Quick detection of transmittance changes in optical channel is crucial for secure communication. We demonstrate that pre-shared entanglement using two-mode squeezed vacuum states significantly reduces detection latency compared to classical and entanglement-augmented coherent-state probes. The change detection latency is inversely proportional to the quantum relative entropy (QRE), which goes to infinity in the absence of thermal noise, suggesting idealized instantaneous detection. However, in realistic scenarios, we show that QRE scales logarithmically with the inverse of the thermal noise mean photon number. We propose a receiver that achieves this scaling and quantify its performance gains over existing methods. Additionally, we explore the fundamental trade-off between communication capacity and change detection latency, highlighting how pre-shared entanglement enhances both.

翻译：快速检测光信道透射率变化对安全通信至关重要。我们证明，相较于经典探测方案和纠缠增强型相干态探测方案，采用双模压缩真空态预共享纠缠可显著降低检测延迟。变化检测延迟与量子相对熵成反比，在无热噪声的理想情况下量子相对熵趋于无穷大，这意味着可实现理想化的瞬时检测。然而在实际场景中，我们证明量子相对熵与热噪声平均光子数倒数的对数呈比例关系。我们提出一种可实现该比例关系的接收机方案，并量化其相对于现有方法的性能增益。此外，我们深入探讨了通信容量与变化检测延迟之间的基本权衡关系，揭示了预共享纠缠如何同时提升这两方面性能。