Global entanglement and quantum criticality in spin chains

The entanglement of quantum $XY$ spin chains of arbitrary length is investigated via a recently developed global measure suitable for generic quantum many-body systems. This entanglement is determined over the phase diagram and found to exhibit rich structure. In particular, the field derivative of the entanglement density becomes singular along the critical line. The form of this singularity is dictated by the universality class controlling the quantum phase transition.