"Bose-Einstein Condensation of Light" Prof. Martin Weitz

Abstract

Bose-Einstein condensation, the macroscopic ground state occupation of a system of particles with integer spin (bosons) below a critical temperature, has been observed in cold atomic gases and solid-state physics quasiparticles. In contrast, photons do not show this phase transition usually, because in Planck’s blackbody radiation the particle number is not conserved and at low temperature the photons disappear in the walls of the system. I will describe an experiment realizing a photon Bose-Einstein condensate in a dye-filled optical microcavity, which acts as a “white-wall” photon box. The cavity mirrors provide a trapping potential and a non-vanishing effective photon mass, making the system formally equivalent to a two-dimensional gas of trapped massive bosons. Thermalization of the photon gas is reached in a number conserving way by repeated absorption re-emission cycles in the dye molecules. More recently, we have investigated the transition between usual lasing and photon Bose-Einstein condensation and also measured the coherence of the photon gas. In my talk, I will begin with a general introduction and give an account of current work of the Bonn photon gas experiment and future plans.

Biography

Martin Weitz is a Professor of Experimental Physics at the University of Bonn in Germany. He studied physics and electrical engineering at the University of Kaiserslautern and the Technical University of Munich. He received his PhD in natural sciences from the University of Munich for work on precision spectroscopy of atomic hydrogen under supervision of Prof. T. W. Hänsch. After a postdoctoral stay at Stanford University and joining the Max Planck Institute of Quantum Optics in Garching he became Professor at the University of Tübingen in 2001. Since 2006 he is full professor at the University of Bonn. In 2012 he received an Advanced Grant of the European Research Council for research on Bose-Einstein condensation of photons in optical microcavities. His current research interests include collective photonic effects, the quantum physics of ultracold atomic gases in optical lattices, and novel laser cooling techniques.