We present a new scheme for rotations of a charge qubit associated with a
singly ionized pair of donor atoms in a semiconductor host. The logical states
of such a qubit proposed recently by Hollenberg et al. are defined by the
lowest two energy states of the remaining valence electron localized around one
or another donor. We show that an electron located initially at one donor site
can be transferred to another donor site via an auxiliary molecular level
formed upon the hybridization of the excited states of two donors. The electron
transfer is driven by a single resonant microwave pulse in the case that the
energies of the lowest donor states coincide or two resonant pulses in the case
that they differ from each other. Depending on the pulse parameters, various
one-qubit operations, including the phase gate, the NOT gate, and the Hadamard
gate, can be realized in short times. Decoherence of an electron due to the
interaction with acoustic phonons is analyzed and shown to be weak enough for
coherent qubit manipulation being possible, at least in the proof-of-principle
experiments on one-qubit devices.Comment: Extended version of cond-mat/0411605 with detailed discussion of
phonon-induced decoherence including dephasing and relaxation; to be
published in JET