Quantum field, interference, and entanglement effects in nonlinear optical spectroscopy

Experimental observables in quantum systems may be represented by Liouville space pathways which describe the evolving density matrix. The pathways of coupled degrees of freedom may become entangled leading to interesting interference effects. We demonstrate and classify signatures of these quantum effects in optical measurements which involve both classical and quantum modes of the radiation field. Generalized response functions recast in terms of superoperators are used to provide a compact unified description of a broad range of measurements. We discuss interferences of quantum pathways of matter related to the entanglement of excitons in chromophore aggregates, and how they can be manipulated by interactions with quantum optical fields.