  Ultracold bosons in rotating ring lattices have previously been shown to form
macroscopic superpositions of different quasi-momentum states. We demonstrate
that the generation of such kind of states using slightly non-uniform ring
lattices has several advantages: the energy gap decreases less severely with
the number of particles, the sensitivity to detunings from the critical
rotation frequency is reduced, and the scheme is not limited to commensurate
filling. We show that different quasi-momentum states can be distinguished in
time-of-flight absorption imaging and propose to probe correlations via the
many-body oscillations induced by a sudden change in the rotation frequency.
