Passive polarization-encoded BB84 protocol using a heralded single-photon source

TL;DR

This paper demonstrates a passive polarization-encoded BB84 quantum key distribution protocol using a heralded single-photon source, simplifying design, enhancing security, and achieving practical secure key rates.

Contribution

It introduces a passive encoding scheme with a heralded single-photon source that reduces complexity and security vulnerabilities compared to traditional active methods.

Findings

Achieved a quantum bit error rate of 7%.

Secure key rate of 5 kbps.

Confirmed low multi-photon emission probability with $g^{2}(0)=0.0408\

Abstract

The BB84 quantum key distribution protocol set the foundation for achieving secure quantum communication. Since its inception, significant advancements have aimed to overcome experimental challenges and enhance security. In this paper, we report the implementation of a passive polarization-encoded BB84 protocol using a heralded single-photon source. By passively and randomly encoding polarization states with beam splitters and half-wave plates, the setup avoids active modulation, simplifying design and enhancing security against side-channel attacks. The heralded single-photon source ensures a low probability of multi-photon emissions, eliminating the need for decoy states and mitigating photon number splitting vulnerabilities. The quality of the single-photon source is certified by measuring the second-order correlation function at zero delay, $g^{2}(0)=0.0408\pm0.0008$, confirming a very low probability of multi-photon events. Compared to conventional BB84 or BBM92 protocols, our protocol provides optimized resource trade-offs, with fewer detectors (compared to BBM92) and no reliance on external quantum random number generators (compared to typical BB84) to drive Alice's encoding scheme. Our implementation achieved a quantum bit error rate of 7% and a secure key rate of 5 kbps. These results underscore the practical, secure, and resource-efficient framework our protocol offers for scalable quantum communication technologies.