Localisation of non-interacting particles due to a random disordered potential is a well understood phenomenon, first predicted by Anderson in 1958. However, it was less clear as to whether interactions between particles would destroy this localisation. Termed many-body localisation, this would represent a breakdown of conventional thermodynamics, as such systems do not thermalise and exhibit non-ergodic time evolution.
We experimentally observe this non-ergodic behaviour for the first time using a degenerate gas of interacting ultracold fermions in a 1D quasi-random optical lattice. Above a critical disorder strength a substantial amount of the ordering in an initially prepared state persists, indicating localisation and non-ergodic dynamics. Additionally, we investigate the effects of coupling adjacent 1D systems, which can destroy the localisation.
In a separate set of experiments we have demonstrated ghost imaging using ultracold helium atoms. Ghost imaging is a technique from quantum optics where correlations between two spatially separate beams allow the image of an object to be reconstructed even though no spatial information of particles that interact with it is recorded. This is the first demonstration of ghost imaging with massive particles.
Dr Sean Hodgman was awarded his PhD in Physics in 2011 from the ANU in the group of A/Prof Andrew Truscott, working with ultracold metastable helium atoms. From 2012-2015 he worked as a postdoc in the group of Prof Immanuel Bloch, at the Max Planck Institute for Quantum Optics in Munich, using degenerate quantum gases in optical lattices as experimental quantum emulators for solid state systems. In 2015 he returned to RSPE on a DECRA fellowship.