Quantum key distribution: Weak pulses versus entangled photons

Adarsh Jain, Parthkumar V. Sakhiya, Rajesh Kumar Bahl

Single photon source is indispensable for realization of photon based quantum communication technologies such as quantum key distribution (QKD). Weak coherent pulse source is a practical, efficient and robust solution to generate stream of single photons, probabilistically. In this paper, a methodology for design and development of weak coherent pulse (WCP) source with high count rate of upto 10 Mcps is proposed and implemented. The generation of optical pulses with narrow pulse width and repetition rate of up to 100 MHz is achieved by developing a miniaturized pulse laser module. The weak coherent pulses are generated by heavily attenuating the laser pulses so as to reach the mean photon no. per pulse, μ, close to 0.1. WCP source performance in terms of mean photon number, second order coherence and photon count rate is also investigated. The measured g(2)[0] of ~0.98 shows that the developed WCP source has a very good quality.

Israel J. Owens

Xiongfeng Ma, Chi‐Hang Fred Fung, Hoi‐Kwong Lo

Wenxu Zhao, Tao Wang, Xun Zhou +2 more

Quantum Key Distribution (QKD) provides Alice and Bob with a secure key to prevent third-party eavesdropping. Due to the lack of an ideal single-photon source, weak coherent light sources are widely used. The decoy state method can make up for the security loophole brought by weak coherent light sources - photon number splitting attack (PNS). The specific method of decoy state quantum key distribution is to send light pulses of different intensity levels. Taking the three-intensity decoy state method as an example, one is a signal state with an average photon number of u; one is a decoy state with an average photon number of d; and one is a vacuum state with an average photon number of v. Even if the eavesdropper is more powerful, he cannot distinguish which state the pulse comes from. Therefore, the accuracy of the light pulse intensity is crucial to the security of decoy state quantum key distribution [1] .

Qing-yu Cai, Yong-Gang Tan

In this paper, a photon-number-resolving decoy-state quantum key distribution (QKD) scheme is presented based on recent experimental advancements. A new upper bound on the fraction of counts caused by multiphoton pulses is given, which seems inherent as long as weak coherent sources and high lossy channel are used. This implies that our scheme is optimal in long-distance QKD with weak coherent sources. We show that Eve's coherent multiphoton pulse (CMP) attack is more efficient than a symmetric individual attack when the quantum bit error rate is small, so that the CMP attack should be considered to ensure the security of the final key. Our results show that a not-so-weak pulse can be used to transmit the key. Optimal intensity of the laser source is presented which provides a $23.9\phantom{\rule{0.3em}{0ex}}\mathrm{km}$ increase in the transmission distance.

Christian Kurtsiefer