At the start of the twentieth century, the first quantum revolution upset our vision of the world. New physics offered surprising realities, such as wave-particle duality, and led to major inventions: the transistor, the laser, and computer's integrated circuits. Less known is the second quantum revolution, arguably initiated in 1935 during a debate between giants Albert Einstein and Niels Bohr. This revolution is still unfolding. Its revolutionaries--including the author of this short accessible book, Nobel Prize-winning physicist Alain Aspect--explore the notion (...) of entangled particles, able to interact at seemingly impossible distances. Aspect has investigated entangled particles since the beginning of the 1980s and has helped to show how entanglement may both upend existing technologies, like cryptography, and usher in entirely new ones, like quantum computing. Explaining this physics of the future, this work tells a story of how philosophical debates can shape new realities. (shrink)

We discuss the question of linear momentum conservation when an atom coupled to a laser field enters into a state which is not an eigenstate of the linear momentum. Such a situation happens in the recently demonstrated laser cooling of atoms by velocity selective coherent population trapping. We show that this process can be understood as a filtering of the atomic state by the laser field taken as a classical measuring apparatus. In a different approach, the laser field can be (...) taken as a quantized system; then the filtering process leads to an “entangled state” of the atom and the field. (shrink)