ELECTRON CORRELATION EFFECTS ON RELAXATION AND DECOHERENCE TIMES IN A QUANTUM DOT

Abstract

We use density matrix theory to calculate decay rates of lowest-lying eigenstates in rotationally symmetric quantum dots (QDs). Specifically, we investigate relaxation and decoherence times in single-electron and three-electron systems, where in the latter Coulomb interaction is included. Both systems are studied with and without Rashba and Dresselhaus spin-orbit (SO) effects. Two SO strengths are investigated: A small strength which is more typical of GaAs QDs and a larger strength to better reveal the influence of SO on decay rates. In the single-electron case we consider three different types of electron-phonon interactions as a source of decay: The deformation potential by longitudinal acoustic phonons (LA-DP), and the piezoelectric effect by both longitudinal acoustic phonons (LA-PZ) and transverse acoustic phonons (TA- PZ). When SO is not included the system is a simple 2-level system, independent of spin. Decay times are studied as a function of both confinement frequency (ω0) and magnetic field (B). Depending on system parameters, either LA-DP or TA-PZ can be the dominant source of decay. When SO is included in the model, the system becomes a four-level system and additional decay channels open due to the additional number of levels in the subspace. In the strong-SO regime the relaxation rates of the single-electron case are reduced by as much as 0.5 ns^−1 and the decoherence rates by as much as 1 ns^−1. In the three-electron QD decay rates are investigated as a function of B. The TA-PZ interaction is primarily investigated as it is found to be the main source of decay for the majority of the B field investigated. Correlation effects on decay rates are isolated from energy effects, revealing that Coulomb-induced correlations between electrons play a significant role in reducing decay rates. We find that for the parameters investigated in this dissertation, SO does not, on average, reduce the peak relaxation rates in the three-electron system, rather it shifts them towards higher magnetic fields.