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<p>Quantum two-way time transfer (Q-TWTT) is fundamentally limited by wavelength-dependent nonreciprocity between counter-propagating photons, which induces undesired time-offset drifts and compromises its long-term stability. To overcome this bottleneck, we propose and experimentally validate a superimposed Q-TWTT (SQ-TWTT) protocol. By shifting the transmission scheme from bidirectional single-photon exchange to concurrent streams of photon pairs, SQ-TWTT confers robust immunity to nonreciprocal delays. Comparative tests conducted over a 113 km fiber link revealed a fundamental divergence in performance. Whereas conventional Q-TWTT exhibited a time-offset drift that scaled proportionally with both the photon wavelength difference and the link dispersion, the SQ-TWTT protocol maintained negligible sensitivity to these nonreciprocal effects. Over a wavelength mismatch range from 0 to 4.64 nm, the time-offset in conventional Q-TWTT accumulated dramatically to (164.35 ± 2.65) ps. In stark contrast, SQ-TWTT sustained a negligible drift of (0.07 ± 1.94) ps over the same range. These results, in excellent agreement with theory, confirm that SQ-TWTT breaks the long-standing limitation of Q-TWTT and establishes a practical, high-precision solution for long-distance time synchronization in fiber-optic networks.</p>

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Overcoming wavelength-dependent nonreciprocity using superimposed quantum two-way time transfer

  • 期刊论文

  • 发表日期：

    2026年4月22日

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  • Zhiguang Xia,
  • Runai Quan,
  • Xiao Xiang,
  • Huibo Hong,
  • Bingke Shi,
  • Yuting Liu,
  • Tao Liu,
  • Mingtao Cao,
  • Ruifang Dong,
  • Shougang Zhang

摘要

Quantum two-way time transfer (Q-TWTT) is fundamentally limited by wavelength-dependent nonreciprocity between counter-propagating photons, which induces undesired time-offset drifts and compromises its long-term stability. To overcome this bottleneck, we propose and experimentally validate a superimposed Q-TWTT (SQ-TWTT) protocol. By shifting the transmission scheme from bidirectional single-photon exchange to concurrent streams of photon pairs, SQ-TWTT confers robust immunity to nonreciprocal delays. Comparative tests conducted over a 113 km fiber link revealed a fundamental divergence in performance. Whereas conventional Q-TWTT exhibited a time-offset drift that scaled proportionally with both the photon wavelength difference and the link dispersion, the SQ-TWTT protocol maintained negligible sensitivity to these nonreciprocal effects. Over a wavelength mismatch range from 0 to 4.64 nm, the time-offset in conventional Q-TWTT accumulated dramatically to (164.35 ± 2.65) ps. In stark contrast, SQ-TWTT sustained a negligible drift of (0.07 ± 1.94) ps over the same range. These results, in excellent agreement with theory, confirm that SQ-TWTT breaks the long-standing limitation of Q-TWTT and establishes a practical, high-precision solution for long-distance time synchronization in fiber-optic networks.