Cavity QED for entanglement in atomic and photonic systems

In free space, the interaction between a single photon and single atom is relatively weak, while the interaction between two photons is completely negligible. A cavity can be used to substantially enhance the interaction between a single photon and a single atom, up to the point where the coherent coupling between the photon and the atom dominates over the dissipative couplings of the photon and the atom to the environment. Even stronger coherent coupling can be achieved with atomic ensembles in cavities. I will discuss how the atom-cavity coupling can generate strong nonlinearities that can be used to entangle photons with atoms, photons with photons, or atoms with atoms, for a variety of applications. The latter include quantum measurements beyond the Standard Quantum Limit with atomic clocks and interferometers, photonic quantum gates, optical quantum networks, atomic quantum memories, single-photon transistors, and generally the field of strongly nonlinear quantum optics.