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Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC)

Free space quantum key distribution over 500 meters using electrically driven quantum dot single photon sources

Markus Rau, Tobias Heindel, Sebastian Unsleber, Christian Schneider, Stefan Frick, Gwenaëlle Vest, Sebastian Nauerth, M. Lermer, Martin Kamp, Stephan Reitzenstein, A. Forchel, Sven Höfling, Harald Weinfurter

Published May 1, 2013• 0 citations
Publisher

Abstract

Summary form only given. The field of quantum key distribution has made rapid advances in the past years. Networks of QKD links were implemented, commercial QKD systems are available and research systems have reached GHz repetition rates and distances beyond 200 km. Usually decoy protocols with attenuated laser light pulses are used, where the asymptotic key rate of a QKD system is proportional to the fraction of single photon pulses sent [1]. Single photon sources (SPSs) intrinsically have a higher single photon fraction and thus reach higher key rates.

DOI
10.1109/cleoe-iqec.2013.6801694

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Summary form only given. The field of quantum key distribution has made rapid advances in the past years. Networks of QKD links were implemented, commercial QKD systems are available and research systems have reached GHz repetition rates and distances beyond 200 km. Usually decoy protocols with attenuated laser light pulses are used, where the asymptotic key rate of a QKD system is proportional to the fraction of single photon pulses sent [1]. Single photon sources (SPSs) intrinsically have a higher single photon fraction and thus reach higher key rates.
Highly efficient single-photon sources (SPS) can increase the secure key rate of quantum key distribution (QKD) systems compared to conventional attenuated laser systems. Here we report on a free space QKD test using an electrically driven quantum dot single-photon source (QD SPS) that does not require a separate laser setup for optical pumping and thus allows for a simple and compact SPS QKD system. We describe its implementation in our 500 m free space QKD system in downtown Munich. Emulating a BB84 protocol operating at a repetition rate of 125 MHz, we could achieve sifted key rates of 5–17 kHz with error ratios of 6–9% and -values of 0.39–0.76.
Advances in single-photon sources (SPSs) and single-photon detectors (SPDs) promise unique applications in the field of quantum information technology. In this paper, we report long-distance quantum key distribution (QKD) by using state-of-the-art devices: a quantum-dot SPS (QD SPS) emitting a photon in the telecom band of 1.5 μm and a superconducting nanowire SPD (SNSPD). At the distance of 100 km, we obtained the maximal secure key rate of 27.6 bps without using decoy states, which is at least threefold larger than the rate obtained in the previously reported 50-km-long QKD experiment. We also succeeded in transmitting secure keys at the rate of 0.307 bps over 120 km. This is the longest QKD distance yet reported by using known true SPSs. The ultralow multiphoton emissions of our SPS and ultralow dark count of the SNSPD contributed to this result. The experimental results demonstrate the potential applicability of QD SPSs to practical telecom QKD networks.
Global quantum secure communication can be achieved using quantum key distribution (QKD) with orbiting satellites. Established techniques use attenuated lasers as weak coherent pulse (WCP) sources, with so-called decoy-state protocols, to generate the required single-photon-level pulses. While such approaches are elegant, they come at the expense of attainable final key due to inherent multi-photon emission, thereby constraining secure key generation over the high-loss, noisy channels expected for satellite transmissions. In this work we improve on this limitation by using true single-photon pulses generated from a semiconductor quantum dot (QD) embedded in a nanowire, possessing low multi-photon emission (<10−6<10^{-6}<10−6) and an extraction system efficiency of -15 dB (or 3.1%). Despite the limited efficiency, the key generated by the QD source is greater than that generated by a WCP source under identical repetition rate and link conditions representative of a satellite pass. We predict that with realistic improvements of the QD extraction efficiency to -4.0 dB (or 40%), the quantum-dot QKD protocol outperforms WCP-decoy-state QKD by almost an order of magnitude. Consequently, a QD source could allow generation of a secure key in conditions where a WCP source would simply fail, such as in the case of high channel losses. Our demonstration is the first specific use case that shows a clear benefit for QD-based single-photon sources in secure quantum communication, and has the potential to enhance the viability and efficiency of satellite-based QKD networks.
We have presented a method to estimate parameters of the decoy state protocol based on one decoy state protocol for both BB84 and SARG04. This method can give different lower bound of the fraction of single-photon counts (y1), the fraction of two-photon counts (y2), the upper bound QBER of single-photon pulses (e1), the upper bound QBER of two-photon pulses (e2), and the lower bound of key generation rate for both BB84 and SARG04. The effects of statistical fluctuations on some parameters of our QKD system have been presented. We have also performed the optimization on the choice of intensities and percentages of signal state and decoy states which give out the maximum distance and the optimization of the key generation rate. The numerical simulation has shown that the fiber based QKD and free space QKD systems using the proposed method for BB84 are able to achieve both a higher secret key rate and greater secure distance than that of SARG04. Also, it is shown that bidirectional ground to satellite and inter-satellite communications are possible with our protocol. The experiment of decoy state QKD has been demonstrated using ID-3000 commercial QKD system based on a standard ‘Plug & Play’ set-up. One decoy state QKD has been implemented for both BB84 and SARG04 over different transmission distance of standard telecom fiber.
We report on in-lab free space quantum key distribution (QKD) experiments over 40 cm distance using highly efficient electrically driven quantum dot single-photon sources emitting in the red as well as near-infrared spectral range. In the case of infrared emitting devices, we achieve sifted key rates of 27.2 kbit s −1 (35.4 kbit s −1 ) at a quantum bit error rate (QBER) of 3.9% (3.8%) and a g (2) (0) value of 0.35 (0.49) at moderate (high) excitation. The red emitting diodes generate sifted keys at a rate of 95.0 kbit s −1 at a QBER of 4.1% and a g (2) (0) value of 0.49. This first successful proof of principle QKD experiment based on electrically operated semiconductor single-photon sources can be considered as a major step toward practical and efficient quantum cryptography scenarios.