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Frontiers in Optics

Towards Polarization-encoded QKD with room-temperature telecom single-photon source over 32.5 km fiber

Xingjian Zhang, Zhang Haoran, Weibo Gao, Alexander Ling

Published Jan 1, 2024• 0 citations
Publisher

Abstract

We report a polarization-encoded BB84 experiment using O-band single photons from a GaN emitter, over a 32.5km fiber spool. A Quantum Bit Error Rate (QBER) of 6.4% and a secure key rate of 47.3 bps are obtained.
DOI
10.1364/fio.2024.jw5a.12

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Quantum key distribution (QKD) with deterministic single photon sources has been demonstrated over intercity fiber and free-space channels. The previous implementations relied mainly on polarization encoding schemes, which are susceptible to birefringence, polarization-mode dispersion and polarization-dependent loss in practical fiber networks. In contrast, time-bin encoding offers inherent robustness and has been widely adopted in mature QKD systems using weak coherent laser pulses. However, its feasibility in conjunction with a deterministic single-photon source has not yet been experimentally demonstrated. In this work, we construct a time-bin encoded QKD system employing a high-brightness quantum dot (QD) single-photon source operating at telecom wavelength. Our proof-of-concept experiment successfully demonstrates the possibility of secure key distribution over fiber link of 120 km, while maintaining extraordinary long-term stability over 6 h of continuous operation, that is highest secure key rate among the time-bin QKDs based on single-photon sources. This work provides the first experimental validation of integrating a QD single-photon source with time-bin encoding in a telecom-band QKD system. This development signifies a substantial advancement in the establishment of a robust and scalable QKD network based on solid-state single-photon technology.
Single-photon sources (SPSs) hold the potential to enhance the performance of quantum key distribution (QKD). QKD systems using SPS often require cryogenic cooling, while recent QKD attempts using SPS operating at room temperature have failed to achieve long-distance transmission due to the SPS not operating at telecommunication wavelength. In this work, we have successfully demonstrated QKD using a room-temperature SPS at telecommunication wavelength. The SPS used in this work is based on point defects hosted by gallium nitride (GaN\mathrm{Ga}\mathrm{N}GaN) thin films grown on sapphire substrates. We employed a time-bin and phase-encoding scheme to perform the BB84 and reference-frame-independent QKD protocols over a 33-km fiber spool, achieving a secure key rate of $7.58\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}7}$ per pulse. Moreover, we also implemented a metropolitan QKD experiment over a 30-km deployed fiber, achieving a secure key rate of $6.06\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}8}$ per pulse. These results broaden the prospects for future use of SPS in commercial QKD applications.
A method for exceeding the 100 km barrier for quantum key distribution (QKD) over a standard telecom fiber was described. The system was based upon a time division Mach-Zender interferometer using phase modulation. The single photon detector was optimized by minimizing the contribution to the intrinsic error rate of detector dark count noise and stray photons. It was observed that a quantum bit error ratio (QBER) of 8.9% was achieved for a 122 km link, allowing a secure shared key to be formed after error correction and privacy amplification.