Abstract
Signal state preparation in quantum key distribution schemes can be realized using either an active or a passive source. Passive sources might be valuable in some scenarios; for instance, in those experimental setups operating at high transmission rates, since no externally driven element is required. Typical passive transmitters involve parametric down-conversion. More recently, it has been shown that phase-randomized coherent pulses also allow passive generation of decoy states and Bennett–Brassard 1984 (BB84) polarization signals, though the combination of both setups in a single passive source is cumbersome. In this paper, we present a complete passive transmitter that prepares decoy-state BB84 signals using coherent light. Our method employs sum-frequency generation together with linear optical components and classical photodetectors. In the asymptotic limit of an infinite long experiment, the resulting secret key rate (per pulse) is comparable to the one delivered by an active decoy-state BB84 setup with an infinite number of decoy settings.
Highlights
Quantum key distribution (QKD) is already a mature technology that can provide cryptographic systems with an unprecedented level of security [1,2]
We have introduced a complete passive transmitter for QKD that can prepare decoy-state
In the asymptotic limit of an infinite long experiment, we have proven that such passive scheme can provide a secret key rate lower but comparable to the one delivered by an active decoy-state Bennett–Brassard 1984 (BB84) setup with infinite decoy settings
Summary
Quantum key distribution (QKD) is already a mature technology that can provide cryptographic systems with an unprecedented level of security [1,2]. In a typical quantum optical implementation of this scheme, Alice sends to Bob phase-randomized weak coherent pulses (WCPs) with different mean photon numbers that are selected, independently and randomly, for each signal. These states can be generated using a standard semiconductor laser together with a variable optical attenuator that is controlled by a random number generator (RNG) [19,20,21,22,23]. It has been shown that phase-randomized coherent pulses are suitable for passive preparation of decoy states [37,38] and BB84 polarization signals [42], though the combination of both setups in a single passive source is cumbersome. The paper includes as well some Appendixes with additional calculations
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