Department of Physics and Astronomy, Institute for Quantum Computing, University of Waterloo, Waterloo, Ontario, Canada N2L3G1.
Nat Commun. 2016 May 20;7:11712. doi: 10.1038/ncomms11712.
Quantum key distribution (QKD) allows for communication with security guaranteed by quantum theory. The main theoretical problem in QKD is to calculate the secret key rate for a given protocol. Analytical formulas are known for protocols with symmetries, since symmetry simplifies the analysis. However, experimental imperfections break symmetries, hence the effect of imperfections on key rates is difficult to estimate. Furthermore, it is an interesting question whether (intentionally) asymmetric protocols could outperform symmetric ones. Here we develop a robust numerical approach for calculating the key rate for arbitrary discrete-variable QKD protocols. Ultimately this will allow researchers to study 'unstructured' protocols, that is, those that lack symmetry. Our approach relies on transforming the key rate calculation to the dual optimization problem, which markedly reduces the number of parameters and hence the calculation time. We illustrate our method by investigating some unstructured protocols for which the key rate was previously unknown.
量子密钥分发（QKD）允许通过量子理论保证的安全性进行通信。QKD 的主要理论问题是为给定协议计算密钥速率。对于具有对称性的协议，已知分析公式，因为对称性简化了分析。但是，实验不完美会破坏对称性，因此难以估计不完美对密钥速率的影响。此外，一个有趣的问题是（有意）不对称协议是否可以胜过对称协议。在这里，我们开发了一种用于计算任意离散变量 QKD 协议密钥速率的稳健数值方法。最终，这将允许研究人员研究“非结构化”协议，即那些缺乏对称性的协议。我们的方法依赖于将密钥速率计算转换为对偶优化问题，这显著减少了参数的数量，从而减少了计算时间。我们通过研究以前未知密钥速率的一些非结构化协议来说明我们的方法。
