  An analogy between the twisted quantum xxz model and a gated Josephson
junction array is used to predict sharp structure in the critical currents
versus gate voltage, and fractional AC Josephson frequencies. We prove
selection rules for level crossings which imply fractional periodicities of
ground states with varying Aharonov-Bohm flux. Extrapolated numerical
diagonalization on ladders, find a Haldane gap at moderate easy-plane
anisotropy, with vanishing superfluid stiffness. Physical parameters for
experimental realization of these novel effects are proposed.
