Thursday, 08 September, 2011
Superradiant Phase Transitions and the Standard Description of Circuit QED
O. Viehmann, J. v. Delft, and F. Marquardt -
Phys. Rev. Lett., Vol. 107 (11), 113602 (2011)
We investigate the equilibrium behavior of a superconducting circuit QED system containing a large number of artificial atoms. It is shown that the currently accepted standard description of circuit QED via an effective model fails in an important aspect: it predicts the possibility of a superradiant phase transition, even though a full microscopic treatment reveals that a no-go theorem for such phase transitions known from cavity QED applies to circuit QED systems as well. We generalize the no-go theorem to the case of (artificial) atoms with many energy levels and thus make it more applicable for realistic cavity or circuit QED systems.