The generation and the characterization of multipartite entangled light is an important and challenging task in quantum optics. In this paper the entanglement properties of the light emitted from a planar semiconductor microcavity are studied. The intracavity scattering dynamics leads to the emission of light that is described by a four-partite
W state. Its multipartite correlations are identified by using the method of entanglement witnesses. Entanglement conditions are derived, which are based on a general witness constructed from
W states. The results can be used to detect entanglement of light that propagates through lossy and even turbulent media.
For the interaction of two entangled atoms with the two-mode squeezed light field,the entanglements between the atom with the light field and that between the two-modes of the light field are studied.Setting that one atom is outside the cavity and the other atom enters the cavity to interact with the light field,generally the entanglement changes periodically and the period is not affected by the rotation angle of the outside atom and the phase difference in the atomic entangled state.But,if the squeezing parameter of the light field and the rotation angle of the atom outside the cavity satisfy a certain relation,atom and the light field will be disentangled forever.
By considering vibrational heating of an intracavity trapped ion and cavity damping, we investigate the effects of decoherence on entanglement and two-mode squeezing of output light from the cavity when the ion is excited continuously. It is found that the bright output light with the steady robust entanglement can be always achieved even in the presence of decoherence. Moreover, the entangled output light may not exhibit two-mode squeezing because the heating of the vibrational mode has stronger limitation on the two-mode squeezing than on the entanglement of the output light.