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Comment on equivalence between quantum phase transition phenomena in radiation-matter and magnetic systems

J. G. Brankov·N. S. Tonchev·V. A. Zagrebnov
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Abstract

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.

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J. G. Brankov, N. S. Tonchev, V. A. Zagrebnov. 2005-06-24. Comment on equivalence between quantum phase transition phenomena in radiation-matter and magnetic systems. https://arxiv.org/abs/quant-ph/0506207

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