title: Ground-state entanglement of the BCS model.
abstract: The concept of local concurrence is used to quantify the entanglement between a single qubit and the remainder of a multiqubit system. For the ground state of the BCS model in the thermodynamic limit the set of local concurrences completely describes the entanglement. As a measure for the entanglement of the full system we investigate the average local concurrence (ALC). We find that the ALC satisfies a simple relation with the order parameter. We then show that for finite systems with a fixed particle number, a relation between the ALC and the condensation energy exposes a threshold coupling. Below the threshold, entanglement measures besides the ALC are significant.
authors.affiliation: Centre for Mathematical Physics, School of Physical Sciences, The University of Queensland, Brisbane 4072, Australia.
authors.forename: Clare
authors.initials: C
authors.lastname: Dunning
authors.forename: Jon
authors.initials: J
authors.lastname: Links
authors.forename: Huan-Qiang
authors.initials: HQ
authors.lastname: Zhou