  We present results of numerical simulations of the 2+1d Nambu -- Jona-Lasinio
model with non-zero baryon chemical potential mu and spatially-varying complex
diquark source strength j. By choosing arg(j) to vary smoothly through 2 pi
across the spatial extent of the lattice, a baryon number current is induced
which in the high density phase remains non-vanishing as |j|->0; we are hence
able to extract a quantity characteristic of a superfluid known as the helicity
modulus. We also study supercurrent flow at non-zero temperature and estimate
the critical temperature at which the normal phase is restored, which is
consistent with the conventional picture for thin-film superfluids in which the
transition is viewed in terms of vortex -- anti-vortex unbinding.
