Thermal entanglement in the nanotubular system Na2V3O7

Macroscopic entanglement witnesses have been put forward recently to reveal nonlocal quantum correlations between individual constituents of the solid at nonzero temperatures. Here we apply a recently proposed universal entanglement witness, the magnetic susceptibility [New J. Phys. 7, 258 (2005)] for the estimation of the critical temperature T-c in the nanotubular system Na2V3O7 below which thermal entanglement is present. As a result of an analysis based on the experimental data for dc-magnetic susceptibility, we show that T-c approximate to 365 K, which is approximately three times higher than the critical temperature corresponding to the bipartite entanglement.