Abstract

n this talk, I describe how cold atoms can be used to test two phenomena which play a key role in our description of quantum many-body physics.

The first is the Higgs mode, which plays a fundamental role for our understanding of both low and high energy physics, giving elementary particles their mass and leading to collective modes in condensed matter and nuclear systems. The Higgs mode has been observed in a limited number of table-top systems, where it however is characterised by a short lifetime due to decay into a continuum of modes. A major goal which has remained elusive so far, is therefore to realise a long-lived Higgs mode in a controllable system. Here, we show how an undamped Higgs mode can be observed unambiguously in a Fermi gas in a two-dimensional trap, close to a quantum phase transition between a normal and a superfluid phase. The second phenomena is the hexatic phase, which is a phase in between a liquid and a crystal. We show how such a phase can be realised in the quantum regime for the first time, using a two-dimensional gas of dipolar molecules. We derive approximate phase diagrams using a pair of Lindemann criteria, suitably adapted to deal with effects of thermal fluctuations in two dimensions. The hexatic phase is predicted to survive down to very low temperatures.