Time-Dependent Exciton Correlations in Nanoscale Quantum Dot

ABSTRACTIn nanoscale quantum dots, subpicosecond laser pulses can induce and probe strong time-dependent Coulomb correlations between confined electrons and holes. Correlation dynamics for one or two electron-hole pairs driven by both interband and intraband lasers can be simulated by numerical solution of the time-dependent Schrddinger equation within a configuration-interaction description. For example, Coulomb correlations of two electrons and two light holes in a 5×25×25 nm3 GaAs quantum dot yield strong oscillations in the luminescence. Pure correlation effects are revealed by a carefully chosen sequence of three circularly polarized subpicosecond laser pulses. For this case, the Coulomb and electron-laser matrix elements were calculated within the effective-mass approximation with infinite potential walls. For a quantum dot with an internal tunneling barrier that splits the energy levels on the 10 meV scale, correlation effects couple the interband and intraband optical response. Work in progress aims at more realistic geometries, finite outer potential walls, and better description of the band structure, using real-space methods, multi-band models, and tight-binding Hamiltonians. With the help of 'dynamic state selection,' simulation times can be reduced by a factor of 5–10. Dynamic state selection allows the computer, by generic selection criteria, to use only those determinants that are momentarily most important. This approach is especially useful in multi-pulse simulations where the coupled determinants belong to different classes at different times.