发表机构
Jeju National University; Yonsei University（济州国立大学; 延世大学）
机构由 AI 辅助整理，请以论文原文为准。AI 中文总结
本文提出在光纤中嵌入固定泡利旋转序列以无源抑制偏振漂移，建立了误差界，并在50公里光纤模拟中将平均QBER从6.11%降至0.224%，密钥率提升约2.5倍，为偏振编码QKD提供低开销的稳定方案。
AI 中文摘要
偏振量子比特为基于光纤的量子通信提供了一条直接途径，然而承载它们的纤芯也会通过不受控的双折射扰乱其参考系。主动补偿通常依赖于监测和反馈，这引发了一个自然的问题：链路本身能否在相干偏振漂移到达接收器之前将其抑制？我们证明，在足够相关的幺正漂移区域内，这是可以实现的。我们的核心思想是沿光纤嵌入一个固定的泡利旋转循环序列，将传播距离转化为一个空间翻转框架。该方法不是估计并反转未知变换，而是通过序列反复反转其主导作用。我们针对与两段式回波兼容的恒定生成元建立了精确重聚焦，证明了四帧泡利单元可消除任何无迹准静态生成元的主导贡献，并对平滑变化双折射的残余误差进行了界定。随后，我们将这些保证与可操作的BB84量联系起来，包括测得的量子比特误码率（QBER）、由此产生的密钥率份额以及插入损耗。在具有空间相关双折射的50公里光纤模拟中，一种代表性设计在器件间距为1.25公里时将平均QBER从6.11%降至0.224%。假设每器件透射率t=0.997，这将每发射脉冲的渐近密钥率提高了约2.5倍。对于该参数集，测试扫描中的最佳设计并非最密集的一种：误差抑制和光学损耗形成了一个有限的工作窗口。这些结果为无源偏振稳定提供了一种考虑损耗的设计原则，并为偏振编码QKD网络中的主动跟踪提出了一种低开销的补充方案。
英文摘要
Polarization qubits offer a direct route to fiber-based quantum communication, yet the fiber that carries them also scrambles their reference frame through uncontrolled birefringence. Active compensation commonly relies on monitoring and feedback, raising a natural question: can the link itself suppress coherent polarization drift before it reaches the receiver? We show that it can within a regime of sufficiently correlated unitary drift. Our central idea is to embed a fixed cyclic sequence of Pauli rotations along the fiber, turning propagation distance into a spatial toggling frame. Rather than estimating and inverting the unknown transformation, the sequence repeatedly reverses its leading action. We establish exact refocusing for constant generators compatible with a two-segment echo, show that a four-frame Pauli cell cancels the leading contribution of any traceless quasi-static generator, and bound the residual error for smoothly varying birefringence. We then connect these guarantees to operational BB84 quantities, including measured QBERs, the resulting secret fraction, and insertion loss. In simulations of a 50 km fiber with spatially correlated birefringence, a representative design reduces the mean QBER from 6.11% to 0.224% at a device spacing of 1.25 km. With an assumed per-device transmission of t = 0.997, this raises the asymptotic key rate per launched pulse by a factor of approximately 2.5. For this parameter set, the best design in the tested scan is not the densest one: error suppression and optical loss create a finite operating window. These results provide a loss-aware design principle for passive polarization stabilization and suggest a low-overhead complement to active tracking in polarization-encoded QKD networks.
