  We report on the electron analog of the single photon gun. On demand single
electron injection in a quantum conductor was obtained using a quantum dot
connected to the conductor via a tunnel barrier. Electron emission is triggered
by application of a potential step which compensates the dot charging energy.
Depending on the barrier transparency the quantum emission time ranges from 0.1
to 10 nanoseconds. The single electron source should prove useful for the
implementation of quantum bits in ballistic conductors. Additionally periodic
sequences of single electron emission and absorption generate a quantized
AC-current.
