Universality in volume law entanglement of pure quantum states

Understand

A pure quantum state can fully describe thermal equilibrium as long as one focuses on local observables.

• Thermodynamic entropy can also be recovered as the entanglement entropy of small subsystems.
• When the size of the subsystem increases, however, quantum correlations break the correspondence and cause a correction to this simple volume-law.
• To elucidate the size dependence of the entanglement entropy is of essential importance in linking quantum physics with thermodynamics, and in addressing recent experiments in ultra-cold atoms.