Excitonic Rabi oscillations in self-assembled quantum dots in the presence of a local field effect

We experimentally studied the excitonic Rabi oscillations in self-assembled semiconductor quantum dots using two-pulse photon echo spectroscopy. We observed the change in the shape of the Rabi oscillations by the second pulse intensity. Our experimental results were systematically reproduced by numerical calculations taking into account the local field effect arising from the Coulomb interaction between photoinduced charge densities in a quantum dot. Our experimental findings indicated that the local field effect contributes considerably to the coherent optical responses of the excitons in quantum dots.

Figure 1

(a) AFM image (scan size 1 $\mu$m${}^2$) of the uncapped sample. (b) PL spectrum at 3.5 K. The excitation photon energy was 2.9 eV. (c) PE intensity detected as a function of $\tau$. The red line shows a single exponential fitting curve with ${\tau }_{\text{dec}}=630$ ps.

Figure 2

(a) PE intensity plotted as a function of $\sqrt{I_1}$ and numerically calculated PE intensity vs ${\theta }_1$ for simple two-level systems at $\tau =100$ ps. (b) Dependence of the dephasing time on $\sqrt{I_1}$.

Figure 3

(a) The PE intensity detected as a function of $\sqrt{I_1}$ for various values of $I_2$. (b) Numerical calculations of the PE intensity with LFE ($\hslash \Delta \omega =22$ $\mu$eV) as a function of ${\theta }_1$ for various values of ${\theta }_2$.

Figure 4

Rotation of the Bloch vector when (${\theta }_1,{\theta }_2$) are $(0.05\pi ,0.4\pi )$, $(0.4\pi ,0.4\pi )$, and $(0.8\pi ,0.4\pi )$. The double-headed arrow represents $\Delta {\rho }_D$.