The nanostructure consisting of two superconductors through a semiconductor or an insulator is called a Josephson junction. Josephson junctions are fundamental electronic devices for quantum computers and are also highly important for practical applications. When multiple Josephson junctions coherently couple through a shared superconductor, electronic states called Andreev molecules are formed. In this configuration, it becomes possible to control the supercurrent flowing through one junction by the other junction (nonlocal Josephson effect) due to the Andreev molecules. This represents significant physics that leads to new control methods for Josephson junctions and novel applications. Our research aims to pioneer the fundamental understanding of Andreev molecules, discover new physical phenomena arising from coherent coupling of multiple Josephson junctions, and explore technologies leading to next-generation quantum computing, including Majorana Fermions.
Many aspects of nonequilibrium statistical thermodynamics needs to be clarified. In nanoscale electronic devices, precisely controlled non-equilibrium environments can be realized and observed through the application of bias voltages, irradiation with high-frequency microwave, and phonon excitation. Furthermore, advancements in charge measurement techniques allow for the real-time tracking of individual electron motion. We focus on the quantum tunneling phenomena of single electrons occurring within low-dimensional semiconductor nano-devices such as quantum dots. By measuring the quantum tunneling phenomena of charge and spin in both equilibrium and non-equilibrium environments in real-time, we aim to elucidate the fundamental laws governing the statistical properties of electrons within quantum dots.