Abstract
Continuous-variable measurement-device-independent quantum key distribution (CV-MDI-QKD) allows remote parties to share information-theoretical secure keys while defending all the side-channel attacks on measurement devices. However, the secure transmission distance and the secret key rate are quite limited due to the high untrusted equivalent excess noise in the Gaussian modulation. More particularly, extremely high-efficiency homodyne detections are required for even non-zero secure transmission distances, which directly restrict its practical realization. Here, we propose a CV-MDI-QKD protocol by encoding the key information into matched discrete phases of two groups of coherent states, which decreases the required detection efficiency for ideally asymmetric cases, and makes it possible to practically achieve secure key distribution with current low-efficiency homodyne detections. Besides, a proof-of-principle experiment with a locally generated oscillator is implemented, which, for the first time, demonstrates the realizability of CV-MDI-QKD using all fiber-based devices. The discrete-modulated phase-matching method provides an alternative direction of an applicable quantum key distribution with practical security.
Highlights
Continuous-variable quantum key distribution (CV-QKD) [1–5] allows two remote authenticated users to establish a secure key through untrusted quantum channels, and authenticated classical channels, by using coherent detection
We propose a realizable CV-MDI-QKD scheme by encoding the key information into some discrete and matched specific phases, where the correlation between the legitimate parities can be established after Charlie publicly announces the results of the homodyne detections
The eavesdropping analysis is provided under a typical non-Gaussian attack, which is constructed by an SD receiver and a heralded noiseless linear amplifier (NLA), when combined with the BS and partial IR attacks
Summary
Continuous-variable quantum key distribution (CV-QKD) [1–5] allows two remote authenticated users to establish a secure key through untrusted quantum channels, and authenticated classical channels, by using coherent detection. In order to thoroughly eliminate the practical security vulnerabilities at the measurement side, the Gaussian-modulated coherent-state (GMCS) continuous-variable measurement-device-independent quantum key distribution (CV-MDI-QKD) protocols are proposed [23–26]. In these CV-MDI-QKD schemes, two legitimate parties, Alice and Bob, are both senders, and an untrusted third party, Charlie, is employed to perform Bell-State Measurement (BSM) and broadcast the outcomes to help to create the secret correlations between Alice and Bob. Despite the possibility that Charlie’s station can be fully tampered with, the legitimate parties can still extract the secure keys under optimal coherent attacks via insecure quantum channels. When comparing the conventional GMCS CV-MDI-QKD schemes, the proposed discrete-modulated phase-matching (DMPM) CV-MDI-QKD protocol can theoretically achieve secure key distribution with current low-efficiency detections for the ideally asymmetric case, against a typical and powerful non-Gaussian individual attack, which could reach the quantum limit of the discrimination of the discrete encoded quantum states. The experimental realizability of the proposed phase-matching scheme under realistic conditions is demonstrated
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