Bebrov Georgi
Telecommunications Department, Technical University of Varna, 9010, Varna, Bulgaria.
Sci Rep. 2022 Sep 13;12(1):15377. doi: 10.1038/s41598-022-15247-x.
A great challenge in the field of quantum cryptography is the design and implementation of optimal quantum key distribution (QKD) scheme. An optimal scheme in terms of security is the so-called relativistic quantum key distribution; it ensures the security of the system by using both quantum phenomena and relativity. However, the existing relativistic schemes have not demonstrated optimality in terms of efficiency and rate (including secret key rate). Here we report two point-to-point relativistic quantum key distribution schemes implemented with weak coherent pulses. Both schemes rely on high-dimensional quantum systems (phase and polarization encodings are utilized for establishing key bits). One of the proposed schemes is a system comprised of two sequentially connected interferometers, as the first (interferometer) controls the behavior of the second one. The other proposed scheme represents a setup of a classic relativistic QKD, but with slight modification. Both of the proposed schemes are characterized with high secret key rate. The latter scheme has the highest secret key rate of all the relativistic QKD protocols. However, the values for the secret key rate are relevant for distances of up to 150 km. The former scheme has lower secret key rate, but longer operating distances (the work could operate at distances of up to 320 km). Those values of rate are obtained without disturbing the security. Secret-key-rate comparison between distinct models is reported. The proposed relativistic models are compared to twin-field QKD protocols. Furthermore, the work proposes a metric for evaluating the optimality of a QKD. It is defined as a ratio between the secret key rate (at a given distance) and the amount of quantum resources (qubits) used in the QKD of concern. It is shown that one of the proposed schemes in this article is the most optimal relativistic key distribution and more optimal than the original twin-field. It is also verified that the proposed schemes excels the original twin-field in terms of secret key rate, but for short distances.
量子密码学领域的一个重大挑战是设计和实现最优量子密钥分发（QKD）方案。就安全性而言的最优方案是所谓的相对论量子密钥分发；它通过利用量子现象和相对论来确保系统的安全性。然而，现有的相对论方案在效率和速率（包括密钥率）方面尚未证明其最优性。在此，我们报告了两种使用弱相干脉冲实现的点对点相对论量子密钥分发方案。这两种方案都依赖于高维量子系统（利用相位和偏振编码来建立密钥位）。所提出的方案之一是由两个顺序连接的干涉仪组成的系统，第一个（干涉仪）控制第二个干涉仪的行为。另一个提出的方案代表了一种经典相对论QKD的设置，但有轻微修改。所提出的两种方案都具有高密钥率的特点。后一种方案在所有相对论QKD协议中具有最高的密钥率。然而，密钥率的值适用于长达150公里的距离。前一种方案的密钥率较低，但工作距离更长（该工作可在长达320公里的距离上运行）。这些速率值是在不影响安全性的情况下获得的。报告了不同模型之间的密钥率比较。将所提出的相对论模型与双场QKD协议进行了比较。此外，该工作提出了一种用于评估QKD最优性的度量。它被定义为（在给定距离下的）密钥率与所关注的QKD中使用的量子资源（量子比特）量之间的比率。结果表明，本文中提出的方案之一是最优化的相对论密钥分发，并且比原始双场更优。还验证了所提出的方案在密钥率方面优于原始双场，但仅适用于短距离。
