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Conference on Lasers and Electro-Optics

Floodlight Quantum Key Distribution

Quntao Zhuang, Zheshen Zhang, Justin Dove, Franco N. C. Wong, Jeffrey H. Shapiro

Published Jan 1, 2016• 0 citations
Publisher

Abstract

We describe a quantum key distribution protocol that breaks the one-photon-per-bit barrier, is secure against the optimum collective Gaussian attack, and is capable of a 2 Gbps secret-key rate over a 50 km fiber link.
DOI
10.1364/cleo_qels.2016.fth3c.1

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Existing quantum key distribution protocols typically transmit at most one photon per bit, so that the no-cloning theorem ensures their security. As a result, their key rates suffer dramatically in long-distance transmission because of channel loss. We introduce floodlight quantum key distribution (FL-QKD), which breaks the one photon per bit barrier and overcomes loss by exploiting a huge number of optical modes per bit. FL-QKD is capable of 2 Gbps secret-key rates over a 50 km fiber link. Its security follows from employing less than one photon per mode and using photon-coincidence channel monitoring.
The channel loss incurred in long-distance transmission places a significant burden on quantum key distribution (QKD) systems: they must defeat a passive eavesdropper who detects all the light lost in the quantum channel and does so without disturbing the light that reaches the intended destination. The current QKD implementation with the highest long-distance secret-key rate meets this challenge by transmitting no more than one photon per bit [M. Lucamarini et al., Opt. Express 21, 24550 (2013)]. As a result, it cannot achieve the Gbps secret-key rate needed for one-time pad encryption of large data files unless an impractically large amount of multiplexing is employed. We introduce floodlight QKD (FL-QKD), which floods the quantum channel with a high number of photons per bit distributed over a much greater number of optical modes. FL-QKD offers security against the optimum frequency-domain collective attack by transmitting less than one photon per mode and using photon-coincidence channel monitoring, and it is completely immune to passive eavesdropping. More importantly, FL-QKD is capable of a 2-Gbps secret-key rate over a 50-km fiber link, without any multiplexing, using available equipment, i.e., no new technology need be developed. FL-QKD achieves this extraordinary secret-key rate by virtue of its unprecedented secret-key efficiency, in bits per channel use, which exceeds those of state-of-the-art systems by two orders of magnitude.
Floodlight quantum key distribution (FL-QKD) is a radically different QKD paradigm that can achieve gigabit-per-second secret-key rates over metropolitan area distances without multiplexing [Q. Zhuang et al., 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 [M. Lucamarini et al., Opt. Express 21, 24550 (2013)], representing $\ensuremath{\sim}500$-fold and $\ensuremath{\sim}50$-fold improvements in secret-key efficiency (bits per channel use) and SKR (bits per second), respectively.