Zero field entanglement in dipolar coupling spin system at negative temperatures

Abstract

A dipolar coupled spin system can achieve internal thermodynamic equilibrium states at negative absolute temperature. We study analytically and numerically the temperature dependence of the concurrence in a dipolar coupled spin-1/2 system in both non-zero and zero fields and show that, at negative temperatures, entangled states can exist even in zero magnetic field.

9 pages, 4 figures International Journal of Quantum Information, 2013