Error threshold in active steering protocols for few-qubit systems

TL;DR

This paper investigates active steering protocols for weakly measured qubits under amplitude and phase noise, identifying a sharp error threshold that determines successful autonomous state stabilization.

Contribution

It introduces a numerical analysis of error thresholds in active steering for qubits, highlighting a phase transition between error-correcting and damping regimes.

Findings

A sharp error threshold separates successful stabilization from failure.

The purity gap closes at the threshold.

Numerical simulations for one and two qubits demonstrate the phenomenon.

Abstract

We study active steering protocols for weakly measured qubits in the presence of error channels due to amplitude and phase noise. If the error rate is sufficiently small, the protocol approaches and stabilizes a predesignated pure target state with high fidelity and high purity, and thus implements autonomous state stabilization. We present numerical simulation results for one and two qubits, taking Andreev qubit circuits as example. As function of the error rate, a sharp threshold separates an error-correcting weak-damping regime from a strong-damping regime where the target state cannot be reached anymore. At the threshold, the purity gap closes.