Light on a beam splitter: More randomness with single photons

Abstract

AbstractOne of the most fundamental quantum random number generators is implemented with light impinging onto a beam splitter, and two single photon detectors at its output. Often, this generator is described as “a photon which takes one or other path towards a detector”. The input state of light in conjunction with the detector response is relevant for the amount, the pattern, and the correlation of the generated clicks. Only a fraction of all generator outcomes, the min‐entropy, can be used as a further resource for true randomness. This paper addresses the difference in the common description with incoming single photons and the often implemented scheme with a weak coherent light source, such as an attenuated laser. For this very fundamental and widely used configuration the amount of usable entropy is compared. If single photons from an anti‐bunched light source are supplied, the amount of entropy is higher than for the case of a supplied coherent state – although the latter can be arbitrarily bright unlike the single photon source. image