Electron cooling and control of Josephson current at sub-Kelvin temperatures

The factors limiting cooling electrons by biased tunnel junctions have been considered. At low temperature range the deviation from equilibrium, superconductor overheating and states within the superconductor gap limit the achievable minimum temperature. Strong increase of electron-phonon coupling at higher temperature limits the temperature range of effective electron cooling to sub-Kelvin region. Control of Josephson coupling in superconductor-normal metal-superconductor weak link by electron cooling in normal electrode has been demonstrated experimentally.