Multiple quantum beats of quantum confined exciton states in InGaAs/GaAs quantum well

TL;DR

This paper reports the first experimental detection of multiple quantum beats in quantum confined exciton states within InGaAs/GaAs quantum wells using spectrally resolved pump-probe techniques, revealing insights into exciton coherence and relaxation.

Contribution

It introduces a novel experimental observation of quantum beats at both positive and negative delays and develops a theoretical model explaining the underlying four-wave mixing contributions.

Findings

Quantum beats observed at positive and negative delays.

Beat frequencies match interlevel exciton spacings.

Decay times are several picoseconds, indicating exciton depopulation as the main relaxation mechanism.

Abstract

Multiple quantum beats of a system of the coherently excited quantum confined exciton states in a high-quality heterostructure with a wide InGaAs/GaAs quantum well are experimentally detected by the spectrally resolved pump-probe method for the first time. The beat signal is observed as at positive as at negative delays between the pump and probe pulses. A theoretical model is developed, which allows one to attribute the QBs at negative delay to the four-wave mixing (FWM) signal detected at the non-standard direction. The beat signal is strongly enhanced by the interference of the FWM wave with the polarization created by the probe pulse. At positive delay, the QBs are due to the mutual interference of the quantum confined exciton states. Several QB frequencies are observed in the experiments, which coincide with the interlevel spacings in the exciton system. The decay time for QBs is of order of several picoseconds at both the positive and negative delays. They are close to the relaxation time of exciton population that allows one to consider the exciton depopulation as the main mechanism of the coherence relaxation in the system under study.