发表机构
Shahid Beheshti University（沙希德贝赫什提大学）
机构由 AI 辅助整理，请以论文原文为准。AI 中文总结
本研究证明矢量涡旋光束在自由空间量子密钥分发中具有固有湍流免疫性，可将量子比特误码率从42.0%降至4.8%，无需主动自适应光学。
AI 中文摘要
轨道角动量（OAM）复用提供了无限维离散希尔伯特空间，非常适合高容量自由空间量子密钥分发（QKD）。然而，携带拓扑电荷（$|\ell| \ge 1$）的纯标量空间模式在通过地面大气湍流传输时会遭受严重的退相干。湍流折射率涡旋会分裂高阶涡旋奇点，在相邻拓扑信道之间诱发灾难性的模式间串扰，并迅速将量子比特误码率（QBER）推高至远超与个体克隆攻击相关的无条件11%安全阈值。在此，我们证明混合偏振-OAM纠缠态（称为矢量涡旋光束，VVBs）能提供固有的、无需硬件的抗湍流扰动免疫性。由于地面空气的光学各向异性极小（$\Delta n < 10^{-9}$），折射率波动对称地耦合到正交圆偏振模式，表现为一个相同的共模标量相位屏，该相位屏在相对偏振相位自由度中相互抵消。通过在湍流强度从$D/r_0 = 0$到$3.0$的范围内，对模态场进行数值传播并穿过修正的功率谱相位屏，我们表明VVB编码协议将渐近QBER从42.0%抑制到4.8%，实现了约11.6倍的误差抑制因子，而无需主动自适应光学或变形镜。
英文摘要
Orbital angular momentum (OAM) multiplexing provides an infinite-dimensional discrete Hilbert space ideally suited for high-capacity free-space quantum key distribution (QKD). Nevertheless, pure scalar spatial modes carrying topological charge ($|\ell| \ge 1$) undergo severe decoherence when transmitted through terrestrial atmospheric turbulence. Turbulent refractive-index eddies split high-order vortex singularities, induce catastrophic intermodal crosstalk across adjacent topological channels, and rapidly drive the quantum bit error rate (QBER) well above the unconditional 11% security threshold associated with individual cloning attacks. Here, we demonstrate that hybrid polarization-OAM entangled states, known as vector vortex beams (VVBs), provide intrinsic, hardware-free immunity against turbulent perturbations. Because the optical anisotropy of terrestrial air is exceedingly small ($Δn < 10^{-9}$), refractive-index fluctuations couple symmetrically to orthogonal circular polarization modes as an identical common-mode scalar phase screen that cancels in the relative polarization-phase degree of freedom. By numerically propagating modal fields through modified power-spectral phase screens over turbulence strengths ranging from $D/r_0 = 0$ to $3.0$, we show that the VVB encoding protocol suppresses the asymptotic QBER from 42.0% to 4.8%, yielding an error-suppression factor of approximately 11.6 without requiring active adaptive optics or deformable mirrors.
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