Hai-Bin Liu, Jun-Hong An, Chong Chen, Qing-Jun Tong, Hong-Gang Luo, C. H. Oh
We study the quantum phase transition (QPT) of the sub-Ohmic spin-Boson model (SBM) both with and without the rotating-wave approximation (RWA). It is shown analytically that a novel QPT occurs in the model when the RWA is used. When the RWA is relaxed, after revealing the conventional delocalized-localized QPT in the full range of the power index $s$ of the spectral density, we show that the novel QPT still exists in the delocalized phase regime based on the perturbation method. This QPT causes a dynamical transition of the spin system from complete decoherence to decoherence suppression, which suggests a useful control way to the detrimental effects of the reservoir to the system. Our result also shows that the coherent-incoherent transition extensively studied is caused essentially by the intrinsic QPT of the system.
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http://arxiv.org/abs/1208.4295
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