Optical Bloch equations

Until now, our discussion has primarily been about closed quantum systems, which evolve unitarily. Specifically, we considered single and multiple component systems, such as atoms and photons, but we kept every part, and never threw anything away. However, in real systems, we often want to be able to disregard certain microscopic dynamics, or do not have access to certain parts of a system. For example, we may want to cool an atom, but will not keep track of the microscopic state of the cooling laser beam after it has interacted with the atom. Or an atom may interact with the vacuum, emitting a photon which we do not track. The study of such topics is the subject of open quantum system dynamics. This chapter begins our investigation of open quantum systems, with the goal of developing a fully quantum-mechanical model of an atom undergoing spontaneous emission, while interacting with a classical electromagnetic field.

• Derivation of the optical Bloch equations
• Steady-state limits of the optical Bloch equations

Handouts

• Derivation of the optical Bloch equations
• Solutions: transient and steady state
• Unraveling quantum open system dynamics
• Also see API p. 369, on Absorbed energy