Finite-key security of passive quantum key distribution

TL;DR

This paper establishes finite-key security bounds for a fully passive decoy-state BB84 quantum key distribution protocol, demonstrating its practical viability with comparable secret key rates to active systems.

Contribution

It provides the first finite-key security analysis for a fully passive QKD protocol, showing its performance is close to active approaches.

Findings

Secret key rate nearly matches perfect parameter estimation limits

Passive QKD is practical with high secret key rates

Security bounds are rigorously established for passive systems

Abstract

The passive approach to quantum key distribution (QKD) consists of eliminating all optical modulators and random number generators from QKD systems, in so reaching an enhanced simplicity, immunity to modulator side channels, and potentially higher repetition rates. In this work, we provide finite-key security bounds for a fully passive decoy-state BB84 protocol, considering a passive QKD source recently presented. With our analysis, the attainable secret key rate is comparable to that of the perfect parameter estimation limit, in fact differing from the key rate of the active approach by less than one order of magnitude. This demonstrates the practicality of fully passive QKD solutions.