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

Secure quantum key distribution over 40 km of fiber with a pulsed heralded single photon source

Alexandre Soujaeff, Shigeki Takeuchi, Keiji Sasaki, Tsuyoshi Nishioka, Toyohiro Tsurumaru, Toshio Hasegawa, Mitsuru Matsui

Published Jun 1, 2007• 0 citations
Publisher

Abstract

Despite technically successful experiments, most of current quantum key distribution (QKD) systems based on the original BB84 protocols are insecure. The reason is the usage of weak coherent pulses (WCP) as pseudo single photon source (SPS), which allows an eavesdropper to get full information on the key in presence of high optical losses on the transmission channel. To overcome this problem, we have developed a pulse heralded single photon source (HSPS), which we have used for QKD over 40 km of fiber.

DOI
10.1109/cleoe-iqec.2007.4387003

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Despite technically successful experiments, most of current quantum key distribution (QKD) systems based on the original BB84 protocols are insecure. The reason is the usage of weak coherent pulses (WCP) as pseudo single photon source (SPS), which allows an eavesdropper to get full information on the key in presence of high optical losses on the transmission channel. To overcome this problem, we have developed a pulse heralded single photon source (HSPS), which we have used for QKD over 40 km of fiber.
Twin-field quantum key distribution (TF-QKD) can overcome the fundamental rate-loss limit in the point-to-point QKD without a quantum repeater and achieve high key rates over long distances. However, TF-QKD protocol and its variants commonly use weak coherent pulses (WCPs) as light sources. The vacuum part of WCP accounts for a large proportion, resulting in the lower photon detection rate of the communication receiver, which leads to a shorter transmission distance of the secret key. In this paper, we propose an active-decoy TF-QKD protocol with heralded single-photon source (HSPS), which can achieve higher key rate and longer transmission distance than the active-decoy TF-QKD protocol with WCPs. Also, in order to resist the side channel attacks caused by actively modulating intensity of the pulses, we propose a passive-decoy TF-QKD protocol with HSPS to enhance the security, which can perform almost as good as the active-decoy TF-QKD protocol with WCPs.
Mode-pairing quantum key distribution (MP-QKD) is a promising protocol immune to detector side-channel attacks and capable of breaking the repeaterless PLOB bound without global phase locking. Existing MP-QKD protocols employ weak coherent sources (WCSs) with a low probability of single-photon emission, hindering MP-QKD's performance improvement. We propose a new, to the best of our knowledge, MP-QKD protocol using the heralded single-photon source (HSPS) to significantly reduce the vacuum emission probability and increase the single-photon emission rate. Compared with the original WCS-MP-QKD protocol, this protocol has three advantages. First, its maximum transmission distance is extended from 488 km to 560 km. Second, the key rates at 100, 200, 300, and 400 km are 4.4 to 7.4 times those of the original protocol. Third, it does not change the original architecture of MP-QKD and is easy to implement experimentally. This HSPS-MP-QKD protocol has application potential in future metropolitan area QKD networks.
Recently, a long-distance and high-key-rate quantum key distribution (QKD) has become possible by the idea of the decoy state method. We show that a longer distance QKD is possible by utilizing a heralded single-photon source (HSPS) utilizing spontaneous parametric down-conversion as a source instead of a weak coherent pulse (WCP) as proposed in the original decoy state method. Moreover, the key rate is improved by utilizing a presently available photon number resolving detector as a trigger detector of the HSPS, and it is shown to approach the key rate of the WCP.
Secure long distance communication over optical fibres requires robust data encryption. While the encryption itself can be conducted using classical algorithms, there is no unconditionally secure method of classical key distribution. Quantum key distribution (QKD), on the other hand, can provide users of the optical networks with unconditionally secure keys. Since QKD is based on single-photon transmission, one of the challenging tasks is to overcome the distance limitation imposed by the losses in optical fibres. In this work we show that single-photon based QKD outperforms the industry-standard weak coherent pulse approach. We also present our recent experimental results on building a heralded single-photon source based on spontaneous parametric down-conversion of CW light and discuss problems and challenges of heralded single-photon generation in the CW regime.