The frustration-free fully packed loop model

We consider a quantum fully packed loop model on the square lattice with frustration-free projector Hamiltonian and ring-exchange interactions acting plaquettes. A boundary is added to favour domain-wall conditions link ground state properties combinatorics six-vertex literature. discuss how term fractures Hilbert space into Krylov subspaces, we prove that ergodic within each subspace, leading series of energy-equidistant exact eigenstates in lower end spectrum. Among them systematically classify both finitely entangled product eigenstates. Using recursion relation for enumerating half-plane configurations, compute numerically entanglement entropy state, confirming area law scaling. Finally, spectrum shown be gapless thermodynamic limit trial constructed by adding twist superposition.