Electronic devices and circuits containing components, manufactured from ‘superconductive’ materials, specially designed for operation at temperatures below the ‘critical temperature’ of at least one of the ‘superconductive’ constituents and having any of the following: (a) Current switching for digital circuits using ‘superconductive’ gates with a product of delay time per gate (in seconds) and power dissipation per gate (in watts) of less than 10 – 14 J; or (b) Frequency selection at all frequencies using resonant circuits with Q-values exceeding 10 000 ;