Evidence of macroscopic coherence at room temperature: Rabi oscillation induced pulse break-up in a quantum dot amplifier

We study experimentally and numerically the changes in pulse shape a Gaussian laser pulse undergoes when propagating through an electrically pumped quantum dot semiconductor optical amplifier (QD-SOA). The pulse energy is set to be resonant to the quantum dot ground state transition, and the pulse shape is analyzed in phase and amplitude in a heterodyne cross-correlation experiment. For the case of an inverted system, we observe the appearance of a periodic modulation of the temporal pulse profile above a critical pulse power. Similar signatures of pulse break-up have been observed at low temperature in quantum dot ensembles without electrical pumping and were linked to optically induced Rabi oscillations imprinting the coherent switching between absorption and stimulated emission of photons by the material system.