Since the early days of quantum mechanics, the interferences that are apparent between spatially separated trajectories of quantum particles has not ceased to fascinate both professional physicists and the broader public. In this lecture, Prof. Aspect will present results from a series of experiments - each of which has been realized with a single photon (i.e. a single quantum of light) - that serve to emphasize the weirdness of the concept of ‘wave particle duality’, an idea that is at the root of the quantum revolution of the 20th century. The single photon sources used in these experiments have recently left the laboratory, and are now an important resource in the technological domains of quantum information and quantum cryptography.
Prof. Aspect is a giant in the area of experimental tests of fundamental concepts in quantum mechanics using optics. In the early 1980's he performed the elusive ‘Bell test experiments’ that showed Albert Einstein, Boris Podolsky and Nathan Rosen's reductio ad absurdum of quantum mechanics, namely that quantum mechanics implied a ‘ghostly action at a distance’ (the EPR paradox), was neither absurd nor ghostly! That is, the ‘ghostly action at a distance’ that so bothered Einstein appears to be an essential and unavoidable fact of nature that we simply must reconcile ourselves to. These and other experiments performed by Prof. Aspect have contributed enormously to our understanding regarding the true nature of the quantum world, including core ideas and concepts like ‘wave-particle duality’ and ‘quantum entanglement’ that are hot subjects in everything from books popularizing physics to the Big Bang Theory.
Since the early days of quantum mechanics, the interferences that are apparent between spatially separated trajectories of a single particle has not ceased to fascinate both professional physicists and the broader public. In this lecture I will present results from a series of experiments - each of which has been realized with a single photon (i.e. a single quantum of light) - that serve to emphasize the weirdness of the concept of “wave particle duality”, an idea that is at the root of the quantum revolution of the 20th century. The single photon sources used in these experiments have recently left the laboratory, and are now an important resource in the technological domains of quantum information and quantum cryptography.
In the early 1980's, Feynman realized that many-body entangled systems pose an insurmountable challenge to classical computers, and suggested that a promising way to attack the problem is to simulate the situation with an equivalent quantum system (R. P. Feynman, “Simulating physics with computers”, International Journal of Theoretical Physics 21, 467-488 [1982]).
Since the early 2000's, ultra-cold atoms have been found an excellent system to realize Feynman's program, and realize quantum simulators of difficult condensed matter problems, where many electrons are entangled. One can cite the Mott insulator to superconductor transition in a lattice, or the BEC-BCS transition, to name only a few. In our group, we study the problem of quantum particles in a disordered potential, and in particular the celebrated Anderson localization phenomenon, i.e. the total suppression of conductivity beyond a certain level of disorder, a phenomenon impossible to understand in a classical framework. Our experiments use atomic Bose-Einstein Condensates in optical disordered potentials based on laser speckle.
I will describe the Anderson localization phenomenon, present some experimental results that shed a new light on strong and weak localization, and evoke the open problems.