Excitonic and biexcitonic effects in the coherent optical response of semiconductor quantum dots

Pratima Sen, Mohd. Shakil Qureshi, Pratima Sen

Hideki Gotoh, Hidehiko Kamada, T. Saitoh +2 more

Xiaoqin Li, Todd H. Stievater, Yanwen Wu +7 more

Spyridon G. Kosionis, Emmanuel Paspalakis

Hideki Gotoh, Hidehiko Kamada, Tadashi Saitoh +2 more

Exciton-biexciton coherent coupling effects are examined in semiconductor quantum dots. The exciton absorption spectrum is measured with the microphotoluminescence excitation technique in a single InGaAs quantum dot. The spectrum changes from a Lorenztian-type line shape to an unusual dip-shaped line shape with increasing excitation intensities in a higher exciton state where there is a large oscillator strength between the exciton and biexciton states. The intensity dependence of the dip energy width clearly indicates that coherent Rabi oscillation occurs between the exciton and biexciton states. The absorption properties with excitation light of different polarizations show that the dip-shaped spectra only appear when there is a large biexciton state population with linear polarization. A theoretical analysis undertaken with the density matrix method agrees well with experimental results. This agreement reveals that exciton-biexciton coherent interactions lead to unusual absorption spectra and contribute crucially to the optical properties of quantum dots. The exciton-biexciton coherent effects provide a scheme for controlling four distinguishable states, which can be applied to a demonstration of quantum gate operations.

David Gerbasi, Gregory D. Scholes, Paul W. Brumer

Coherent control theory is used to show that one can manipulate biexciton vs exciton populations in semiconductor quantum dots (QDs) in a typical dissipative environment. Both aligned and randomly oriented quantum dots are considered, and population control is shown to be considerable. An application to CdSe QD shows that the proposed coherent control scenario results in a significant reduction in pump intensity for the onset of optical gain.