Unconditional optimality of Gaussian attacks against continuous-variable QKD

摘要

A fully general approach to the security analysis of continuous-variablequantum key distribution (CV-QKD) is presented. Provided that the quantumchannel is estimated via the covariance matrix of the quadratures, Gaussianattacks are shown to be optimal against all eavesdropping strategies, includingcollective and coherent attacks. The proof is made strikingly simple bycombining a physical model of measurement, an entanglement-based description ofCV-QKD, and a recent powerful result on the extremality of Gaussian states[Phys. Rev. Lett. 96, 080502 (2006)].