Ground state factorization and correlations with broken symmetry

We show how the phenomenon of factorization in a quantum many body system is of collective nature. To this aim we study the quantum discord $Q$ in the one dimensional XY model in a transverse field. We analyze the behavior of $Q$ at both the critical point and at the non critical factorizing field. The factorization is found to be governed by an exponential scaling law for $Q$. We also address the thermal effects fanning out from the anomalies occurring at zero temperature. Close to the quantum phase transition, $Q$ exhibits a finite-temperature crossover with universal scaling behavior, while the factorization phenomenon results in a non trivial pattern of correlations present at low temperature.

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