  We introduced an elevated trap technique and exploited it for lowering the
effective temperature of indirect excitons. We observed narrow
photoluminescence lines which correspond to the emission of individual states
of indirect excitons in a disorder potential. We studied the effect of
exciton-exciton interaction on the localized and delocalized exciton states and
found that the homogeneous line broadening increases with density and dominates
the linewidth at high densities.
