Spin and occupation number entanglement of Dirac fields for noninertial observers

We investigate the Unruh effect on entanglement taking into account the spin degree of freedom of the Dirac field. We analyze spin Bell states in this setting, obtaining their entanglement dependence on the acceleration of one of the partners. Then, we consider simple analogs to the occupation number entangled state vertical bar 00 > + vertical bar 11 > but with spin quantum numbers for vertical bar 11 >. We show that, despite their apparent similitude, while the spinless case is always qubit X qubit, for the spin case acceleration produces a qubit X four-level quantum system state. We also introduce a procedure to consistently erase the spin information from our setting preserving occupation numbers. We show how the maximally entangled state for occupation number emerges from our setting. We as well analyze its entanglement dependence on acceleration, obtaining greater entanglement degradation than in the spinless case.