducting transmon qubits

TL;DR

This paper presents an all-microwave leakage reduction unit (LRU) for superconducting transmon qubits that significantly reduces leakage errors, improving quantum error correction performance with minimal impact on qubit states.

Contribution

The authors experimentally realize and extend a microwave-based LRU for transmons, achieving up to 99% leakage reduction and demonstrating its effectiveness in quantum error correction protocols.

Findings

Achieved up to 99% leakage reduction in 220 ns

Reduced leakage buildup to below 1% over 50 cycles

Demonstrated improved error detection in quantum error correction

Abstract

Minimizing leakage from computational states is a challenge when using many-level systems like superconducting quantum circuits as qubits. We realize and extend the quantum-hardware-efficient, all-microwave leakage reduction unit (LRU) for transmons in a circuit QED architecture proposed by Battistel et al. This LRU effectively reduces leakage in the second- and third-excited transmon states with up to $99\% $ efficacy in $220~\mathrm{ns}$, with minimum impact on the qubit subspace. As a first application in the context of quantum error correction, we demonstrate the ability of multiple simultaneous LRUs to reduce the error detection rate and to suppress leakage buildup within $1\%$ in data and ancilla qubits over 50 cycles of a weight-2 parity measurement.