Multiple-frequency quantum beats of quantum confined exciton states

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. arXiv:1507.04198v1 [cond-mat.mes-hall] 15 Jul 2015

Modeling Quantum Beats by Degenerate Four‐Wave Mixing Spectroscopy in a Single GaAs/AlGaAs Quantum Ring

“…Therefore, their coherent coupling strengths are different, and the contribution to a coherent superposition is not evenly distributed. Therefore, the dominant fine states determine multiple QB periods, and the rest of fine states give negligible QB amplitudes in the Fourier‐transformed frequency spectrum.…”

“…For DFWM signals, we have calculated transient optical nonlinearities of the fine levels in a GaAs/AlGaAs QR by utilizing the semiconductor Bloch equation. When the fine levels of a QR are excited by a pair of picosecond laser pulses, we found that quantum beats (QBs) appear, where time‐integrated DFWM signals oscillate for increasing delay time between the two pulses. The oscillation periods of multiple QBs are dominated by the energy difference of the dominant fine levels, and this method enables to detect a spectral shift of the fine levels for applying an external magnetic field.…”

“…Because the energies of the two eigenstates are different, the phases of the two states evolve at a different rate. Therefore, coherent excitation of two closely spaced excited states gives rise to a nonstationary state, and the phase difference between two states results in a beating modulation of polarization with a period ( T QB = h / δE ), which is called QBs . However, QBs need to be distinguished from polarization interference (PI), which depends on whether the different transitions involved are independent without sharing a common state, but an experimental distinction in oscillating TI‐DFWM signals is not easy.…”

“…This result is consistent with the fact that the excited fine states become correlated in the third order polarization when the Coulomb interaction of electron–hole pairs is considered (Supporting Information). Therefore, this would be the case of multiple QBs …”

Inverse-phase Rabi oscillations in semiconductor microcavities

“…Detailed characteristics of the sample and experimental details can be found in Refs. [29,30]. Figure 5 shows intensities of the pump-probe signals measured at energies corresponding to transitions to the first and fourth quantum-confined levels.…”