  We study the spatial decoherence dynamics for the relative position of two
atoms in a singlemode ring cavity. We find that the spatial decoherence of the
two atoms depends strongly on their relative position. Taking into account the
spatial degrees of freedom, we investigate the entanglement dynamics of the
internal states of the two atoms. It is shown that the entanglement decays to
almost zero in a finite time, and the disentanglement time depends on the width
of the wave packets describing the atomic spatial distribution.
