In situ quantum verification of polarization-stabilized optical channels

TL;DR

This paper presents a novel in situ quantum benchmarking method that combines classical polarization stabilization with quantum process tomography to better characterize and validate optical channels in quantum networks.

Contribution

It introduces a new approach that augments classical polarization tracking with quantum light for comprehensive channel noise analysis and validation.

Findings

Successfully implemented in a local-area quantum network.

Reconstructed quantum maps validated classical compensation effectiveness.

Exposed noise sources not captured by classical stabilization.

Abstract

The active stabilization of polarization channels is a task of growing importance as quantum networks move to deployed demonstrations over existing fiber infrastructure. However, the uniquely strict requirements for high-fidelity qubit transmission complicate the extent to which classical solutions may apply to future quantum networks, particularly in terms of recognizing noise sources present in low-flux, nonunitary channels. Here we introduce a novel in situ benchmarking approach that augments a classical polarization tracking system, limited to unitary correction, with simultaneously transmitted quantum light for ancilla-assisted process tomography of the full quantum map. Implemented in a local-area quantum network, our method uses the reconstructed map both to validate the classical compensation and to expose noise sources it fails to capture. A sliding measurement window that continuously updates the estimated quantum process further increases sensitivity to rapid channel fluctuations. Our results should unlock new opportunities for in situ channel characterization in quantum-classical coexistence networks.