Abstract
The decoy-state method in quantum key distribution (QKD) is a popular technique to approximately achieve the performance of ideal single-photon sources by means of simpler and practical laser sources. In high-speed decoy-state QKD systems, however, intensity correlations between succeeding pulses leak information about the users' intensity settings, thus invalidating a key assumption of this approach. Here, we solve this pressing problem by developing a general technique to incorporate arbitrary intensity correlations to the security analysis of decoy-state QKD. This technique only requires to experimentally quantify two main parameters: the correlation range and the maximum relative deviation between the selected and the actually emitted intensities. As a side contribution, we provide a non-standard derivation of the asymptotic secret key rate formula from the non-asymptotic one, in so revealing a necessary condition for the significance of the former.
Highlights
Quantum key distribution [1, 2, 3] (QKD) is a technique that enables secure and remote delivery of cryptographic keys based on the laws of quantum mechanics
In real-life implementations, the information carrier of quantum key distribution (QKD) is the quantum of light or photon, and due to the low transmissivity of single photons in typical optical channels —which, for instance, in the case of optical fibers decreases exponentially with the fiber length [6, 7, 8, 9]— one major challenge consists of achieving high secret key generation rates at long distances
We consider a standard polarization encoding decoy-state BB84 protocol [15], our results can be readily extended to any QKD protocol that relies on decoy-states
Summary
Quantum key distribution [1, 2, 3] (QKD) is a technique that enables secure and remote delivery of cryptographic keys based on the laws of quantum mechanics. In real-life implementations, the information carrier of QKD is the quantum of light or photon, and due to the low transmissivity of single photons in typical optical channels —which, for instance, in the case of optical fibers decreases exponentially with the fiber length [6, 7, 8, 9]— one major challenge consists of achieving high secret key generation rates at long distances. For this purpose, one natural approach is to increase the repetition rate of the laser source in the transmitter station. For repetition rates of the order of GHz, it has been shown that intensity correlations between succeeding pulses appear [10, 11], potentially opening a security loophole
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