Quantum random number generator based on homodyne detection

The need to generate random numbers arises in many scientific and engineering disciplines. There are many types of random number generators with different entropy sources. Historically, two approaches for random number generation have been developed. According to the first method, random numbers can be generated algorithmically, but the resulting sequences in that case are pseudorandom and not suitable for applications in which a high degree of randomness is needed, such as classical or quantum cryptography [1]. These applications require true random numbers obtained by the second method, used indeterminate physical processes. For example, physical random number generators can use quantum processes. All QRNGs provide the necessary physical randomness for generated sequences that can be used in applications requiring high quality random numbers. Existing approaches to quantum random number generation include different implementations: using separation of radiation [2], entangled photon states [3], quantum noise of lasers [4, 5] and photon emission and detection processes [6]. In alternative QRNG systems, quantum vacuum fluctuations are used as the entropy source. In this work, we investigate QRNG is based on quantum vacuum fluctuations [7–9] in which classical detectors are used, however, they can also measure quantum values. The principle of this type of QRNG is based on extracting randomness from quantum noise that appears upon subtracting the balanced detector signals received from beam splitter outputs. To first splitter input (Fig. 1a) a vacuum state is sent, and to other input – a coherent state from laser. On beam splitter these two signals are mixed, then signals from outputs of beam splitter come to balanced detector. One signal from the output of beam the splitter is subtracted from the other and the obtained signal is quantum noise, which can be processed using a PC. A beam splitter is a key element for quantum random number generation schemes based on vacuum fluctuations [7–9]. Mathematical description of a beam splitter, when a strong laser signal, described by the Poisson distribution, arrives at one of its inputs and a vacuum state arrives to other, has been obtained in our previous research [10,11] in the operator form. Also, we obtained mathematical description for fiber Y-splitter (Fig. 1b) and this, with the exception of phase shift, coincided with the previously-obtained expression for the beam splitter [10, 11]. Thus, as description for beam splitter and Y-splitter are equal, we can use Y-splitter for quantum random number generation system, based on homodyne detection.