  We study decoherence of a quantum dot charge qubit due to coupling to
piezoelectric acoustic phonons in the Born-Markov approximation. After
including appropriate form factors, we find that phonon decoherence rates are
one to two orders of magnitude weaker than was previously predicted. We
calculate the dependence of the Q-factor on lattice temperature, quantum dot
size, and interdot coupling. Our results suggest that mechanisms other than
phonon decoherence play a more significant role in current experimental setups.
