Abstract:
Twin-field quantum key distribution (TF-QKD) relies on first-order interference between coherent optical fields combined at an intermediate station, which requires simultaneous phase and polarization stabilization. We present a Sagnac-like interferometric architecture arranged in a hybrid star–bus network topology that enables any-to-any connectivity while providing passive stabilization of phase and polarization fluctuations for multiple wavelengths. The proposed configuration, which integrates Faraday mirrors in a Plug-and-Play scheme, operates without active feedback. Experimental results in a 110 km-long installed fiber link between the cities of Linköping and Nyköping, Sweden, show 99.2% visibility maintained over 14 hours of continuous operation with 0.33% standard deviation. The main limitation of this configuration — Rayleigh backscattering — was circumvented by time filtering.