Experimental Observation of Many-Body Localisation using Ultracold Fermions in a Quasirandom Optical Lattice

Tuesday, 12 July, 2016 -
15:00 to 16:00

Localisation of non-interacting particles due to a disordered potential was first predicted by Anderson in 1958.  Recently, the effect of interactions on Anderson localisation (many-body localisation or MBL) has become the subject of much theoretical investigation.  MBL signals a breakdown of conventional thermodynamics, as such systems do not thermalise and exhibit nonergodic time evolution.

We experimentally observe this nonergodic behaviour using interacting ultracold fermions in a 1D quasirandom optical lattice.  Above a critical disorder strength a substantial fraction of the ordering in an initially prepared state persists at long times, indicating localisation and non-ergodic dynamics. The critical disorder strength shows a distinctive dependence on the interaction strength, characteristic of MBL.

Additionally, we investigate the effects of coupling such a system to different types of bath-like external structures, either by coupling adjacent 1D systems or via photon scattering.  We study how MBL breaks down due to such coupling and over what timescale this occurs.