Polaritonic characteristics of insulator and superfluid phases in a coupled cavity array

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  • 23 July 2007
Abstract
Recent studies of quantum phase transitions in coupled atom-cavity arrays have focused on the similarities between such systems and the Bose-Hubbard model. However, the bipartite nature of the atom-cavity systems that make up the array introduces some unique features. The detuning between the atoms and the cavity field provides an additional parameter, which affects the interaction between the sites as well as the nature of the fundamental excitations of the system. Two species of polaritons appear, which may behave as atoms, as photons, or as highly entangled atom-photon states. In order to examine these differences, the behavior of a simple two-site model is studied over a wide range of values for the detuning and the hopping strength, using two order parameters. The variance of the total excitation number distinguishes insulator and superfluid phases, while the polaritonic character of the ground state is measured by the degree of symmetry between the two species. Six distinct regions are identified, in which the ground state of the system behaves as a polaritonic insulator, a photonic superfluid, an atomic insulator, or a polaritonic superfluid.

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