Fig. 2

Transmitting module. Two replicas of the depicted fibre-based setup are used by Alice and Bob to transmit light pulses to Charlie. Master and slave lasers’ driving signals are displayed alongside the equipment and are set differently for the two lasers. A power metre connected to the output beam splitter attenuates the outgoing optical pulses to the correct level. The wavelength filter (λ) is for enhancing the indistinguishability of Alice’s and Bob’s photons