# From Casimir-Polder force between an atom and a topological insulator to Dicke physics

## Sebastian Fuchs

### (Physikalisches Institut, Albert-Ludwigs University of Freiburg)

Time: Tue Feb 16 13:00:00 2016

Location: Building 1, Room 123

In the first part of the talk I am going to discuss how the theory of macroscopic quantum electrodynamics in dispersing and absorbing media is applied to study the Casimir-Polder force between an atom and a topological insulator [1]. The electromagnetic response of a topological insulator surface leads to a mixing of electric and magnetic fields, breaking the time-reversal symmetry [2, 3]. The coupling of these fields to an atom causes shifts of the atom’s eigenenergies and modified decay rates near the surface of the topological insulator.

In the second part we study superradiance that is associated with two physical effects: Firstly, the cooperative emission of radiation of a large number of excited atoms into free space in a quick, strong 'superradiant burst'. Secondly, fur sufficiently strong coupling of many atoms to an electromagnetic cavity mode, modeled with the Dicke Hamiltonian, a 'superradiant phase' is found, which shows macroscopic photon occupation and atomic excitation. The two facets of superradiance can be combined in studying the dissipative dynamics of an initially excited state of a mesoscopic number of atoms towards equilibrium [4].

Combining macroscopic QED and Dicke physics opens the door to the investigation of cooperative atom-surface interactions.

[1] S. Y. Buhmann, Dispersion Forces II, Springer-Verlag Berlin Heidelberg (2012).

[2] S. Y. Buhmann, D. T. Butcher, and S. Scheel, New Journal of Physics 14, 083034 (2012).

[3] J. A. Crosse, S. Fuchs, and S. Y. Buhmann, Physical Review A 92, 063831 (2015).

[4] S. Fuchs, J. Ankerhold, M. Blencowe, and B. Kubala, Journal of Physics B 49, 035501 (2016).