# How photons change the properties of matter

**Speaker:**

Michael Ruggenthaler, Max Planck Institute for the Structure and Dynamics of Matter, Hamburg

**Time, place:**

Thursday, May 11, 2017, 11:00h, Bibliothek A.2.500, MPL, Staudtstr. 2, 91058 Erlangen

**Abstract:**

In this talk I will present a brief overview of how well-established concepts of quantum chemistry and material sciences have to be adapted when the quantum nature of light becomes important in correlated matter–photon problems [1], and possible ways to tackle such situations with first-principle methods [2,3]. For model systems in optical cavities, where the matter–photon interaction is considered from the weak- to the strong-coupling limit, I highlight fundamental changes in, e.g., Born–Oppenheimer surfaces and spectroscopic quantities. As possible approaches to the matter-photon problem I introduce the Cavity Born-Oppenheimer approximation [2] and a density-functional reformulation of quantum electrodynamics [3,4]. For the latter I show first results for real systems.

**References**

[1] J. Flick, M. Ruggenthaler, H. Appel, and A. Rubio, "Atoms and molecules in cavities, from weak to strong coupling in quantum-electrodynamics (QED) chemistry", Proceedings of the National Academy of Sciences 114 (12), 3026-3034 (2017).

[2] J. Flick, H. Appel, M. Ruggenthaler, and A. Rubio, "Cavity Born-Oppenheimer Approximation for Correlated Electron-Nuclear-Photon Systems", J. Chem. Theory Comput. 13 (4), pp 1616–1625 (2017).

[3] M. Ruggenthaler, J. Flick, C. Pellegrini, H. Appel, I.V. Tokatly, and A. Rubio, "Quantum-electrodynamical density-functional theory: Bridging quantum optics and electronic-structure theory" Physical Review A 90 (1), 012508 (2014).

[4] J. Flick, M. Ruggenthaler, H. Appel, and A. Rubio, "Kohn–Sham approach to quantum electrodynamical density-functional theory: Exact time-dependent effective potentials in real space", Proceedings of the National Academy of Sciences 112 (50), 15285-15290 (2015).