Resonance fluorescence and superfluorescence of intersubband transitions

Abstract

Intersubband transitions are unbound electronic transitions of doped quantum wells, semiconductors heterostructures with a planar symmetry. I theoretically studied the fluorescence of a strongly pumped intersubband transition, finding that the many electron nature of such a system leads to a modification of the usual Mollow triplet. In particular, the intensity of the central peak in the fluorescence spectrum becomes a function of the electron coherence, allowing access to the coherence time of a quasi two-dimensional electron gas through a fluorescence intensity measurement. Moreover, while transitions between the two states of the ac Stark-split doublet are forbidden in centrosymmetric systems, and thus almost impossible to observe in experiments performed with atoms they become allowed in asymmetric quantum wells, in which the wave function symmetry can be broken. I developed a many-body theory describing also this intradoublet emission, showing that by using doped asymmetry, the emission can be orders of magnitude higher than in previously studied systems. This opens the way to the realization of monolithic and tunable terahertz emitters since the Rabi frequency at which this emission occurs lies in the terahertz range and can be tuned by the pump power. Finally, I have investigated if superfluorescence can occur in intersubband transitions. In order to do so I used a general quantum master equation that includes dephasing and nonradiative emission to model the many-body system in solid state. Performing a second-order approximation allowed to obtain a closed system of equations that were studied analytically and numerically, verifying that in the regimes characteristic of intersubband transitions cooperative effects leading to powerful bursts of light could be observed experimentally.

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ORCID for Simone De Liberato: orcid.org/0000-0002-4851-2633

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