Exotic Phase Transitions in Open Quantum Systems

In this talk I will show how phase transitions in open quantum systems can be richer than their equilibrium counterparts. To do this I will give two examples. The first shows how ideas of parity-time (PT) symmetry breaking can be generalised to quantum mechanical systems. After introducing some simple examples I will show how this effect can compete with the presence of a non-linear Hamiltonian to produce a very rich phase diagram. The second example considers a paradigmatic model for light-matter interactions, the Dicke model, generalised to include 2-photon interactions. I will show how, for this model, the behaviour is drastically altered by the presence of different dissipation mechanisms, removing an instability in the Hamiltonian.

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