Quantum optics overview

The second lesson recalled the principles of quantum optics. It is indeed in this field that coherent mesoscopic superpositions have been most convincingly studied and prepared, and it is therefore very useful to understand the general concepts of quantum optics in order to study these superpositions. The lesson began with a reminder of the description of a field in terms of photons, based on the analogy between a radiation mode and a harmonic oscillator. The main observables of the field (photon number, quadratures) were described, as well as some important states, including Fock and coherent states. The latter play an essential role in the study of the classical-quantum limit. These are the quantum states that correspond to the most classical possible image of an oscillator. They are also the states that are naturally prepared when a quantum mode is coupled to a classical current. We have recalled in detail the essential properties of these states. We also described their superpositions, generally referred to in quantum optics as "Schrödinger cat" states, in reference to the famous metaphor with which this physicist first introduced the problem of macroscopic superpositions into a physical discussion. The lesson ended with a quick reminder of the description of atom-matter coupling, which plays an essential role in the processes of field generation and detection.