Security analysis of passive measurement-device-independent continuous-variable quantum key distribution with almost no public communication

We perform security analysis of a passive measurement-device-independent (MDI) continuous-variable quantum key distribution (CVQKD) protocol with almost no public communication. In the passive MDI-CVQKD protocol, the quantum states are prepared passively by using thermal sources without Gaussian modulations at Alice's and Bob's sides. With this technique, Alice and Bob can precisely prepare quantum states to match the high transmission rate in MDI-CVQKD system at the corresponding speed. Here, both asymptotic regime and finite-size regime are considered. In asymptotic case, we derive the security bounds for the protocol against collective attacks, while in finite-size case we show a new conceptual development of passive MDI-CVQKD, namely the final secret key generation can be performed by using almost all raw keys instead of sacrificing part of raw keys for parameter estimation, and thus the improvement performance of passive MDI-CVQKD protocol can be achieved in finite-size scenario.