Floodlight Quantum Key Distribution: Demonstrating a New Framework for High-Rate Secure Communication

TL;DR

Floodlight QKD introduces a high-rate, secure quantum communication framework that significantly outperforms existing systems in secret-key rate and efficiency over metropolitan distances using a novel broadband and two-way protocol.

Contribution

This paper presents the first experimental demonstration of Floodlight QKD, a new high-rate QKD protocol utilizing broadband homodyne detection and photon injection for enhanced security and performance.

Findings

Achieved 55 Mbit/s secret-key rate over 50 km fiber

Demonstrated ~500-fold improvement in secret-key efficiency

Achieved ~50-fold increase in secret-key rate compared to prior systems

Abstract

Floodlight quantum key distribution (FL-QKD) is a radically different QKD paradigm that can achieve Gbit/s secret-key rates over metropolitan area distances without multiplexing [Phys. Rev. A 94, 012322 (2016)]. It is a two-way protocol that transmits many photons per bit duration and employs a high-gain optical amplifier, neither of which can be utilized by existing QKD protocols to mitigate channel loss. FL-QKD uses an optical bandwidth that is substantially larger than the modulation rate and performs decoding with a unique broadband homodyne receiver. Essential to FL-QKD is Alice's injection of photons from a photon-pair source--in addition to the light used for key generation--into the light she sends to Bob. This injection enables Alice and Bob to quantify Eve's intrusion and thus secure FL-QKD against collective attacks. Our proof-of-concept experiment included 10 dB propagation loss--equivalent to 50 km of low-loss fiber--and achieved a 55 Mbit/s secret-key rate (SKR) for a 100 Mbit/s modulation rate, as compared to the state-of-the-art system's 1 Mbit/s SKR for a 1 Gbit/s modulation rate [Opt. Express 21, 24550-24565 (2013)], representing ~500-fold and ~50-fold improvements in secret-key efficiency (SKE) (bits per channel use) and SKR (bits per second), respectively.