A current-controlled switching device based on superconductivity for use primarily in computer circuits. The early version has been superseded by the tunneling cryotron, which consists basically of a Josephson junction. In its simplest form (see illus.) the device has two electrodes of a superconducting material (for example, lead) which are separated by an insulating film only about 10 atomic layers thick. For the electrodes to become superconducting, the device has to be cooled to a few degrees above absolute zero. The tunneling cryotron has two states, characterized by the presence or absence of an electrical resistance. They can be considered as the “on” and “off” states of the switch, respectively. Switching from on to off is accomplished by a magnetic field generated by sending a current through the control line on top of the junction. The device can switch in a few picoseconds and has a power consumption of only some microwatts. These properties make it an attractive switching device for computers, promising performance levels probably unattainable with other devices.