Weak Localisation of Light by Atoms with Quantum Internal Structure

As a commonplace, we could say that all simple problems in physics have been solved a long time ago, and that we are tempted to turn to the challenging field called, rather pompously, “wave transport in complex systems”. Here, “wave” is meant to emphasize the influence of interference (which is truly quantum mechanical for massive particles like electrons or atoms). “Transport” implies that we are interested in situations out of ther- modynamic equilibrium (but not too far, so that linear response theory applies). Finally, a system will be called “complex” whenever it is disordered, or strongly interacting, or chaotic. Our choice of this field is motivated by two aspects: on the side of applied physics, all remote sensing techniques need to incorporate the multiple scattering of waves in turbid media, and the miniaturisation process in semi-conductor industry arrives at length scales where the control of quantum interference becomes crucial. On the academic side of more fundamental physics, we would like to understand and enjoy the predictive power of the best physical theory available today: quantum theory.