Open quantum systems, and phase transitions in driven dissipative systems.  Light matter interactions.  Non-equilibrium phase transitions.  Cold atoms in optical cavities.  Strong coupling between matter and light.

PhD, University of Cambridge, 2005

B.A./M.Sci, University of Cambridge, 2002

My research focuses on coupled matter-light systems, and on non-equilibrium phase transitions in those systems.  Strong coupling between matter and light can be achieved by placing matter in optical cavities, concentrating the electromagnetic field strength and thus the coupling to matter.  Examples of this include microcavity polaritons, where photons in a microcavity couple to electronic excitations of solid state systems.  This can involve both excitons (bound electron hole pairs) in standard semiconductors, as well as electronic excitations in organic materials.  Other examples involve ultracold atoms in optical cavities, or superconducting circuits in microwave resonators.

In all these systems, it is possible to couple together large numbers of interacting systems, and thus to potentially see collective behaviour, such as phase transitions.  However, no real physical system can perfectly contain light, and so this collective behaviour is of a new class, phase transitions in open quantum systems, where loss has to be balanced by some form of external pumping.

My current research interest has three main strands:

• Cold atoms in optical cavities.  Here we focus on how ongoing experiments by the Lev group in Stanford can be used to explore the physics of phase transitions in open quantum systems, and to provide new tools for quantum simulation.
• Exact numerical methods for phase transitions in open systems: Here we develop approaches based on matrix product states to give a generic understanding of the physics of phase transitions in open systems, focussing on solvable models.
• Strong matter light coupling with complex materials.  In particular, we focus extensively on the physics of organic molecules.  Here it is possible to use matter light coupling to change the conformation of molecules, and potentially alter chemical reaction rates.  We are also particularly interested in the interplay of this coupling with electronic transport in these materials.

Group website

I currently teach part of the final-year "Quantum Field Theory" course (also open to graduate students).  I also teach a biennial graduate course on quantum phase transitions and quantum magnetism. 

Theoretical condensed matter. Open quantum systems.  Strong matter-light coupling. Microcavity polaritons.