Quantum Optical Tests of the Foundations of Physics

Abstract

Quantum mechanics began with the solution of the problem of blackbody radiation by Planck's quantum hypothesis: in the interaction of light with matter, energy can only be exchanged between the light in a cavity and the atoms in the walls of the cavity by the discrete amount E = hν, where h is Planck's constant and ν is the frequency of the light. Einstein, in his treatment of the photoelectric effect, reinterpreted this equation to mean that a beam of light consists of particles (“light quanta”) with energy hν. The Compton effect supported this particle viewpoint of light by demonstrating that photons carried momentum, as well as energy. In this way, the wave-particle duality of quanta made its first appearance in connection with the wave-particle duality properties of light. It might seem that the introduction of the concept of the photon as a particle would necessarily also introduce the concept of locality into the quantum world. However, in view of observed violations of Bell's inequalities, exactly the opposite seems to be true. Here we review some recent results in quantum optics which elucidate nonlocality and other fundamental issues in physics. In spite of the successes of quantum electrodynamics, and of the standard model in particle physics, there is still considerable resistance to the concept of the photon as a particle. Many papers have been written trying to explain all semiclassical theoryYoung's two slit experiment, exclusion of optical phenomena semiclassically, i.e., with the light viewed as a classical wave, and the atoms treated quantum mechanically [80.1,2,3,4]. We first present some quantum optics phenomena which exclude this semiclassical viewpoint.