Quantum phase transitions in the spin-boson model without the counterrotating terms
Abstract
We study the spin-boson model without the counterrotating terms by a numerically exact method based on variational matrix product states. Surprisingly, the second-order quantum phase transition (QPT) is observed for the sub-Ohmic bath in the rotating-wave approximations. Moreover, first-order QPTs can also appear before the critical points. With the decrease of the bath exponents, these first-order QPTs disappear successively, while the second-order QPT remains robust. The second-order QPT is further confirmed by multi-coherent-states variational studies, while the first-order QPT is corroborated with the exact diagonalization in the truncated Hilbert space. Extension to the Ohmic bath is also performed, and many first-order QPTs appear successively in a wide coupling regime, in contrast to previous findings. The previous pictures for many physical phenomena for the spin-boson model in the rotating-wave approximation have to be modified at least at the strong coupling.
Cite
@article{arxiv.1812.03758,
title = {Quantum phase transitions in the spin-boson model without the counterrotating terms},
author = {Yan-Zhi Wang and Shu He and Liwei Duan and Qing-Hu Chen},
journal= {arXiv preprint arXiv:1812.03758},
year = {2019}
}
Comments
10 pages, 10 figures