We report on a study of the dynamics of decoherence of a matter-wave
interferometer, consisting of a pair of low-dimensional cold atom condensates
at finite temperature. We identify two distinct regimes in the time dependence
of the coherence factor of the interferometer: quantum and classical. Explicit
analytical results are obtained in both regimes. In particular, in the
two-dimensional (2D) case in the classical (long time) regime, we find that the
dynamics of decoherence is universal, exhibiting a power-law decay with an
exponent, proportional to the ratio of the temperature to the
Kosterlitz-Thouless temperature of a single 2D condensate. In the
one-dimensional (1D) case in the classical regime we find a universal
nonanalytic time dependence of decoherence, which is a consequence of the
nonhydrodynamic nature of damping in 1D liquids.Comment: 4 pages, published versio