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arXiv:2512.01229 · EPJ Quantum Technology

Passive Polarization Stabilization for Practical and Robust Entanglement Distribution

Jin-Woo Kim, Minchul Kim, Jiho Park, Chunju Youn

quant-phSubmitted Dec 1, 2025• Announced Dec 2, 2025• 0 citations

v1 · Dec 1, 2025 v2 · Jun 19, 2026

Abstract

Quantum entanglement is a key resource in quantum information science, playing an essential role in quantum key distribution (QKD), quantum networks, and distributed quantum computing. However, practical applications require techniques capable of reliably distributing entanglement under lossy and noisy conditions. In this work, we demonstrate that a simple configuration using two polarization-maintaining fibers (PMFs) arranged in a cross-axis alignment enables stable distribution of entangled photon pairs without the need for real-time polarization compensation. To support this, we performed quantum information modeling and fidelity simulations for the cross-aligned PMF pair, and experimentally compared the entanglement preservation and interference fringe stability in setups based on standard single-mode fibers (SMFs) and PMFs. The experimental results show that the PMF-based configuration achieves an average visibility of 0.867 and an error propagation of 0.023 under unstable conditions, whereas the SMF setup exhibits a significantly lower stability with an average visibility of 0.444 and an error propagation of 0.167 under the same conditions. These results indicate that the cross-aligned PMF pair allows robust entanglement transmission without complex active compensation devices, suggesting its suitability for reliable quantum state distribution in long-distance quantum communication, drone-based QKD, and multi-user quantum networks.

Comments: 17 pages, 4 figures

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we experimentally demonstrate the distribution of polarization-entangled photons over a 62-km, partially-aerial fiber between the National Institute of Standards and Technology and the University of Maryland. With active polarization compensation applied to the fiber link, we observed a channel fidelity above 98%. Over the stabilized fiber link, we distributed approximately 1200 pairs of polarization-entangled photons per second over a course of 24 hours, with an average CHSH S-parameter value of 2.39 and a link up-time of 92.8% for entanglement distribution.

Entanglement distribution through optical fibers is essential for quantum communication networks; however, fiber transmission can alter photon polarization and modify the observed correlations of polarization-entangled states, necessitating polarization compensation to recover the desired entangled state in the measurement basis. Here, we experimentally evaluate two passive polarization compensation techniques: a free-space Quarter-Half-Quarter (QHQ) waveplate configuration and an in-fiber three-paddle Fiber Polarization Controller (FPC). The polarization transformation along each downconverted-photon path is independently compensated through a systematic path-by-path optimization procedure. Using both techniques, we recover high-quality polarization correlations and entanglement, with visibilities exceeding

93\%

in three mutually unbiased bases and fidelities above

94.5\%

. The results demonstrate comparable restoration using free-space waveplate-based and fiber-based control, establishing a systematic framework for laboratory and short-reach quantum communication links.

Distributing quantum entanglement over telecommunication fiber is a fundamental task in metropolitan-scale quantum networks, enabling advanced applications such as quantum-secured communication, quantum sensing, and distributed quantum computing. Although polarization entanglement is relatively easy to generate and manipulate, its distribution across deployed fibers is challenging because of the time-varying polarization transformations imposed by the fiber, which must be actively stabilized. In this work, we experimentally demonstrate the distribution of polarization-entangled photons over a 62 km, partially aerial fiber between the National Institute of Standards and Technology and the University of Maryland. With polarization stabilization applied to the fiber, we achieved a photon pair rate of approximately 1500s −1 and observed a time-averaged CHSH inequality parameter of S =2.34±0.37. During a continuous 24 h experiment, time-multiplexed polarization compensation sessions only cost 7.2% of the total link operation time, leaving an entanglement distribution uptime of 92.8%. Our results demonstrate the feasibility of distributing polarization-entangled photons over challenging fiber conditions, which is an important step toward the practical deployment of quantum networks.

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