On the passive probing of fiber optic quantum communication channels
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On the Passive Probing of Fiber Optic Quantum Communication Channels A. V. Korol’kova, K. G. Katamadzeb, S. P. Kulikb, and S. N. Molotkova,c,d a
Academy of Cryptography of the Russian Federation, Moscow, 121552 Russia email: [email protected] b Faculty of Physics, Moscow State University, Moscow, 119899 Russia c Institute of Solid State Physics, Russian Academy of Sciences, Chernogolovka, Moscow oblast, 142432 Russia d Faculty of Computational Mathematics and Cybernetics, Moscow State University, Moscow, 119899 Russia Received September 4, 2009
Abstract—Avalanche photodetectors based on InGaAs:P are the most sensitive and only detectors operating in the telecommunication wavelength range 1.30–1.55 µm in the fiber optic quantum cryptography systems that can operate in the single photon count mode. In contrast to the widely used silicon photodetectors for wavelengths up to 1 µm operating in a waiting mode, these detectors always operate in a gated mode. The pro duction of an electron–hole pair in the process of the absorption of a photon and the subsequent appearance of an avalanche of carriers can be accompanied by the inverse processes of the recombination and emission of photons. Such a backward emission can present a potential serious problem for the stability of fiber optic quantum cryptography systems against passive probing. The results of analyzing the detection of backscat tered radiation are reported. The probability of such an emission has been estimated. DOI: 10.1134/S1063776110040023
1. INTRODUCTION
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Within the last decade, the transmission of confi 1
dence information using quantum states has been developed from theoretical ideas to real engineering solutions and sometimes to technologies [1–3]. The security of keys in quantum cryptography is based on fundamental quantummechanical exclusions rather than on engineering or computational restrictions. Quantum cryptography implies that only transmitter and receiver communication sides are controlled, 2
distinguishability of nonorthogonal quantum states. Any attack on the communication channel in order to obtain information of a transmitted quantum state results in its perturbation and appearance of errors on the receiver side. In real imperfect systems, errors on the receiver side appear even in the absence of the eavesdropper. For each quantum key distribution pro tocol, there is a critical error up to which the key can be distributed with guaranteed security. Since errors induced by own noise and errors induced by the eaves dropper are fundamentally indistinguishable, all the errors should be attributed to the action of the eaves dropper. In fiber optic quantum cryptography systems, a source of quantum states is not strictly singlepho
whereas a quantum communication channel through which quantum states are transmitted is not controlled and is available for any active manipulations and mod ifications by an eavesdropper up to a change of the channel to another, more perfect communication channel. In addition, it is assu
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