Introduction to single-particle control and history of early research developments leading to this work at ENS.
Summary
The first introductory lesson began by recalling the quotation from the Swedish Academy of Sciences, which drew a parallel between the research carried out in Paris on the non-destructive manipulation and control of photons trapped in a cavity and that carried out in Boulder on the study of trapped ions. The quote also made it clear that these experiments had long been considered practically impossible. In commenting on this quotation, it seemed appropriate to link this work to the thought experiments imagined by the founders of the theory at the beginning of the XXᵉ century and to explain how these experiments became feasible thanks to advances in technologies all derived from quantum physics.
The lesson began by recalling how the concept of the photon was born in 1905 in Einstein's seminal paper on the photoelectric effect. The hypothesis that light, classically considered as a wave, should also be described as a set of discrete particles, the photons, was to revolutionize physics by introducing the notion of dualism between waves and particles, which de Broglie was to extend to matter some twenty years later. This duality was later formalized in the quantum theory elaborated by Heisenberg, Schrödinger and Dirac, in the form of the principle of superposition of states, which states that a quantum system potentially exists in several states at once, suspended as it were between different classical realities. To understand the significance of this principle, and of wave-particle dualism, Bohr and Einstein, during the Solvay congresses of 1927 and 1930, described thought experiments that have become famous. These included the Young's slit experiment, with a moving slit designed to "spy" on the path followed by a particle passing through the apparatus, and the "photon box" experiment, designed to count the photons contained in a box without destroying them, and to determine precisely when these photons escape. The lesson took up the description of these experiments, explaining how they illustrated Bohr's principle of complementarity. This principle analyzes waves and particles not as contradictory entities, but as complementary notions, one or the other manifesting itself according to the nature of the experiments performed. Special attention was paid to Schrödinger's famous cat, suspended between life and death, another thought experiment devised by the Austrian physicist to highlight the interpretive problem facing quantum physics when trying to understand the transition between the microscopic world, where the principle of superposition applies, and the macroscopic world, where its effects are almost never seen directly.
