  Quantum coherent light-matter interactions have been at the forefront of
scientific interest since the fundamental predictions of Einstein and the later
work of Rabi. Direct observation of quantum coherent interactions entails
probing the electronic wavefunction which requires that the electronic state of
the matter does not de-phase during the measurement, a condition that can be
satisfied by lengthening the coherence time or by shortening the observation
time. The short de-phasing time in semiconductors has dictated that all
coherent effects reported to date have been recorded directly only at cryogenic
temperatures. Here we report on the first direct electronic wavefunction
probing in a room-temperature semiconductor. Employing an ultrafast
characterization scheme we have demonstrated Rabi oscillations and self-induced
transparency in an electrically driven, room-temperature semiconductor laser
amplifier, revealing the most intimate details of the light-matter interactions
seen to date. The ability to employ quantum effects in solid-state media, which
operate at elevated temperatures, will finally bring true quantum mechanical
concepts into the realm of practical devices.
