Quantifying entanglement in macroscopic systems.

Traditionally, entanglement was considered to be a quirk of microscopic objects that defied a common-sense explanation. Now, however, entanglement is recognized to be ubiquitous and robust. With the realization that entanglement can occur in macroscopic systems - and with the development of experiments aimed at exploiting this fact - new tools are required to define and quantify entanglement beyond the original microscopic framework.