The $\hbar\rightarrow 0$ Limit of the Entanglement Entropy

TL;DR

This paper investigates the semi-classical limit of bipartite entanglement entropy in quantum systems, showing it remains finite as Planck's constant approaches zero and relates to classical Shannon entropy for fermions.

Contribution

It explicitly computes the $hrightarrow 0$ limit of entanglement entropy for a 1D quantum system, revealing its finiteness and classical correspondence.

Findings

The entanglement entropy limit is finite as $hrightarrow 0$.

For fermions, the limit matches the Shannon entropy of $N$ bits.

The result bridges quantum entanglement and classical information measures.

Abstract

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 $\hbar\rightarrow 0$ 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 $\hbar\rightarrow 0$ limit of the bipartite entanglement entropy coincides with the Shannon entropy of $N$ bits.