Pilot-reference-free continuous-variable quantum key distribution with efficient decoy-state analysis

TL;DR

This paper introduces a reference-free, time-bin-encoded continuous-variable quantum key distribution protocol that simplifies security analysis and enhances key rates by utilizing multi-photon components and decoy-state analysis.

Contribution

It presents a novel CV QKD protocol that removes the need for global references and enables efficient parameter estimation through decoy states and phase randomization.

Findings

Key rate increases by two orders of magnitude with multi-photon components.

Decoy-state analysis achieves tight parameter estimation.

Protocol performance is comparable to BB84 at short distances.

Abstract

Continuous-variable quantum key distribution (CV QKD) using optical coherent detectors is practically favorable due to its low implementation cost, flexibility of wavelength division multiplexing, and compatibility with standard coherent communication technologies. However, the security analysis and parameter estimation of CV QKD are complicated due to the infinite-dimensional latent Hilbert space. Also, the transmission of strong reference pulses undermines the security and complicates the experiments. In this work, we tackle these two problems by presenting a time-bin-encoding CV protocol with a simple phase-error-based security analysis valid under general coherent attacks. With the key encoded into the relative intensity between two optical modes, the need for global references is removed. Furthermore, phase randomization can be introduced to decouple the security analysis of different photon-number components. We can hence tag the photon number for each round, effectively estimate the associated privacy using a carefully designed coherent-detection method, and independently extract encryption keys from each component. Simulations manifest that the protocol using multi-photon components increases the key rate by two orders of magnitude compared to the one using only the single-photon component. Meanwhile, the protocol with four-intensity decoy analysis is sufficient to yield tight parameter estimation with a short-distance key-rate performance comparable to the best Bennett-Brassard-1984 implementation.