Coherent manipulation of a single charge in an isolated double quantum dot

The key requirement that a quantum computer needs to be scalable has motivated recent work demonstrating coherent control of two-level systems in semiconductor devices.\footnote{J. R. Petta et al., Science 309, 2180 (2005).} One very simple semiconductor two-level system is the `charge qubit' in which a single excess electron occupies either the left or right dot of a tunnel-coupled double quantum dot.\footnote{T. Hayashi et al., Phys Rev. Lett. 91, 226804 (2003).} In this work we establish coherent control of an isolated and tunable double dot containing a single electron. The qubit is manipulated by applying non-adiabatic voltage pulses to the surface gate electrodes. State readout is then performed non-invasively using a proximal quantum point contact charge detector.\footnote{M. Field et al., Phys Rev. Lett. 70, 1311 (1993).} We also perform microwave spectroscopy to verify that the frequency of the observed oscillations is consistent with the tunnel coupling strength. This isolated qubit provides a very fundamental system with which to study quantum coherence in semiconductor devices.