Non-adiabatic Quantum Control of a Semiconductor Charge Qubit

A GaAs double quantum dot is configured in the single-electron regime and operated as a charge qubit. The two basis states correspond to the electron being in either the left or the right dot. Non-adiabatic voltage pulses are applied to the depletion gates to drive coherent rotations, and the double dot occupation is read out using a nearby quantum point contact charge sensor. In contrast with previous work, where a single non-adiabatic pulse was applied for quantum control, we apply multiple pulses working towards a charge echo.[1,2] Data for $\frac{\pi}{2}$ - $\tau$ - $\frac{\pi}{2}$ and the $\frac{\pi}{2}$ - $\tau_1$ - $\pi$ - $\tau_2$ - $\frac{\pi}{2}$ ``charge echo" pulse sequences are obtained and compared with numerical simulations of the charge qubit evolution. \noindent References:\\ \noindent [1] K. D. Petersson \textit{et al.}, Phys. Rev. Lett. (in press).\\ \noindent [2] Y. Nakamura \textit{et al.}, Phys. Rev. Lett. {\bf88}, 047901 (2002).\\