Security of the BB84 protocol with passive biased basis choice by the receiver

TL;DR

This paper provides a comprehensive security proof for the BB84 quantum key distribution protocol with a passive biased basis choice at the receiver, demonstrating its practical viability and negligible performance difference from active basis choice over typical distances.

Contribution

It offers the first fully analytical security proof for passive basis choice in BB84 with threshold detectors, extending security analysis to more realistic implementations.

Findings

Security proof applicable to coherent attacks

Negligible key rate difference between passive and active basis choices

Practical simulations confirm protocol robustness over long distances

Abstract

The Bennett-Brassard 1984 protocol (BB84 protocol) is one of the simplest protocols for implementing quantum key distribution (QKD). In the protocol, the sender and the receiver iteratively choose one of two complementary measurement bases. Regarding the basis choice by the receiver, a passive setup has been adopted in a number of its implementations including satellite QKD and time-bin encoding one. However, conventional theoretical techniques to prove the security of BB84 protocol are not applicable if the receiver chooses his measurement basis passively, rather than actively, with a biased probability, followed by the measurement with threshold detectors. Here we present a fully analytical security proof against coherent attacks for such a decoy-state BB84 protocol with receiver's passive basis choice and measurement with threshold detectors. The numerical simulations under practical situations show that the difference in secure key rate between the active and the passive implementations of the protocol is negligible except for long communication distances.