  Single-electron escape from a metastable state over an oscillating barrier is
experimentally investigated in silicon-based ratchet transfer. When the barrier
is oscillating on a time scale characteristic of the single-electron escape,
synchronization occurs between the deterministic barrier modulation and the
stochastic escape events. The average escape time as a function of its
oscillation frequency exhibits a minimum providing a primary signature for
resonant activation of single electrons.
