2005/06/24 by J. G. Brankov, Brankov, J. G., N. S. Tonchev +3
Physics and Astronomy · #FOS: Physical sciences #Quantum Physics (quant-ph) #quant-ph
paper · pdf · doi:10.48550/arxiv.quant-ph/0506207
5 pages, no figures
arxiv created 2005/06/24 · arxiv updated 2009/12/01
In this Comment we show that the temperature-dependent effective Hamiltonian derived by Reslen \it et al [Europhys. Lett., \bf 69 (2005) 8] or that one by Liberti and Zaffino [arXiv:cond-mat/0503742] for the Dicke model cannot be correct for any temperature. They both violate a rigorous result. The former is correct only in the quantum (zero-temperature) limit while the last one only in the classical (infinite temperature) limit. The fact that the Dicke model belongs to the universality class of the infinitely coordinated transverse-field XY model is known for more then 30 years.