Single quantum dot states: Energy relaxation and coupling

Summary form only given. In the late 1990s, numerous groups have reported studies of the optical spectrum of individual quantum dots (QDs) successfully removing the spectral blurring caused by inhomogeneous broadening in ensemble measurements. These developments have now enabled the study of the coherent optical response and the demonstration of transient coherent control in a single QD. Most single QD experiments have used photoluminescence (PL) techniques to probe the system. Extending the methodology used to report on the resonant nonlinear optical response, we now report the measurement of the energy relaxation rate between QD states and obtain information about the nature of the state coupling. The measurements show evidence for incoherent coupling between states with fast energy relaxation. In contrast, the coupling between states belonging to the same fine structure doublet is very strong showing signatures that these states may be coherently coupled.