Quantum Random Number Generation (QRNG) leverages the inherent unpredictability of quantum phenomena to produce truly random numbers. Unlike classical random number generators, which typically rely on complex mathematical algorithms and hence can only produce pseudo-random numbers, QRNG exploits the indeterminacy of quantum processes such as the quantum superposition of states, quantum phase fluctuations, and vacuum noise.

The block diagram depicts the functional elements of a QRNG system. The non-deterministic part is a quantum effect-based randomness or entropy source, such as quantum phase fluctuation. The interferometric unit converts the phase fluctuation into the easily measurable quantity of intensity fluctuation by an unbalanced interferometer. In the detection unit, the photodetector converts the random optical signal into a random electrical signal. The data acquisition and postprocessing unit converts the analog raw random signal into raw random bits and processes them further. The raw data produced by quantum processes may have biases or correlations due to imperfections in the physical setup. This issue is mitigated by post-processing, which mitigates these and ensures the output meets the stringent requirements for a high quality of randomness.