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Near-maximal two-photon entanglement for quantum communications at 2.1 $\mu$m

Adetunmise C. Dada, Jędrzej Kaniewski, Corin B. E. Gawith, Martin P. J. Lavery, Robert H. Hadfield, Daniele Faccio, Matteo Clerici

Published Jun 18, 2021• 0 citations
OpenAlex

Abstract

Owing to a reduced solar background and low propagation losses in the atmosphere, the 2- to 2.5-$\mu$m waveband is a promising candidate for daylight quantum communication. This spectral region also offers low losses and low dispersion in hollow-core fibers and in silicon waveguides. We demonstrate for the first time the capability for entanglement-based quantum key distribution (QKD) at 2.1 $\mu$m, obtaining a positive secure-key rate (0.417 bits/pair, with a quantum bit error rate of 5.43%) using near-maximally entangled photon pairs in a proof-of-principle device-independent QKD scenario.

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Near-maximal two-photon entanglement for quantum communications at 2.1 μ\muμm
Owing to a reduced solar background and low propagation losses in the atmosphere, the 2- to 2.5-μ\muμm waveband is a promising candidate for daylight quantum communication. This spectral region also offers low losses and low dispersion in hollow-core fibers and in silicon waveguides. We demonstrate for the first time the capability for entanglement-based quantum key distribution (QKD) at 2.1 μ\muμm, obtaining a positive secure-key rate (0.417 bits/pair, with a quantum bit error rate of 5.43%) using near-maximally entangled photon pairs in a proof-of-principle device-independent QKD scenario.
The 2- to 2.5-$\ensuremath{\mu}$m waveband enjoys reduced solar background and low propagation losses in the atmosphere and hollow-core optical fibers. However, harnessing these advantages for optical quantum communications has proved challenging due to a lack of suitable quantum light sources and detectors. The authors demonstrate in this waveband a source of entangled photons that is suitable for generating secure keys for quantum key distribution, and provide device-independent certification of the entanglement. These results are promising for the future implementation of device-independent secure optical quantum communications in daylight.
We report the first entanglement-based quantum key distribution (QKD) experiment over a 100-km optical fiber. We used superconducting single photon detectors based on NbN nanowires that provide high-speed single photon detection for the 1.5-mum telecom band, an efficient entangled photon pair source that consists of a fiber coupled periodically poled lithium niobate waveguide and ultra low loss filters, and planar lightwave circuit Mach-Zehnder interferometers (MZIs) with ultra stable operation. These characteristics enabled us to perform an entanglement-based QKD experiment over a 100-km optical fiber. In the experiment, which lasted approximately 8 hours, we successfully generated a 16 kbit sifted key with a quantum bit error rate of 6.9 % at a rate of 0.59 bits per second, from which we were able to distill a 3.9 kbit secure key.
Quantum key distribution (QKD) has emerged as a promising technique for secure communication in the post-quantum era, offering information-theoretic security against eavesdroppers with unlimited computational power. While fiber-based and satellite QKD systems have demonstrated impressive distances and key rates, terrestrial free-space QKD, which shows potential for secure mobile and wireless payment applications, remains relatively under-investigated due to severe ambient light interference. Here, we present a QKD link operating in the ultraviolet-C (UV-C) region, which is, to the best of our knowledge, the first such example. This has the potential to leverage the “solar-blind” nature of the UV-C region and mitigate sunlight interference. By integrating high-speed AlGaN micro-LEDs with silicon photomultiplier (SiPM)-based single-photon detectors (SPDs), we achieve a secure key rate (SKR) exceeding 1 Mbit/s. Furthermore, we analyze the system’s robustness to ambient light and propose a strategy for full sunlight rejection. Our results establish UV-C as a promising spectral window for terrestrial free-space QKD, paving the way for QKD implementations in daylight conditions.
An energy-time entanglement-based dispersive optics quantum key distribution (DO-QKD) is demonstrated experimentally over optical fibers of 20 km. In the experiment, the telecom band energy-time entangled photon pairs are generated through spontaneous four-wave mixing in a silicon waveguide. The arrival time of photons is registered for key generation and security test. High-dimensional encoding in the arrival time of photons is used to increase the information per coincidence of photon pairs. The bin sifting process is optimized by a three-level structure, which significantly reduces the raw quantum bit error rate (QBER) due to timing jitters of detectors and electronics. A raw key generation rate of 151 kbps with a QBER of 4.95% is achieved, in a time bin encoding format with 4 bits per coincidence. This experiment shows that the entanglement-based DO-QKD can be implemented in an efficient and convenient way, which has great potential for quantum secure communication networks in the future.