University of St Andrews

In specially engineered light-matter structures photons can be made to interact strongly, which leads to a wide range of collective behaviours from order-disorder phase transitions and superfluidity to topological phases. However, normally their intrinsically dissipative nature results in highly non-equilibrium conditions leading to new phenomena which only start being explored. At the same time state-of-the-art semiconductor microcavities allowed recently to achieve a fully thermalised photonic system analogous to cold atoms or liquid Helium. I will discuss a few examples of non-equilibrium collective effects in such systems, as well as the recently achieved equilibrium limit. 

Active materials, such as bacteria, molecular motors and self-propelled colloids, are Nature’s engines. They continuously transform chemical energy from their environment to mechanical work. Dense active matter shows mesoscale turbulence, the emergence of chaotic flow structures characterised by high vorticity and self-propelled topological defects.  The ideas of active matter are suggesting new ways of interpreting cell motility and cell division. In particular recent results indicate that active topological defects may help to regulate turnover in epithelial cell layers and contribute to controlling the structure of bacterial colonies.