Particle partitioning entanglement in itinerant many-particle systems

For itinerant fermionic and bosonic systems, we study particle entanglement, defined as the entanglement between two subsets of particles making up the system. We formulate the general structure of particle entanglement in many-fermion ground states, analogous to the area law for the more usually studied entanglement between spatial regions. Basic properties of particle entanglement are uncovered by considering relatively simple itinerant models.