Atom-Field Entanglement in a Cavity QED System

We consider the entanglement in a cavity QED system as a function of driving field strength via the entanglement of formation and the logarithmic negativity. There is an optimal field strength for generating entanglement, around the saturation intensity. When the atoms become saturated, the system tends towards a product state where the field is in a coherent state. We also consider conditioned homodyne and conditioned photo as entanglement witnesses. Further we consider the time development of entanglement, and the amount of information about entanglement contained in time dependent cross correlation functions.