Entanglement entropy in extended quantum systems

After a brief introduction to the concept of entanglement in quantum systems, I apply these ideas to many-body systems and show that the von Neumann entropy is an effective way of characterising the entanglement between the degrees of freedom in different regions of space. Close to a quantum phase transition it has universal features which serve as a diagnostic of such phenomena. In the second part I consider the unitary time evolution of such systems following a 'quantum quench' in which a parameter in the Hamiltonian is suddenly changed, and argue that finite regions should effectively thermalise at late times, after interesting transient effects.