Observation of Bloch oscillations in a semiconductor superlattice

We investigate the polarization decay in biased superlattices with transient degenerate four-wave mixing. The signals have a strong periodic modulation in the field regime where the cw optical spectra show the transitions of a Wannier-Stark ladder. The period of the oscillations is in excellent agreement with Bloch oscillation theory. The oscillation period can be tuned over a large range by varying the electric bias field in the superlattice.