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

Spontaneous parametric down-conversion (SPDC), an inherently random quantum process, produces pair photons with strong temporal and spatial correlations due to energy and momentum conservation, and acts as the key for quantum random number generation (QRNG). Standard QRNG methods primarily use temporal correlations with beam splitters, limiting bit rates. However, due to spatial correlation, the pair photons in non-collinear phase-matched SPDC-setup appear at diametrically opposite points on an annular spatial distribution. Therefore, exploring the temporal correlation between the spatially correlated photon-pairs from different sections of the annual ring can directly lead to device-independent, multi-bit QRNG at a high rate, eliminating the need of a physical object such as 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 (window of 1 ns) between photons from diametrically opposite sections and assigning bits (0 and 1), we extracted 90 × 10⁶ raw bits over 27.7 s at a pump power of 17 mW. Using minimum entropy evaluation, we determined an extraction ratio of over 95 % for raw bits. Further, using Toeplitz matrix-based post-processing, we developed QRNG with bit rate of 3 Mbps, passing all NIST 800-22 and TestU01 test suites. The generic scheme shows the possibility of further enhancement of bit rate with more sectioning of the SPDC ring.