  In this work, we study strategies for the optical control, within the dipole
approximation, of a qubit encoded in the three-electron states of a triple
quantum dot. The system is described by effective confining potentials, and its
electronic structure by the configuration interaction method. Optimal control
theory (OCT) was applied to design low-fluence time-dependent electric fields
controlling the qubit in times shorter than a nanosecond. The resulting pulses
produce transitions between the qubit states for experimentally available field
amplitudes with high fidelity. Their frequency spectra are related to
transitions to some lower-lying excited states and a simplified pulse based on
those sequential transitions is presented. The limitations of an extended
Hubbard description for the type of strategy analyzed here are also discussed.

Mesoscale and Nanoscale Physics