Room-temperature initialization, dynamics, and measurement of coherent electron spins in strongly confined quantum dots

摘要

Semiconductor quantum dots provide a platform for studying and exploiting individual electron spins as they interact with a complex solid state environment. Colloidal nanocrystal quantum dots are of particular interest for potential applications, because they can achieve sufficient confinement to operate at room temperature with relatively robust electron spin coherence. The strong confinement in these nanostructures leads to significant effects caused by mixing of valence subbands and variation in particle size and shape. These effects influence the processes of carrier spin initialization and detection. We have performed ensemble time-resolved Faraday rotation experiments as well as single-dot photoluminescence excitation measurements to study how the strong quantum confinement affects the spin physics in these systems. Single dot PLE measurements reveal mechanisms of transition broadening that are relevant at room temperature, including thermal broadening and spectral diffusion due to mobile charges in the surrounding environment. We find that the mixing of valence subbands in the confined hole states largely determines the efficiency of optical spin pumping and Faraday-rotation-based spin detection. By studying these effects, we take a step towards controlling and exploiting spin coherence in this flexible room temperature platform.