Basic entropy source
Light can be described as quantum particles – called photons.
Our Quantum Random Number Generator (QRNG) is utilizing fluctuations in the vacuum field |0> of light to generate a truly random seed. The vaccum state can be considered as the absense of a photon.
Traditionally, QRNGs based on measurements of the vacuum field use balanced homodyne detection. The vacuum state is mixed in a 50:50 beam splitter with light from a local oscillator and detected by two differentially coupled photo-diodes. However, this kind of optical homodyne detection is challenging to implement in a simple and cost-efficient manner.
Our approach simplifies the detection circuit by allowing for an arbitrary transmissivity η < 1 of the beam splitter and replacing one of the photodiodes by a beam dump. A compact implementatin of this scheme can be made by using the responsitivity of the photo-diode η as the beam splitter. In this way, the entropy source can be realized using a single VCSEL and a photo-diode.
Random number extraction
From the analogue output of the entropy source we extract a high speed sequence of random numbers using an Analogue to Digital Converter (ADC) and an Field Programmable Gate Array.