A security proof of continuous-variable QKD using three coherent states

Understand

We introduce a ternary quantum key distribution (QKD) protocol and asymptotic security proof based on three coherent states and homodyne detection.

• Previous work had considered the binary case of two coherent states and here we nontrivially extend this to three.
• Our motivation is to leverage the practical benefits of both discrete and continuous (Gaussian) encoding schemes creating a best-of-both-worlds approach; namely, the postprocessing of discrete encodings and the hardware benefits of continuous ones.
• We present a thorough and detailed security proof in the limit of infinite signal states which allows us to lower bound the secret key rate.