Controlling Coherent Light-Matter Interactions in Semiconductors

Kevin F. MacDonald, Eric Plum, Daniele Faccio +1 more

Mirco Kolarczik, Nina Owschimikow, Julian Korn +6 more

Coherence in light–matter interaction is a necessary ingredient if light is used to control the quantum state of a material system. Coherent effects are firmly associated with isolated systems kept at low temperature. The exceedingly fast dephasing in condensed matter environments, in particular at elevated temperatures, may well erase all coherent information in the material at timescales shorter than a laser excitation pulse. Here we show for an ensemble of semiconductor quantum dots that even in the presence of ultrafast dephasing, for suitably designed condensed matter systems quantum-coherent effects are robust enough to be observable at room temperature. Our conclusions are based on an analysis of the reshaping an ultrafast laser pulse undergoes on propagation through a semiconductor quantum dot amplifier. We show that this pulse modification contains the signature of coherent light–matter interaction and can be controlled by adjusting the population of the quantum dots via electrical injection. Quantum coherence effects are often only visible at low temperatures, where dephasing times are not too short. Here Kolarczik et al. show that quantum coherence effects can appear in the reshaping of ultrafast laser pulses passing through quantum dots even at room temperature.

Jean-Louis Le Gouët

Le Gouët

G. Eisenstein, Johann Peter Reithmaier, Amir Capua +4 more

Light matter coherent interactions require that the coherent state induced in the matter be maintained for the duration of the observation. The only way to induce and observe such interactions in room temperature semiconductors, where the coherence time is of the order of a few hundred femtoseconds, is to use ultrashort pulse excitations and an ultrafast characterization technique. For media comprising an ensemble of nanostructure semiconductors such as self-assembled quantum dots, the gain broadening inhomogeneity also affects the interaction. Moreover, when gain media in the form of an active waveguide, such as optical amplifiers, are used, the interaction is distributed and includes nonresonant incoherent phenomena that occur simultaneously with the coherent effects. Such a complex system can exhibit, nevertheless, clear coherent interactions even at room temperature. Using InAs/InP quantum dot and wirelike quantum dash amplifiers, Rabi oscillations, self-induced transparency, coherent control using spectral pulse shaping, Ramsey interference, and photon echo have been demonstrated. The characterization employed cross frequency resolved optical gating, and the experiments were accompanied by a comprehensive finite difference time domain model that solves the Maxwell and Lindblad equations. This work has major implications on the understanding of the details of dynamical processes in active semiconductor devices, on short pulse generation from semiconductor lasers, and on various future quantum devices.

Ataç İmamoğlu