  Quantum confinement, magnetic-field effects, and laser coupling with the two
low-lying states of electrons bound to donor impurities in semiconductors may
be used to coherently manipulate the two-level donor system in order to
establish the appropriate operational conditions of basic quantum bits (qubits)
for solid-state based quantum computers. Here we present a detailed theoretical
calculation of the damped Rabi oscillations and time evolution of the 1s and
2p+ donor states in bulk GaAs under an external magnetic field and in the
presence of terahertz laser radiation, and their influence on the measured
photocurrent. We also detail the possible experimental conditions under which
decoherence is weak and qubit operations are efficiently controlled.
