Fig. 1: Schematic diagram of QRNG devices based on various quantum principles.

BS: beam splitter 50/50, PD: photodetecotr, SPD: single-photon detector, ADC: analogue to digital converter, PID: proportional-integral-derivative control, PS: phase-shifter, DL: delay line, Amp: amplifier. a Single-photon-detection QRNG. b Phase-fluctuation QRNG. c Photon-counting-detection QRNG. d Vacuum-fluctuation QRNG.