We present a security analysis against collective attacks for a time–energy entanglement-based quantum key distribution protocol, given the practical constraints of single-photon detector efficiency, channel loss, and finite-key considerations. We find a positive secure-key capacity when the key length increases beyond 10[superscript 4] for eight-dimensional systems. The minimum key length required is reduced by the ability to post-select on coincident single-photon detection events. Including finite-key effects, we show the ability to establish a shared secret key over a 200 km fiber link.
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