Superposition states of ultracold bosons in rotating rings with a realistic potential barrier

In a recent paper [Phys. Rev. A 82, 063623 (2010)] Hallwood et al. argued that it is feasible to create large superposition states with strongly interacting bosons in rotating rings. Here we investigate in detail how the superposition states in rotating-ring lattices depend on interaction strength and barrier height. With respect to the latter we find a trade-off between large energy gaps and high cat quality. Most importantly, we go beyond the \delta-function approximation for the barrier potential and show that the energy gap decreases exponentially with the number of particles for weak barrier potentials of finite width. These are crucial issues in the design of experiments to realize superposition states.