# Berlin 2014 – wissenschaftliches Programm

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# Q: Fachverband Quantenoptik und Photonik

## Q 32: Poster: Quantum gases, ultracold atoms and molecules

### Q 32.29: Poster

### Mittwoch, 19. März 2014, 16:30–18:30, Spree-Palais

**Cavity QED in the Recoil Resolved Regime** — •Hans Keßler, Jens Klinder, Matthias Wolke, and Andreas Hemmerich — Institut für Laserphysik, Universität Hamburg

We are experimentally exploring the light matter interaction of a Bose-Einstein condensate (BEC) with the light mode of an ultrahigh finesse optical cavity (*F*≈ 340 000).
The key feature of our cavity is the small intracavity field decay rate (κ/2π≈ 4.5 kHz), which is half the spectral width of the transmission resonances.
Most importantly, this decay rate is smaller than twice the recoil frequency (ω_{rec}/2π≈ 3.55 kHz) or rather the spectral linewidth is smaller than the frequency change of a photon in a single backscattering event.
Together with a Purcell factor of η≈ 40 ≫ 1, this leads to a unique situation where each atom can backscatter only a single photon, because the kinetic energy transfer required for further backscattering is not resonantly supported by the cavity.
With our setup we were able to demonstrate targeted heating and cooling of atoms on a sub-recoil energy scale at densities on the order of 10^{14} cm^{-3} incompatible with conventional laser cooling which relies on the scattering of near resonant photons [1].

Furthermore, the inaccessibility of higher momentum states leaves us with a true two level system interacting with our narrowband cavity. This model system gives us the opportunity to investigate novel aspects of light matter interaction like exotic quantum phase transitions or attractors in cavity optomechanics.

[1] M. Wolke, J. Klinner, H. Keßler, and A. Hemmerich, Science 337, 75 (2012)