Dephasing of electrons by two-level defects in quantum dots

The electron dephasing time ${\tau }_{\phi }$ in a diffusive quantum dot is calculated by considering the interaction between the electron and dynamical defects, modeled as two level systems. Using the standard tunneling model of glasses, we obtain a linear temperature dependence of $1/{\tau }_{\phi },$ consistent with the experimental observation. However, we find that, in order to obtain dephasing times on the order of nanoseconds, the number of two-level defects needs to be substantially larger than the typical concentration in glasses. We also find a finite system-size dependence of ${\tau }_{\phi },$ which can be used to probe the effectiveness of surface-aggregated defects.