Figure 5

Detector response to the faked-state attack. For comparison, the black curve shows the normal response to a weak coherent pulse (WCP) attenuated to a single-photon level, containing the zero-photon response (left peak) and the one-photon response (right peak). (a) Fake histogram of output voltage at different faked-state pulse energies (their equivalent mean photon number μ is given in brackets). The detector is blinded with \(0.25~\text{nW} \) CW light. (b) An attack model on a BB84 QKD system with TES as a detector. The threshold (green vertical dashed line) marks the minimum TES voltage output that the system in our model would register as a detection. The fake response is shown for two cases where Bob and Eve pick the same (red) and different (blue) measurement bases under fake pulsed signal of \(2.4\times 10^{-18}~\text{J} \) pulse energy