Fig. 3: Secret key rate performance of DI-QKD.

a Asymptotic DI Devetak-Winter secret key rate as a function of the distance^115,116,117. An idealized scenario is assumed where Alice and Bob implement unit efficiency measurements on their shares of a perfect Bell pair, delivered by an entanglement source equidistant from both of them. Moreover, the standard approach where undetected signals are mapped to a fixed outcome is presumed for the closure of the detection loophole. Noticeably, even in this idealized setup, the absence of a heralding mechanism implies that the distance covered by DI-QKD is below 3.5 km, considering an attenuation coefficient of 0.2 dB/km (referred to the third telecom window). The limited-efficiency model is considered for the channel loss³⁶. b, c Finite secret key rate as a function of the QBER and the number of transmitted signals, n, assuming a depolarizing-noise model for a perfect Bell pair and no losses of any kind. For illustration purposes, some typical finite-key parameters are selected. Both figures, b and c, are reproduced from ref. ⁴⁰ under the Creative Commons license.