Figure 1.

Scheme of the experiment. A continuous wave (CW) laser beam at 1550 nm is curved into pulses by an intensity modulator (IM) with a 5 kHz repetition rate and a 10 ns pulse width. The variable optical attenuator (VOA) decreases the mean number of photons per pulse (μ) to be lower than one. On-chip Mach-Zehnder interferometers (MZIs), controlled by an FPGA, create the quantum states. A combination of VOA₁ and MZI₀₀ enable a decoy state technique with multiple and different numbers of photons per pulse. The quantum states are then measured independently by Bob’s chip, creating an interference between pairs of cores. In this way parallel keys are generated between Alice and Bob. The rectangle insets show Alice’s (9.5 × 2.5 mm) and Bob’s (10 × 2.5 mm) silicon chips.