Coupled quantum rotor chain
= Coupled quantum rotor chain
{title2=$H=\sum_n[\ell_n^2/(2I)-J\cos(\phi_{n+1}-\phi_n)]$}
A chain with local rotor inertia and a phase-locking interaction $-J\cos(\phi_{n+1}-\phi_n)$. Its smooth-phase limit is an elastic phase field with inertia $I$ and stiffness $J$. Compact winding and phase-slip processes remain part of the full model even when absent from the Gaussian smooth-sector approximation.