用于光子量子存储器和量子中继器的有限能量GKP-QPC架构
Finite-energy GKP-QPC architectures for photonic quantum memories and repeaters
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中文总结 AI 辅助
该研究提出有限能量GKP-QPC级联架构，经实验验证其可降低量子存储器的压缩阈值、提升平均保真度比，还能大幅提高量子中继器的密钥率并扩展通信距离，为相关器件提供设计准则。
中文摘要 AI 辅助
光子量子网络需要能在有限能量玻色态、纯损耗光纤传输及明确资源核算条件下仍能发挥作用的纠错架构。基于此，我们研究一种级联架构：每个物理轨是经纯损耗光纤段传输的有限压缩Gottesman-Kitaev-Preskill（GKP，戈特斯曼-基塔夫-普雷斯基尔）量子比特，采用基于隐形传态的有限压缩辅助量子比特的GKP纠错进行修正，再通过外层量子奇偶校验码（QPC）解码。GKP层将连续零差校验子转换为有效的轨级泡利边际值，QPC层则抑制残留的量子比特级误差。对于本文所考虑的级联码族，我们发现零传输损耗下的有限压缩阈值为5.06 dB。在存储器场景中，QPC层将重复纠错变得有益的压缩阈值从纯GKP纠错的6.7 dB降至QPC(3,3)的5.2 dB和QPC(5,5)的4.3 dB，并在相关的中等噪声区域将平均保真度比提升了75%至90%。在中继器场景中，避免前置放大可在中等压缩下获得更大的秘密密钥率，但也会产生最优压缩，因为高度压缩的GKP峰值对损耗引起的向内位移敏感。资源归一化速率表明，QPC级联可将无中继器的PLOB基准提高几个数量级，并在短中继器间距下将通信范围扩展至约10^4 km（采用14 dB压缩）。不过，当每个基本链路损耗过高时，QPC级联会产生不利影响。这些结果为有限压缩GKP-QPC量子存储器和中继器提供了定量设计准则。
英文摘要
Photonic quantum networks require error-correction architectures that remain useful with finite-energy bosonic states, pure-loss fiber transmission, and explicit resource accounting. In this light, we study a concatenated architecture in which each physical rail is a finitely squeezed Gottesman--Kitaev--Preskill (GKP) qubit transmitted through a pure-loss fiber segment, corrected by teleportation-based GKP error correction with finitely squeezed ancillae, and decoded by an outer quantum parity code (QPC). The GKP layer converts continuous homodyne syndromes into effective rail-level Pauli marginals, while the QPC layer suppresses the residual qubit-level errors. For the concatenated code family considered here, we find a finite-squeezing threshold of $5.06\,\mathrm{dB}$ at zero propagation loss. In the memory setting, the QPC layer lowers the squeezing at which repeated error correction becomes beneficial from $6.7\,\mathrm{dB}$ for bare GKP correction to $5.2\,\mathrm{dB}$ for QPC$(3,3)$ and $4.3\,\mathrm{dB}$ for QPC$(5,5)$, and improves the average-fidelity ratio by up to $75$--$90\%$ in the relevant intermediate-noise regime. In the repeater setting, avoiding pre-amplification gives larger secret-key fractions at moderate squeezing, but also produces an optimal squeezing because highly squeezed GKP peaks become sensitive to loss-induced inward displacement. Resource-normalized rates show that QPC concatenation can exceed the repeaterless PLOB benchmark by orders of magnitude and extend the communication reach, at short repeater spacing, to distances of order $10^4$km with $14$dB squeezing. However, QPC concatenation becomes detrimental when each elementary hop is too lossy. These results provide quantitative design rules for finite-squeezing GKP--QPC quantum memories and repeaters.
