Discrete-phase-randomized coherent state source and its application in quantum key distribution

TL;DR

This paper provides a rigorous security proof for quantum key distribution using discrete-phase-randomized coherent states, demonstrating near-equivalence to continuous randomization with significantly less randomness required.

Contribution

It introduces a security proof for QKD with discrete-phase randomization, reducing the randomness needed compared to continuous phase randomization.

Findings

Discrete-phase randomization closely approximates continuous case with about 10 phases.

Only 4 bits of randomness are needed for discrete-phase randomization.

Security performance remains robust with discrete-phase sources.

Abstract

Coherent state photon sources are widely used in quantum information processing. In many applications, such as quantum key distribution (QKD), a coherent state is functioned as a mixture of Fock states by assuming its phase is continuously randomized. In practice, such a crucial assumption is often not satisfied and, therefore, the security of existing QKD experiments is not guaranteed. To bridge this gap, we provide a rigorous security proof of QKD with discrete-phase-randomized coherent state sources. Our results show that the performance of the discrete-phase randomization case is close to its continuous counterpart with only a small number (say, 10) of discrete phases. Comparing to the conventional continuous phase randomization case, where an infinite amount of random bits are required, our result shows that only a small amount (say, 4 bits) of randomness is needed.