Development of a QRNG front-end for shot noise measurement : analysis of quantum shot noise originating from photodiodes

Abstract: As one of the more mature quantum technologies, quantum random number generators (QRNGs) fill an important role in producing secure and private keys for use in cryptogra- phy in e.g. quantum key distribution (QKD) systems. Many available QRNGs are expen- sive and optical QRNGs often require complex optical setups. If a reliable QRNG could be implemented using less expensive components they could become more widespread and be used in common applications like encryption and simulation. Shot noise is a possible entropy source for these kinds of random number generators. For such a generator to be classified as a QRNG the origin of the shot noise must be controlled and verifiable. This project aims to investigate how an entropy source could be implemented using the shot noise generated by an illuminated photodiode. This requires the design and construction of the accompanying electro-optical front-end used to prepare a signal for sampling. The successful estimation of the electron charge e is used as a way to verify that shot noise is present in the sampled signal. Suitable component values and operating points are also in- vestigated and it is shown that quite low gain (10 000) is suitable for the current-to-voltage amplifier which amplifies the signal generated by the photodiode. For this configuration an estimate of e was achieved with a relative error of 3%. In conclusion this is a promising and interesting approach for generating random numbers at high rates and at low cost. Whether the correct estimation of e is enough to certify that the device is sampling noise from the quantum regime is however not completely clear and further investigation is likely needed.