Nonmonotonic Field Dependence of Damping and Reappearance of Rabi Oscillations in Quantum Dots

The dynamics of strongly confined laser driven semiconductor quantum dots coupled to phonons is studied theoretically by calculating the time evolution of the reduced density matrix using a numerical path integral method. We explore the cases of long pulses, strong dot-phonon and dot-laser coupling, and high temperatures, which, up to now, have been inaccessible. We find that the phonon-induced damping of Rabi rotations is a nonmonotonic function of the laser field that is increasing at low fields and decreasing at high fields. This results in a reappearance of Rabi rotations at high fields. This phenomenon is of a general nature which occurs for all temperatures and carrier-phonon coupling strengths.

Figure 1

Time dependence of the memory kernel $K(t)$ for a 5 nm spherical GaAs QD at temperature $T=10\mathrm{K}$.

Figure 2

Time evolution of the QD exciton occupation at $T=100\mathrm{K}$ for selected values of the Rabi frequency $f$ exhibiting damped RO. Inset: effective decay time of the RO as a function of $f$ at two temperatures $T$.

Figure 3

QD exciton occupation after excitation with a pulse of fixed duration $\tau$ as a function of pulse area calculated at three different temperatures $T$ and durations $\tau$.

Figure 4

QD exciton occupation as a function of pulse area at $T=10\mathrm{K}$ and $\tau =10\mathrm{ps}$ for coupling constants ${\gamma }_q$ scaled by factors of 1, 5, and 10. Also shown is the result for the unscaled ${\gamma }_q$ at $T=150\mathrm{K}$.