June 2015: Building on previous results at CNRS, one of the experimental teams at LENS has measured the mobility edge for Anderson localization using ultracold, non-interacting atoms in 3D disorder created with laser speckles. The mobility edge is a key property of a disordered system, since it is the critical energy separating localized states and extended, diffusive states. It is very hard to measure or even to calculate numerically.
The challenge has been overcome using a novel strategy based on the preparation of deeply localized samples and on their successive excitation towards the mobility edge via a periodic modulation of the disorder strength.
This result is based on numerically-calculated spectral functions. An ongoing effort by the CNRS team is to measure experimentally the spectral functions, in order to obtain a truly direct measurement of the mobility edge.
G. Semeghini, M. Landini, P. Castilho, S. Roy, G. Spagnolli, A. Trenkwalder, M. Fattori, M.Inguscio and G. Modugno, Measurement of the mobility edge for 3D Anderson localization, Nature Physics 11, 554–559 (2015).
See also the LENS group web page.