Fig. 2: Performance evaluation of the WSe₂ single-photon source device for applications in QKD.

a Excitation power resolved series of the click rate and g⁽²⁾(0). The source reaches saturation at 52.5 μW. Solid lines are a guide to the eye. Error bars are the standard deviations. b Input–Output characterization of Bob for extraction of the QBER. The detection rates in kHz observed at each channel are stated and additionally encoded in the field’s opacity. c Rate-loss diagram considering the experimental data from a. Although the g⁽²⁾(0) is not at the minimum at saturation, the achievable distance and secret key rate for each distance has its maximum at saturation. d Real-time security monitoring over exemplary time of 1.5 h (P = 0.43P_sat, H-input polarization). The QBER is calculated from all registered events. In full implementations using only subsets for an estimation, this value might be higher. Antibunching g⁽²⁾(0) of the single-photon source evaluated by correlating all registered events in non-overlapping blocks for 10 s (blue) and 100 s (orange) accumulation time (exemplary g⁽²⁾(τ) histograms shown as insets). See Supplementary Fig. 6 for details on the accumulation time.