Carrier relaxation and quantum decoherence of excited states in self-assembled quantum dots

We report systematic measurements of photoluminescence excitation spectra and dephasing times ${(T}_2’\mathrm{s})$ on various excited states of hundreds of individual quantum dots (QDs). From the variation of $T_2’\mathrm{s}$ with the energy separation between excited states and the ground state ${(E}_{\mathrm{rel}}),$ we identified two distinct regions of $E_{\mathrm{rel}}$ where LO phonon emission and hole relaxation via LA phonon emission play as dominat dephasing mechanisms. We also found a clear evidence of significantly slow energy relaxation in the $E_{\mathrm{rel}}$ range where these phonon emission processes are suppressed due to the reduction of interaction phase space.