Random-Number Generation Using Chaos in RF-Irradiated Stacked Intrinsic Josephson Junction

The configuration of a robust, high-security system has become increasingly important because, as computer processing speeds continue to improve, the vulnerabilities of cryptographic systems that rely on conventional pseudo-random-numbers have raised concerns regarding potential leaks of confidential information. To establish such a secure system, high-quality and high-speed random numbers are essential. Here, high-quality random-numbers are defined as statistically unbiased, non-reproducible, and unpredictable values. One approach to generating such numbers is to exploit physical random phenomena, such as chaos. In particular, chaos in Josephson junctions (JJs) under radio-frequency (RF) irradiation has been identified as a suitable mechanism for random-number generation. In this study, we considered RF-biased intrinsic Josephson junctions (IJJs) in a mesa-type Bi <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$_{2}$</tex-math></inline-formula> Sr<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$_{2}$</tex-math></inline-formula>CaCu <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$_{2}$</tex-math></inline-formula> O<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$_{8+\delta }$</tex-math></inline-formula> single crystal. Since the interactions among stacked IJJs must be considered, it is insufficient to evaluate their properties using the conventional resistively and capacitively shunted junction (RCSJ) circuit model. Instead, we numerically investigated the chaotic voltage of an IJJ stack irradiated with higher frequencies than those typically used in conventional RF systems, employing the capacitively coupled JJ model with diffusion current, which incorporates interlayer interactions. Based on the time-series output voltage of the IJJ, we then generated random-numbers and evaluated their quality using statistical tests.