Non-linear spectroscopy using quantum photons: Make Photons Quantum Again!

Recent advances in both theory and experimental technique have advanced the notion that there might be something to be gained by probing material systems with quantum photons, as opposed to more conventional laser sources.   First, I shall discuss a couple of recent experiments that demonstrate that one can in fact extract ultrafast (fs) time-scale dynamics using CW sources and our theoretical methods for computing such responses. I shall propose that exciton/exciton correlations lead to the production of entangled photons.  By measuring the entanglement entropy, one has a direct measure of both the magnitude and time-scale of such correlations.