Security of differential quadrature phase shift quantum key distribution

TL;DR

This paper proves the security of the differential quadrature phase shift (DQPS) quantum key distribution protocol, demonstrating it offers a higher secure key rate than the phase-encoded BB84 protocol, with practical advantages.

Contribution

It provides the first security proof for the DQPS protocol, showing it achieves an 8/3 times higher key rate than PE-BB84, and highlights its practical benefits.

Findings

Security of DQPS protocol is proven.

DQPS achieves 8/3 higher key rate than PE-BB84.

Protocol is compatible with threshold detectors.

Abstract

One of the simplest methods for implementing quantum key distribution over fiber-optic communication is the Bennett-Brassard 1984 protocol with phase encoding (PE-BB84 protocol), in which the sender uses phase modulation over double pulses from a laser and the receiver uses a passive delayed interferometer. Using essentially the same setup and by regarding a train of many pulses as a single block, one can carry out the so-called differential quadrature phase shift (DQPS) protocol, which is a variant of differential phase shift (DPS) protocols. Here we prove the security of the DQPS protocol based on an adaptation of proof techniques for the BB84 protocol, which inherits the advantages arising from the simplicity of the protocol, such as accommodating the use of threshold detectors and simple off-line calibration methods for the light source. We show that the secure key rate of the DQPS protocol in the proof is eight thirds as high as the rate of the PE-BB84 protocol.