Fast, high quality random numbers from irradiated Josephson junctions

Random number generators are crucial for applications such as Monte Carlo simulations and cryptography, but true randomness is hard to produce. Most practical instances rely on pseudorandom generators or employ costly physical measurements to achieve true randomness, limiting their effectiveness.

Oikawa et al. explored using white noise from a Josephson junction irradiated with high-frequency radio waves as a form of random number generation.

A Josephson junction consists of a pair of superconductors separated by a weak link, such as a barrier or insulator. Due to quantum effects, a current continuously flows without the application of a voltage. Under radio frequency irradiation, a Josephson junction exhibits chaotic oscillation, leading to a white noise output that can be used to generate random numbers.

The authors used a numerical simulation to evaluate a bismuth strontium calcium copper oxide (BSCCO) single crystal intrinsic Josephson junction, determining the quality of its outputs. The quality of a random number set is based on its predictability, reproducibility, and true randomness.

“The quality of the generated random numbers was rigorously evaluated using the [National Institute of Standards and Technology] statistical test suite, which comprises 15 distinct tests for assessing randomness from multiple perspectives,” said author Dai Oikawa. “The random numbers obtained successfully passed all the tests, providing strong evidence of their high quality.”

The team also found that generating random numbers this way was much faster than existing methods, which could make it particularly useful for performing Monte Carlo simulations.

The authors plan to continue their evaluation using experimental testing.

“Building on the results of the numerical analysis, we plan to fabricate a superconducting device and carry out experimental random number generation,” said Oikawa.

Source: “White-noise quality evaluation in chaotic oscillation of Josephson junction for random-number generation,” by D. Oikawa, H. Komatsu, K. Tsuzuki, and H. Andoh, Journal of Applied Physics (2025). The article can be accessed at https://doi.org/10.1063/5.0283866 .