Pourquoi la physique quantique ?

Why did scientists at the beginning of the 20th century need to develop a new physical theory? What are the characteristics of this quantum theory? Asking these questions is increasingly important today because quantum technologies are taking on a growing role in our daily lives. In order to understand the concepts of wave-particle duality, photoelectric effect, or simply the word "quantum", we will present various experiments: the Michelson interferometer will introduce the notion of interference and light phase; the presentation of the photoelectric effect will be an opportunity to discuss the quantization of energy exchanges between light and matter. We will conclude our journey by discussing light polarization and quantum state control.