Asymptotic security of discrete-modulation protocols for continuous-variable quantum key distribution

Eneet Kaur, Saikat Guha, Mark M. Wilde

Research output: Contribution to journalArticlepeer-review

Abstract

We consider discrete-modulation protocols for continuous-variable quantum key distribution (CV-QKD) that employ a modulation constellation consisting of a finite number of coherent states and that use a homodyne- or a heterodyne-detection receiver. We establish a security proof for collective attacks in the asymptotic regime, and we provide a formula for an achievable secret-key rate. Previous works established security proofs for discrete-modulation CV-QKD protocols that use two or three coherent states. The main constituents of our approach include approximating a complex, isotropic Gaussian probability distribution by a finite-size Gauss-Hermite constellation, applying entropic continuity bounds, and leveraging previous security proofs for Gaussian-modulation protocols. As an application of our method, we calculate secret-key rates achievable over a lossy thermal bosonic channel. We show that the rates for discrete-modulation protocols approach the rates achieved by a Gaussian-modulation protocol as the constellation size is increased. For pure-loss channels, our results indicate that in the high-loss regime and for sufficiently large constellation size, the achievable key rates scale optimally, i.e., proportional to the channel's transmissivity.

Original languageEnglish (US)
Article number012412
JournalPhysical Review A
Volume103
Issue number1
DOIs
StatePublished - Jan 15 2021

ASJC Scopus subject areas

  • Atomic and Molecular Physics, and Optics

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