空间链路量子无密钥保密与量子密钥分发
Quantum Keyless Privacy vs. Quantum Key Distribution for Space Links
摘要：
我们研究卫星和地面站之间空间链路的信息理论安全。量子密钥分发（QKD）是信息理论安全通信的一种成熟方法，它使窃听者能够不受量子物理定律的限制地访问信道和技术资源。但空间链路的量子密钥分配极具挑战性，实现的密钥速率极低，白天操作是不可能的。然而，由于轨道力学的限制，在自由空间中窃听信道而不被注意似乎很复杂。如果我们也排除窃听者在发射器和接收器周围的给定区域中的存在，我们可以保证他只能访问光信号的一小部分。在这种情况下，基于窃听信道模型的量子无密钥私有（直接）通信是提供信息理论安全的有效替代方案。与QKD一样，我们假设合法用户受到最先进技术的限制，而潜在的窃听者只受到物理定律的限制：物理测量（Helstrom探测器）和量子电动力学（Holevo束缚）。尽管如此，我们证明了信息理论的安全通信速率（积极的无密钥私人容量）在一个经典的量子窃听信道使用开关键控的相干态。我们提出了数值结果的设置相当于最近的实验与Micius卫星，并比较它们的基本限制的密钥速率的量子密钥分发。我们获得了更高的速率与QKD的禁区小于13米的低地球轨道（LEO）卫星相比。此外，我们表明，窃听信道量子无密钥隐私是不太敏感的噪声和信号动态和白天的操作是可能的。
英文摘要：
We study information theoretical security for space links between a satellite and a ground-station. Quantum key distribution (QKD) is a well established method for information theoretical secure communication, giving the eavesdropper unlimited access to the channel and technological resources only limited by the laws of quantum physics. But QKD for space links is extremely challenging, the achieved key rates are extremely low, and day-time operating impossible. However, eavesdropping on a channel in free-space without being noticed seems complicated, given the constraints imposed by orbital mechanics. If we also exclude eavesdropper's presence in a given area around the emitter and receiver, we can guarantee that he has only access to a fraction of the optical signal. In this setting, quantum keyless private (direct) communication based on the wiretap channel model is a valid alternative to provide information theoretical security. Like for QKD, we assume the legitimate users to be limited by state-of-the-art technology, while the potential eavesdropper is only limited by physical laws: physical measurement (Helstrom detector) and quantum electrodynamics (Holevo bound). Nevertheless, we demonstrate information theoretical secure communication rates (positive keyless private capacity) over a classical-quantum wiretap channel using on-off-keying of coherent states. We present numerical results for a setting equivalent to the recent experiments with the Micius satellite and compare them to the fundamental limit for the secret key rate of QKD. We obtain much higher rates compared with QKD with exclusion area of less than 13 meters for Low Earth Orbit (LEO) satellites. Moreover, we show that the wiretap channel quantum keyless privacy is much less sensitive to noise and signal dynamics and daytime operation is possible.
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