Entanglement of a cavity field interacting with a superconducting charge qubit

The system of a superconducting charge qubit interacting with a field in the case of lifting the restriction of the degeneracy point (n_g = 1/2 ) is considered. Two different kinds of canonical transformation are used to transform the Hamiltonian of this system into the Jaynes-Cummings model. We use the coherence angle of the qubit coherent state to examine the effects of lifting the restriction of the degeneracy point on the qubit inversion. This helps us to see the variation in the collapse and revival phenomenon. Meanwhile, we also consider the degree of entanglement using the definition of purity, in addition to a discussion on the variance and entropy squeezingt.