Proton-neutron entanglement in the nuclear shell model

We compute the proton-neutron entanglement entropy in interacting nuclear shell model for a variety of nuclides and interactions. Some results make intuitive sense, example that structure, as governed by single-particle monopole energies, strongly affects energetically available space thus entropy. also find surprising result: at low excitation energy tends to decrease when $N \neq Z$. While we provide evidence this arises from physical force contrasting with random two-body interactions which shows no such decrease, exact mechanism is unclear. Nonetheless, suggests models neutron-rich nuclides, coupling between protons neutrons may be less computationally demanding than one might otherwise expect.