Probabilistic amplitude shaping for continuous-variable quantum key distribution with discrete modulation over a wiretap channel

TL;DR

This paper demonstrates that probabilistic amplitude shaping of discrete symbols can optimize channel capacity in continuous-variable quantum key distribution, even at higher powers, enhancing secure communication over wiretap channels.

Contribution

It introduces a novel probabilistic amplitude shaping protocol for CV-QKD that approximates optimal channel capacity with finite power constraints.

Findings

Shaping improves key generation rate at higher powers.

The protocol effectively approximates Gaussian distribution sampling.

Feasibility shown for wiretap channel scenarios.

Abstract

To achieve the maximum information transfer and face a possible eavesdropper, the samples transmitted in continuous-variable quantum key distribution (CV-QKD) protocols are to be drawn from a continuous Gaussian distribution. As a matter of fact, in practical implementations the transmitter has a finite (power) dynamics and the Gaussian sampling can be only approximated. This requires the quantum protocols to operate at small powers. In this paper, we show that a suitable probabilistic amplitude shaping of a finite set of symbols allows to approximate at will the optimal channel capacity also for increasing average powers. We investigate the feasibility of this approach in the framework of CV-QKD, propose a protocol employing discrete quadrature amplitude modulation assisted with probabilistic amplitude shaping, and we perform the key generation rate analysis assuming a wiretap channel and lossless homodyne detection.