Abstract
The first lesson presented a general overview of mesoscopic state superpositions in quantum optics. It showed how these superpositions can be generated, either with photons or with atoms. The link with quantum computing was also clarified, by showing that these superpositions can be prepared using logic gates in which one "quantum bit" controls the final state of a large number of target bits. The fragility of these superpositions was also discussed and qualitatively explained using simple physical images. It was shown that mesoscopic superpositions are much more strongly entangled with the environment than classical states, and this result was introduced as a general criterion for defining the classical or non-classical character of a given quantum state a priori.
