We present measurements of the electron phase coherence time ${\tau }_{\varphi }$ on a wide range of open ballistic quantum dots (QDs) made from InGaAs heterostructures. The observed saturation of ${\tau }_{\varphi }$ below temperatures $0.5\mathrm{K}<T_{\mathrm{onset}}<5\mathrm{K}$ is found to be intrinsic and related to both the size and the openings of the QDs. Combining our results with previous reports on ${\tau }_{\varphi }$ in GaAs QDs, we provide new insight into the long-standing problem of the saturation of ${\tau }_{\varphi }$ in these systems: the dwell time becomes the limiting factor for electron interference effects in QDs at low temperature.

• Received 2 September 2004

DOI:https://doi.org/10.1103/PhysRevLett.94.146802