Coherent State Quantum Key Distribution with Multi Letter Phase-Shift Keying

TL;DR

This paper introduces a quantum key distribution protocol using discrete phase modulation of coherent states, enabling secure communication with flexible modulation schemes and optimized parameters for enhanced security.

Contribution

It proposes a novel QKD protocol with multi-letter phase-shift keying, allowing basis-independent measurement and security optimization through parameter tuning.

Findings

Protocol supports various modulation schemes from binary to continuous.

Security can be improved by optimal parameter selection.

No active basis choice required for decoding.

Abstract

We present a protocol for quantum key distribution using discrete modulation of coherent states of light. Information is encoded in the variable phase of coherent states which can be chosen from a regular discrete set ranging from binary to continuous modulation, similar to phase-shift-keying in classical communication. Information is decoded by simultaneous homodyne measurement of both quadratures and requires no active choice of basis. The protocol utilizes either direct or reverse reconciliation, both with and without postselection. We analyze the security of the protocol and show how to enhance it by the optimal choice of all variable parameters of the quantum signal.