Dephasing in Open Quantum Dots

Shape-averaged magnetoconductance (weak localization) is used for the first time to obtain the electron phase coherence time $\tau_{\phi}$ in open ballistic GaAs quantum dots. Values for $\tau_{\phi}$ in the range of temperature T from 0.335 to 4 K are found to be independent of dot area, and are not consistent with the $\tau_{\phi} \propto T^{-2}$ behavior expected for isolated dots. Surprisingly, $\tau_{\phi}(T)$ agrees quantitatively with the predicted dephasing time for disordered two-dimensional electron systems.