Fig. 1: BB84-QKD setup employing an atomically thin single-photon source.

a The transmitter (Alice) comprises a strain-engineered WSe₂ monolayer inside a closed-cycle cryocooler, a diode laser with variable repetition rate, dielectric filters, and an optical fiber together with a polarizer for adjusting the polarization states. Alice sends single-photon pulses with fixed polarization (H, V, D, A) to the receiver (Bob). Inside the quantum channel, losses can be introduced using a variable attenuator. Bob comprises a four-state polarization analyzer based on bulk polarization optics. b Emission spectra of the WSe₂ monolayer sample recorded at different locations in the setup: before (blue) and after (orange) spectral filtering and coupling to the SM fiber. The selected quantum emitter emits at a wavelength of 807 nm. c Second-order autocorrelation histograms of the triggered quantum emitter at clock rates of 2.5, 5.0, and 10.0 MHz. The autocorrelation is evaluated from the events registered at all four receiver channels.