Macroscopic phase coherence is one of the most remarkable manifestations of quantum mechanics, yet it seems to be the inevitable ground state of interacting many-body systems. In the last two decades, the familiar examples of superfluid He and conventional superconductors have been joined by exotic and high temperature superconductors, ultra-cold atomic gases, both bosonic and fermionic, and recently systems of excitons, magnons, and exciton-photon superpositions called polaritons, the subject of this talk.
Engineering of optical microcavities make use of the mixing of electronic excitations with photons to create a composite boson called a polariton that has a very light mass, and experiments provide good evidence for a high-temperature Bose condensate. Polariton systems also offer an opportunity to use optical pumping to study quantum dynamics of a many body system outside equilibrium, in a new kind of cold atom laboratory. We suggest that a new kind of dynamical phase transition is available in these two-component condensates, associated with the presence of a many-body exceptional point that has two degenerate real eigenvalues corresponding to coalescing solutions – a dynamical-systems equivalent to a critical point of a regular phase transition.
Peter B Littlewood is a Professor of Physics at the University of Chicago, who was previously Director of Argonne National Laboratory, and before that a Professor of Physics at the University of Cambridge and Head of the Cavendish Laboratory. He is the Founding Executive Chair of the Faraday Institution, UK’s independent centre for electrochemical energy storage science and technology, supporting research, training, and analysis. He began his career with almost 20 years at Bell Laboratories, ultimately serving for five years as head of Theoretical Physics Research.
His research interests include superconductivity and superfluids, strongly correlated electronic materials, collective dynamics of glasses, density waves in solids, neuroscience, and applications of materials for energy and sustainability. He is a fellow of the Royal Society of London, the Institute of Physics, the American Physical Society, and TWAS (The World Academy of Sciences). He serves on advisory boards of research and education institutions and other scientific organizations worldwide. He holds a Bachelor’s Degree in Natural Sciences (Physics) and a Doctorate in Physics, both from the University of Cambridge.