Quantum Optics

It is well known that electromagnetic fields are important probes of the properties of matter. We can learn about atomic molecular energy levels by studying the absorption, emission, and scattering of electromagnetic waves. For example, the rate at which a system absorbs energy and its dependence on the frequency of the electromagnetic field gives information on the allowed transitions. From such studies one can determine the energy levels and their lifetimes. Similarly, scattering processes provide a wealth of information. The traditional probing of matter is restricted to weak fields; however, in Chapter 11 we saw how strong fields dress the energy levels of a system. Strong fields also modify the transition rates. In order to study the characteristics of such modifications we need to probe a coherently driven system using a probe field. In this chapter we study the absorption, emission, and scattering processes in strongly driven systems. A novel characteristic of radiation from strongly driven systems is its nonclassical nature.

Effects of relaxation: optical Bloch equations

So far we have considered only interactions with external electromagnetic fields. In reality, one has to account for various sources of decay of the atomic population and coherences. For example, an atom can decay radiatively by emitting a photon. The resulting collisions change the populations and coherences. In Chapter 9 we discussed in detail how various relaxation processes can be included from first principles in the master equation framework.