A Slow-Time Receiver Interface for Turbulent Free-Space Quantum Polarization Links

TL;DR

This paper introduces a slow-time receiver interface for turbulent free-space quantum polarization links, capturing temporal variations caused by atmospheric turbulence to improve receiver characterization.

Contribution

It extends static models to the temporal domain, modeling slow-time stochastic processes to generate a dynamic receiver interface for quantum links.

Findings

Polarization remains near-ideal with depolarization around 10^{-3}

Effective coherence stays close to unity in weak turbulence

Detection branch shows stronger fluctuations and longer correlation time

Abstract

Atmospheric turbulence makes free-space quantum polarization links intrinsically time varying, whereas receiver-side reduced interfaces are often treated as static. This paper develops a slow-time receiver interface by extending an aperture-conditioned static model to the temporal domain. The receiver-plane phase field, beam-centroid displacement, and scintillation are modeled as hidden slow-time stochastic processes, from which the reduced interface is generated at each instant. A leading-order closure maps coarse-grained phase roughness to an effective polarization-mixing variance while preserving the inherited local polarization-channel family. Aperture conditioning then yields time-dependent effective depolarization, coherence, and detection descriptors. In a representative weak-turbulence case, the polarization branch remains close to the near-ideal regime, with effective depolarization on the order of \(10^{-3}\) and effective coherence close to unity, whereas the detection branch exhibits visibly stronger fluctuations and a longer correlation time. These results show that a single static receiver-side parameterization is insufficient to characterize the temporal behavior of turbulent free-space quantum links. The resulting interface is intended for receiver-side characterization of time-varying quantum links, with MDI-QKD as one representative downstream application.