Real time demonstration of high bitrate quantum random number generation with coherent laser light

Abstract

We present a random number generation scheme that uses broadband measurements of the vacuum field contained in the radio-frequency sidebands of a single-mode laser. Even though the measurements may contain technical noise, we show that suitable algorithms can transform the digitized photocurrents into a string of random numbers that can be made arbitrarily correlated to a subset of the quantum fluctuations (High Quantum Correlation regime) or arbitrarily immune to environmental fluctuations (High Environmental Immunity). We demonstrate up to 2 Gbps of real time random number generation that were verified using standard randomness tests.Reliable and unbiased random numbers (RNs) are needed for a range of applications spanning from numerical modeling to cryptographic communications. With the numerous improvements in quantum key distribution (QKD) protocols 1,2 , fast and reliable RN generation is now one of the main technical impediment to highspeed QKD. Whilst there are algorithms that can generate pseudo-RNs, they can never be perfectly random nor indeterministic. True RNs from physical processes may offer a surefire solution.Several physical RN generation schemes have been proposed and demonstrated 3-5 , including schemes based on single photon detections 6-11 . The limit in speed of these systems are in the dead time of photon counters. An alternative quantum approach to photon counting is to use the vacuum fluctuations of an electromagnetic field for RN generation 12,13 . In this letter, we demonstrate a simple scheme to measure and convert vacuum field fluctuations into RNs.The schematic of the quantum RN generator is shown in Fig. 1. A single-mode laser beam at 1550 nm is used as the light source. A few mW of light is split into two equal intensity beams and detected by a pair of photodetectors in a balanced homodyne scheme. When the average laser field amplitude α is significantly larger than the vacuum field fluctuation the subtracted photo-current from the pair of detectors is proportional to αX v (ω), where X v is the quadrature amplitude of the vacuum field. The balanced homodyne setup therefore measures the amplified quadrature amplitude of the vacuum field fluctuations. Only sideband frequencies well above the technical noise frequencies of the laser are used for RN generation (shaded region of the radio frequency (RF) spectrum of Fig. 1(a)). This is achieved by demodulating the photocurrent with an RF frequency (1.6 GHz) followed by a low pass filter. The undulations in the spectra are due to non-uniform RF electronic gain in the photodetectors amplification stages (Fig. 1(b)). Nevertheless, the quantum noise has a constant clearance above the electronic a) Electronic mail: Ping.Lam@anu.edu.au noise level of 8.5 dB. Using a Field-programmable Gate Array (FPGA) a filter function can be programmed to neutralize the non-uniform electronic gain as shown in Fig. 1(c). Finally, using suitable numerical processes, the quantum noise is converted into a sequence of random digital bits as depicted by the 8-bit...

Quantum randomness extraction for various levels of characterization of the devices

“…Consider for instance the probing of an atomic qubit with a laser beam: a laser beam alone can be used to generate randomness [61], but with a different detection scheme than the one used in probing atomic excitations; so it may not be immediate to suggest that one should ignore the atom and extract randomness directly from the laser. For yet other pointer measurements, it may not even be feasible to measure the pointer in a complementary basis (certainly it would be challenging for the Stern-Gerlach setup).…”

Random numbers from vacuum fluctuations

“…the maximum possible amount of entropy one can extract from the source of randomness under the assumption of a Gaussian distribution of the independent random variables X q and X e . An alternative estimation of the entropy in X q assumes that electronic noise is not only known to a third party, but also could be tampered with 17,32 . …”

“…In this paper we report on a quantum random number generator based on measuring vacuum fluctuations as the raw source of ramdomness [16][17][18] . Such measurements have a very high bandwidth compared to schemes based on photon counting 7,9 , and have a much simpler optical setup compared to phase noise measurements [21][22][23][24][25] .…”

“…Since the reflection/transmission of the photon is intrinsically random due to the quantum nature of the process, the unpredictability of the generated numbers is ensured 14 . Other implementations of QRNGs measure the amplified spontaneous emission 15 , the vacuum fluctuations of the electromagnetic field [16][17][18] , or the intensity 19,20 and phase noise of different light sources [21][22][23][24][25] .…”

A New Trend of Pseudo Random Number Generation using QKD

“…As an example, if the frequency tests, the p-value is more than 0.521 and less than 0.687. Which in turn, based on NIST recommendations and others [15,16,18], indicates that the generated raw bits verifies the truly random characteristic.…”