  The effects resulting due to dressing of an exciton with phonons are analysed
as the source of unavoidable decoherence of orbital degrees of freedom in
quantum dots. The dressing with longitudinal optical phonons results in
energetic shift of order of a few meV even of the ground state of exciton in a
state-of-the-art InAs/GaAs dot and the mediating role of longitudinal
acoustical phonons is essential in this process. The characteristic time needed
for dressing of the exciton with optical phonons is of a picosecond order. That
time can be regarded as the lowest limit for decoherence for optically driven
quantum gates employing self-assembled quantum dot structures.
