Abstract
A protocol with the potential of beating the existing distance records for conventional quantum key distribution (QKD) systems is proposed. It borrows ideas from quantum repeaters by using memories in the middle of the link, and that of measurement-device-independent QKD, which only requires optical source equipment at the userʼs end. For certain memories with short access times, our scheme allows a higher repetition rate than that of quantum repeaters with single-mode memories, thereby requiring lower coherence times. By accounting for various sources of nonideality, such as memory decoherence, dark counts, misalignment errors, and background noise, as well as timing issues with memories, we develop a mathematical framework within which we can compare QKD systems with and without memories. In particular, we show that with the state-of-the-art technology for quantum memories, it is potentially possible to devise memory-assisted QKD systems that, at certain distances of practical interest, outperform current QKD implementations.
Highlights
Despite all commercial [1] and experimental achievements in quantum key distribution (QKD) [2,3,4,5,6,7,8,9,10], reaching arbitrarily long distances is still a remote objective
The number of rounds that it takes to load both memories is max {NA, NB}. Once both memories are loaded, the rest of the protocol is similar to that of original measurement-device-independent QKD (MDI-QKD) in terms of rate analysis: the quantum memory (QM) replace the sources in figure 1(c) and the total transmission-detection efficiency is replaced by the reading-measurement efficiency in the Bell-state measurement (BSM) module
What we have proposed here is an initial step toward improving the performance of QKD systems by using QMs
Summary
Despite all commercial [1] and experimental achievements in quantum key distribution (QKD) [2,3,4,5,6,7,8,9,10], reaching arbitrarily long distances is still a remote objective. Our memory-assisted MDIQKD is similar to a single-node quantum repeater, except that there is no memories at the users end This way, similar to quantum repeaters, we achieve a rate-versus-distance improvement as compared to the MDI-QKD schemes proposed in [18, 28,29,30], or other conventional QKD systems that do not use QMs. There is an important distinction between our protocol and a conventional quantum repeater system that relies on single-mode memories. The repeat period is constrained by the writing time, including the time needed for the herald/verification process, into memories This implies that using sufficiently fast memories, i.e., with short writing times, one can run our scheme at a faster rate than that of a quantum repeater, thereby achieving higher key generation rates, as compared to conventional QKD links, and at lower coherence times, as compared to probabilistic repeater systems.
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