  A two-dimensional system of atoms in an anisotropic optical lattice is
studied theoretically. If the system is finite in one direction, it is shown to
exhibit a transition between a two-dimensional superfluid and a one-dimensional
Mott insulating chain of superfluid tubes. Monte Carlo simulations are
consistent with the expectation that the phase transition is of
Kosterlitz-Thouless type. The effect of the transition on experimental
time-of-flight images is discussed.
