Fighting decoherence in a continuous two-qubit odd or even parity measurement with a closed-loop setup

TL;DR

This paper proposes a closed-loop measurement setup for two-qubit parity detection that significantly reduces decoherence, improving quantum state fidelity in cavity-based atomic systems.

Contribution

It introduces a repeated interaction scheme with a probe light to suppress decoherence during parity measurements, a novel approach compared to traditional sequential methods.

Findings

Repeated probe interactions reduce decoherence rates.

Performance is comparable for resonant and nonresonant interactions.

Enhanced measurement fidelity within parity subspaces.

Abstract

A parity measurement on two qubits, each consisting of a single atom in a cavity, can be realized by measuring the phase shift of a probe beam, which interacts sequentially with the two qubits, but imperfections lead to decoherence within the subspaces of a given parity. We demonstrate that a different setup, where the probe light interacts repeatedly with the qubits, can reduce the rate of decoherence within the odd or the even parity subspace significantly. We consider both the case of a resonant and the case of a nonresonant light-atom interaction and find that the performance is comparable if the parameters are chosen appropriately.