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Quantum Information and Computation

Feasibility study of free-Space quantum key distribution in the mid-infrared

Guilherme P. Temporão, H. Zibinden, Sébastien Tanzilli, Nicolas Gisin, Thierry Aellen, Marcella Giovannini, Jérôme Faist, Jean Pierre von der Weid

Published Jan 1, 2008• 31 citations
Publisher

Abstract

We report on a feasibility study of a free-space Quantum Key Distribution setup operating at a mid-infrared wavelength. Alice sends polarization-coded pseudo-single photons from a Quantum Cascade Laser at 4.6 $\mu$m to Bob, who uses a nonlinear crystal and a Silicon Avalanche Photodiode to perform the detection via Sum Frequency Generation. Theoretical predictions, based on a proof-of-principle experiment, show that, under certain foggy atmospheric conditions, the proposed system is barely affected, whereas other systems operating at standard near-infrared wavelengths would simply not work at all.

DOI
10.26421/qic8.1-2-1

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We report on a feasibility study of a free-space Quantum Key Distribution setup operating at a mid-infrared wavelength. Alice sends polarization-coded pseudo-single photons from a Quantum Cascade Laser at 4.6 μ\muμm to Bob, who uses a nonlinear crystal and a Silicon Avalanche Photodiode to perform the detection via Sum Frequency Generation. Theoretical predictions, based on a proof-of-principle experiment, show that, under certain foggy atmospheric conditions, the proposed system is barely affected, whereas other systems operating at standard near-infrared wavelengths would simply not work at all.
Abstract Satellite quantum key distribution technology has developed rapidly using near-infrared wavelengths and is expected to enable global quantum communication. However, link availability is still hampered by detrimental effects in the free-space channel, such as background noise from solar radiation and attenuation from turbulence and weather such as haze and fog. One potential mitigation technique is to move to the mid-infrared atmospheric transmission window (3–5 µ ms) where background noise and turbulence effects are significantly reduced. While mid-infrared quantum technology is not as well developed, advancements in mid-infrared entangled photon pair generation and nonlinear upconversion single-photon detectors could be poised to enable daytime satellite downlinks with increased reliability. This review compares the state of the art for quantum transmitters and receivers in the mid-infrared to the more established near-infrared technology. The goal is to identify gaps in transmitter and/or receiver technology in the mid-infrared, and to determine if the mid-infrared can offer significant advantages over the near infrared for quantum communication.
Free Space Optics (FSO) is a growing technology offering higher bandwidth with fast and cost-effective deployment compared to fiber technology. This work demonstrates private free-space communication with quantum cascade lasers (QCLs). The secret message is encoded into a chaotic waveform so that the information is hard for an eavesdropper to extract [1]. Chaos-based transmissions in FSO are fundamentally restricted by atmospheric phenomena (e.g., turbulence, fog or scattering). Thus, the operating wavelength is a key parameter that has to be chosen wisely to reduce the impact of the environmental parameters. In this context, QCLs are relevant semiconductor lasers because their optical wavelength lies within mid-infrared domains where the atmosphere is highly transparent [2]. The simplest way to generate a chaotic optical carrier from a QCL is to feed back part of its emitted light into the device after a certain time delay [3], beyond which chaos synchronization between the drive and the response QCLs occurs.
A brief overview of the current status of quantum cryptography is given. The results are presented of our preliminary experiments with free-space quantum-key distribution by means of single linearly polarized photons with coded polarization states according to the BB84 protocol, for which purpose a quantum-cryptography communication system is designed. Single photons are detected with a 50% probability using specially designed high-speed photodetectors based on silicon avalanche photodiodes, operated in Geiger mode with active avalanche quenching. A key generation rate of 3.8 kbit/s is obtained, the mean photon number per pulse being 0.2.
This paper reports on the results of experimental investigations into the distribution of a quantum key on a setup designed for quantum cryptography with single photons. The quantum key is transmitted with pulsed semiconductor lasers by coding polarization states of photons in two alternative nonorthogonal bases. Silicon avalanche photodiodes (C30902S) serve as single-photon detectors. The rate of key generation is equal to 1.8 kbit/s when the clock frequency of laser pulse repetition is 100 kHz and the mean number of photons per pulse is approximately equal to 0.2. The number of errors in the key does not exceed 1%.
Experimental research has been conducted in order to establish the new quantum key distribution system for secure and undecipherable quantum communications. The system has been based on optical single-photon transmitters and superconducting single-photon detector receivers. The photon transmitters were based on heavily attenuated femtosecond optical pulses, generated by a high-repetition-rate laser. Novel superconducting devices were designed and developed for efficient and ultrafast counting of visible-light and near-infrared (telecommunication wavelength) photons. The devices were fabricated as nanostructured superconducting NbN serpentine lines with the active area of 100 micrometers squared and operated at 4.2 K inside a cryostat. The detector experimental quantum efficiency reached above 10% for visible-light and up to 8% for near-infrared photons. The dark counts were 0.1 per second. The real-time photon counting rate was above 2 GHz and jitter was 18 ps. In terms of the photon-counting performance, our detectors are significantly better than any competing avalanche photodiodes and photomultipliers.
Communication privacy is one of the key requirements for always expanding networks. Furthermore, fibre systems are becoming saturated and many remote areas do not have access to broadband connection because current systems are too difficult or expensive to deploy. In this work, we experimentally demonstrate a mid-infrared free-space cryptosystem that is based on chaos synchronization between two quantum cascade lasers. Optimal amplitude conditions to ensure both privacy and acceptable deciphering are described, paving the way towards a wide adoption of quantum cascade lasers for future communication systems.