  We consider an atom (represented by a two-level system) moving in front of a
dielectric plate, and study how traces of dissipation and decoherence (both
effects induced by vacuum field fluctuations) can be found in the corrections
to the unitary geometric phase accumulated by the atom. We consider the
particle to follow a classical, macroscopically-fixed trajectory and integrate
over the vacuum field and the microscopic degrees of freedom of both the plate
and the particle in order to calculate friction effects. We compute
analytically and numerically the non-unitary geometric phase for the moving
qubit under the presence of the quantum vacuum field and the dielectric mirror.
We find a velocity dependence in the correction to the unitary geometric phase
due to quantum frictional effects. We also show in which cases decoherence
effects could, in principle, be controlled in order to perform a measurement of
the geometric phase using standard procedures as Ramsey-like interferometry.
