Dephasing in an isolated double-quantum-dot system deduced from single-electron polarization measurements

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Abstract
We report measurements of single-electron polarization in a coupled double-quantum-dot device isolated from current probes and demonstrate that the energetics observed for this process differs from that observed in double dots coupled to reservoirs. The movement of the electrons is detected by a quantum point contact. By analyzing the energy broadening corresponding to the tunneling of a single electron from one dot to the other we estimate a minimum for the intradot scattering time to be 0.2 ns. This energy broadening follows the predicted shot-noise variation in the detector with gate voltage, but is three orders-of-magnitude higher. We speculate that two-level systems could account for the discrepancy.