Speaker
Description
We theoretically study light scattering (resonance fluorescence, RF) on a single self-assembled quantum dot (QD) in the weak excitation limit. We show that coupling to the phonon continuum at moderate coupling strengths (which holds, e.g., for InAs/GaAs QDs) leads to a Fano-like line profile near the resonant energy, which is due to the interplay of a narrow inelastic scattering line stemming from noise-induced transient dynamics and a broad phonon sideband. In the weak-coupling limit, the spectral profile attains an exact Fano shape, with a complete suppression of resonant light scattering. Due to the super-Ohmic character of the phonon reservoir, with vanishing spectral density at the QD transition energy, the narrow Fano feature in the scattering spectrum appears only at finite temperatures and grows linearly with temperature, but has a temperature-independent width that depends only on the exciton dephasing time.
Phonon effects in linear and nonlinear QD spectroscopy are now well understood. It has been established that the absorption, emission, or four-wave mixing spectrum is composed of a narrow central line, which is not broadened by phonons due to the super-Ohmic nature of this reservoir, and a broad, strongly temperature-dependent phonon sideband. A similar structure was predicted for RF under pulsed excitation [1]. On the other hand, our studies of the effect of classical white noise on the RF under cw excitation [2,3] show that noise-induced transient dynamics give rise to non-elastic scattering, manifested by a broadened spectral feature at the transition frequency, in contrast to the laser-linewidth-limited Rayleigh scattering line located at the laser frequency.
Here we use a two-level independent boson model of a QD coupled to LA phonons via deformation potential. We solve the Lindblad equation for the system evolution in the presence of spontaneous emission in the leading order in optical excitation, while treating phonons exactly. The RF spectrum under cw excitation is computed using the Lax theorem for the two-point autocorrelation function. As a result, we show that the spectrum at slightly detuned excitation is composed of a narrow inelastic feature, with a temperature-independent width and strength proportional to temperature, and a broad phonon sideband. As the detuning is decreased, the broad phonon background raises as a result of growing overall scattering intensity, while the narrow feature evolves from a mostly absorptive shape via dispersive to a spectral dip around the transition frequency, resulting in a considerable suppression of scattering for coupling strengths typical, e.g., for GaAs. The effect can be shown to result from the presence of reservoir memory (colored noise) rather than its quantum nature.
[1] K. J. Ahn, J. Förstner, and A. Knorr, Phys. Rev. B 71, 153309 (2005).
[2] R. A. Bogaczewicz, and P. Machnikowski, New J. Phys. 25, 093057 (2023).
[3] R. A. Bogaczewicz, and P. Machnikowski, Opt. Lett. 50, 888 (2025).
