Quantum key distribution (QKD) enables secure communication even in the presence of
advanced quantum computers. However, scaling up discrete-variable QKD to high key rates
remains a challenge due to the lossy nature of quantum communication channels and the
use of weak coherent states. Photonic integration and massive parallelization are crucial
steps toward the goal of high-throughput secret-key distribution. We present a fully
integrated photonic chip on silicon nitride featuring a four-channel wavelength-division …

… 47 The sender side of the QKD test setup is implemented as shown in Figure S2. The bit-pattern
48 generator (BPG, Agilent 81141A) is set to a bit rate that corresponds to double of the
QKD 49 symbol rate. Therefore, each time slot corresponds to one bit. Each bit as
generated by the 50 BPG consists of two sample points, such that for lower bit rates a
square signal shape is 51 achieved. … These values 113 are subsequently used to
calculate the splitting lengths needed for the design of the QKD 114 receiver. …