The hbar→ 0 Limit of the Entanglement Entropy

Entangled quantum states share properties that do not have classical analogs, in particular, they show correlations that can violate Bell inequalities. It is therefore an interesting question to see what happens to entanglement measures - such as the entanglement entropy for a pure state - taking the semi-classical limit, where the naive expectation is that they may become singular or zero. This conclusion is however incorrect. In this paper, we determine the hbar→ 0 limit of the bipartite entanglement entropy for a one-dimensional system of N quantum particles in an external potential and we explicitly show that this limit is finite. Moreover, if the particles are fermionic, we show that the hbar→ 0 limit of the bipartite entanglement entropy coincides with the Shannon entropy of N bits.