A fully passive transmitter for decoy-state quantum key distribution

TL;DR

This paper presents a simplified passive quantum key distribution transmitter that enhances security and operational frequency by eliminating active modulators, with a novel security analysis for decoy-state QKD.

Contribution

It introduces a simplified passive QKD transmitter with improved security analysis and distinct encoding and decoy-state generation methods.

Findings

Simplified the passive QKD transmitter design.

Developed a tighter security analysis surpassing previous assumptions.

Achieved potential for higher frequency operation without active modulators.

Abstract

A passive quantum key distribution (QKD) transmitter generates the quantum states prescribed by a QKD protocol at random, combining a fixed quantum mechanism and a post-selection step. By avoiding the use of active optical modulators externally driven by random number generators, passive QKD transmitters offer immunity to modulator side channels and potentially enable higher frequencies of operation. Recently, the first linear optics setup suitable for passive decoy-state QKD has been proposed. In this work, we simplify the prototype and adopt sharply different approaches for BB84 polarization encoding and decoy-state generation. On top of it, we elaborate a tight custom-made security analysis surpassing an unnecessary assumption and a post-selection step that are central to the former proposal.