The dipole-coupled two-level atoms (qubits) in a single-mode resonant cavity are studied by extended bosonic coherent states. The numerical solution is presented. The first-order quantum phase transitions may occur in finite systems, in contrast to the original Dicke model. This system also exhibits a second-order quantum phase transition from the normal to the superradiant phase, as in the original Dicke model. Finite-size scaling for several observables—such as average fidelity susceptibility, order parameter, and concurrence—is performed for different interatomic interactions. The scaling exponents obtained suggest that interatomic interactions do not change the universality class.

• Received 16 August 2010

DOI:https://doi.org/10.1103/PhysRevA.82.053841