Macroscopic thermal entanglement

We review recent results on the existence and use of entanglement in macroscopic systems at finite temperatures. Entanglement represents a particular quantum form of correlations and we explore the relevance of these correlations on thermodynamic properties of macroscopic systems, as well as its survival at finite temperatures. Various lower bounds for the entanglement temperature (the temperature below which entanglement surely exists in a system) are discussed and it is shown that, in some cases, macroscopic entanglement can exist even at room temperatures. Furthermore, the relevant correlations determining the macroscopic behavior of some systems are present due to entanglement only, as we show in the example of high-temperature superconductivity. Entanglement can also affect various thermodynamic properties, such as magnetic susceptibility, internal energy and pressure. Motivated by the fact that entanglement is a crucial resource for quantum information processing, we also discuss how to extract it from macroscopic systems, namely from spin-chains. Finally, we illustrate the generation and manipulation of entanglement in a macroscopic system of non-interacting hopping bosons.