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Center for Nonlinear Studies |
Questions about the collective behaviour of large numbers of atoms (or artificial atoms) interacting with radiation have a long history, dating back at least to the work of Dicke in 1954. A particularly notable result is that above a critical coupling strength, the ground state of the Dicke model is predicted to become one with a non-zero photon number. However, complications arise from when the diamagnetic coupling (the A^2 term) between light and matter is included, suggesting that the Dicke phase transition may be an unobservable artifact. Nonetheless, in 2010, this transition was observed [1] in a system of cold atoms in an optical cavity, where a generalised Dicke model arises as the effective description of this non-equilibrium problem.
Following a brief review of the history of problems of phase transitions in coupled matter-light systems, I will discuss examples of collective behaviour in systems of cold atoms [2] and superconducting qubits [3]. These will illustrate various different approaches to pumping and decay, and illustrate the similarities and differences between the equilibrium phase diagram and the dynamical phase diagram of these non-equilibrium systems.
[1] K. Baumann, C. Guerlin, F. Brennecke and T. Esslinger, Nature 464, 1301 (2010)
[2] J. Keeling, M. J. Bhaseen and B. D. Simons, Phys. Rev. Lett 105 043001 (2010); M. J. Bhaseen, J. Mayoh, B. D. Simons and J. Keeling, Phys. Rev. A 85, 013817 (2012).
[3] F. Nissen, S. Schmidt, M. Biondi, G. Blatter, H. E. Türeci, and J. Keeling, Phys. Rev. Lett. 110 203602 (2012)
Host: Adolfo del Campo