(Left panel): the on and off states of a metal-insulator-semiconductor field effect transistor (MISFET). The device is “on” when there are charge carriers (electrons) at the semiconductor-insulator interface (channel) to carry current between the source and drain contacts. A negative voltage applied to the gate depletes the channel of charge carriers and turns the device “off.” These two states encode the binary bits 0 and 1. (Right panel): the binary bits 0 and 1 are encoded in the up- and down-spin polarizations of an electron.
