Spin-boson models provide an interaction between atoms and harmonic oscillators and lie at the heart of quantum science. The superradiant phase transition in the Dicke model  constitutes a prime example of a non-equilibrium phase transition which has recently been realized experimentally . In addition to these steady-state phases, we observe a second dissipative phase transition to a nonstationary phase, which can be understood as a breakdown of the photon blockade which is known from the single-particle context . We demonstrate that our many-body breakdown effect is of cooperative nature and study its dependence on the system size . The model can be realized using experimental platforms, such as trapped ions or neutral atoms.  R. H. Dicke, Phys. Rev. 93, 99 (1954); K. Hepp and E. H. Lieb, Ann. Phys. 76, 360 (1973); Y. K. Wang and F. T. Hioe, Phys. Rev. A 7, 831 (1973).  K. Baumann et al., Nature 464, 1301 (2010); Z. Zhiqiang et al., Optica 4, 424 (2017).  H. J. Carmichael, Phys. Rev. X 5, 031028 (2015); J. Fink et al., Phys. Rev. X 7, 011012 (2017)  F. Reiter, T. L. Nguyen, J. P. Home, and S. F. Yelin, arXiv: 1807.06026 (2018).
Florentin Reiter / Harvard Univeristy
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