Fig. 1: Composability in continuous-variable quantum key distribution (CVQKD) with coherent states.
From: Practical continuous-variable quantum key distribution with composable security
Alice and Bob obtain quantum correlations over the quantum channel by means of modulation (MOD) and local oscillator (LO) aided homodyne/heterodyne detection (HD) to prepare and measure, respectively, optical coherent states. After going through the remaining steps of the protocol that involve the authenticated channel, they obtain correlated bitstreams sA and sB, respectively. Certain criteria associated with correctness, robustness, and secrecy of the protocol must be satisfied, for the application to assure composable security7,10. For instance, ϵ-correctness implies that Alice and Bob possess the same symmetric key s( = sA = sB) except with a probability ϵcor that bounds the probability of them having non-identical keys (Pr[sA ≠ sB]≤ϵcor). This key can be used for encrypting a message and decrypting the corresponding ciphertext across the communication channel. Dashed lines with arrows indicate classical communication across the channel and local operations. Eve is assumed to control all the channels. Further details of our CVQKD protocol implementation are presented in later sections of this article.
