Characterizing and quantifying entanglement of quantum states in
many-particle
systems is at the core of a full understanding of the nature of quantum
phase
transitions in matter. Entanglement is a relative notion and, although
many
measures of entanglement have been defined in the literature, assessing
the
utility of those measures to characterize quantum phase transitions is
still
an open problem.
In this seminar I will show how our concept of Generalized Entanglement
[1], a
notion of entanglement that is observer-dependent and goes beyond the
usual
subsystem decomposition, succesfully characterizes different types of
broken-symmetry quantum phase transitions. In particular, we will apply
this
concept to the Ising model in a transverse magnetic field and the
Lipkin-Meshkov-Glick model [2].
[1] H. Barnum, E. Knill, G. Ortiz, L. Viola (2002), PRA v.68 p.032308
(2003).
[2] R. Somma, G. Ortiz, H. Barnum, E. Knill, L. Viola (2004),
quant-ph/0403035
(PRA in press).