Beamsplitter-free, high bit-rate, quantum random number generator based on temporal and spatial correlations of heralded single-photons

TL;DR

This paper presents a high-bit-rate quantum random number generator that leverages spatial and temporal correlations of heralded single photons from SPDC, eliminating the need for a beam splitter and achieving 3 Mbps with high-quality randomness.

Contribution

It introduces a beam splitter-free, high-rate QRNG using spatial and temporal correlations of photon pairs from a non-collinear SPDC source, enhancing bit rate and randomness quality.

Findings

Achieved 90 million raw bits in 27.7 seconds.

Generated a 3 Mbps random bit stream passing standard tests.

Demonstrated potential for further rate enhancement through more ring sectioning.

Abstract

The spontaneous parametric down-conversion (SPDC), an inherently random quantum process, produces a non-deterministic photon-pair with strong temporal and spatial correlations owing to both energy and momentum conservation. Therefore, the SPDC-based photon pairs are used for quantum random number generation (QRNG). Typically, temporal correlation in association with an ideal unbiased beam splitter is used for QRNG without fully exploring the spatial correction. As a result, SPDC-based QRNG has a low bit rate. On the other hand, due to the spatial correlation, the photon pairs in non-collinear phase-matched geometry are generated randomly in diametrically opposite points over an annular ring spatial distribution. Therefore, exploring the temporal correlation between photon pairs from different sections of the annual ring can lead to multi-bit QRNG at a high rate, avoiding the need for a beam splitter. As a proof-of-concept, we report on high-bit-rate QRNG by using spatial correlation of photon-pairs by sectioning the SPDC ring of a non-collinear, degenerate, high-brightness source and temporal correlation between the diametrically opposite sections. Dividing the annular ring of the high-brightness photon-pair source based on a 20 mm long, type-0 phase-matched, periodically-poled KTP crystal into four sections, recording the timestamp of the coincidences (widow of 1 ns) between photons from diametrically opposite sections and assigning bits (0 and 1), we extracted 90 million raw bits over 27.7 s at a pump power of 17 mW. We determined the extraction ratio using the minimum entropy evaluation of more than 95% in our case. Using Toeplitz matrix-based post-processing, we achieved a QRNG with a bit-rate of 3 Mbps, passing all NIST 800-22 and TestU01 test suites. The generic scheme shows the possibility of further enhancement of the bit rate through more sectioning of the SPDC ring.