5th Institute of Physics

Cold Molecules

Laser cooling of molecules for applications in many-body physics, cold chemistry and tests of fundamental symmetries

The project

Laser cooling is a very well established technique for atoms, which is used extensively at our Institute and other labs around the world. It relies on the fact that atoms can repeatedly absorb and emit a large number of photons with the same wavelength. Even if the momentum of a single photon is very small, the scattering of many photons enables substantial slowing, and hence cooling, of the atoms.

Intuitively, it seems very challenging to apply this technique to molecules because of their complex level structure, which e.g. includes many rotational and vibrational levels. As a consequence, already after a few cycles of absorption and emission there is a very high probability for the molecules to fall into a state where they cannot scatter any more photons. We address this challenge by “engineering” suitable transitions in molecules that can scatter enough photons. For example, we carefully choose molecules, where all relevant vibrational states can be addressed with a small number of wavelengths. For rotational states we use selection rules and radio-frequency dressing to prevent decay of the molecules into unwanted levels. With these tools at hand, molecules can be brought all the way to microkelvin temperatures - despite being much more complex than atoms!

In fact, it is exactly this increase in complexity that makes cold molecules extremely interesting tools to study quantum mechanics. For example, many molecules feature strong and tunable dipole moments, which can be used to realize new forms of quantum matter (see here for our other work on dipolar gases).  Cold molecular collisions can give new insights into the foundations of chemistry. Finally, certain molecular level configurations can be used to search for new physics beyond the Standard Model of particle physics, using only a small tabletop experiment instead of a full-scale particle accelerator. 

Project Publications

  1. 2020

    1. D. Reens, H. Wu, A. Aeppli, A. McAuliffe, P. Wcisło, T. Langen, J. Ye, Beyond the limits of conventional Stark deceleration, Phys. Rev. Research 2, 033095 (2020).
    2. R. Albrecht, M. Scharwaechter, T. Sixt, L. Hofer, T. Langen, Buffer-gas cooling, high-resolution spectroscopy, and optical cycling of barium monofluoride molecules, Phys. Rev. A 101, 013413 (2020).
  2. 2018

    1. T. Langen, M. J. Mark, Ultrakalt magnetisiert, Physik Journal 17, 35 (2018).
    2. H. Wu, D. Reens, T. Langen, Y. Shagam, D. Fontecha, J. Ye, Enhancing radical molecular beams by skimmer cooling, Phys. Chem. Chem. Phys. 20, 11615–11621 (2018).
    3. T. Langen, T. Schweigler, E. Demler, J. Schmiedmayer, Double light-cone dynamics establish thermal states in integrable 1D Bose gases, New J. Phys. 20, 023034 (2018).
  3. 2017

    1. T. Schweigler, V. Kasper, S. Erne, I. Mazets, B. Rauer, F. Cataldini, T. Gasenzer, T. Langen, J. Schmiedmayer, J. Berges, Experimental characterization of a quantum many-body system via higher-order correlations, Nature 545, 323–326 (2017).
    2. D. Reens, H. Wu, T. Langen, J. Ye, Controlling spin flips of molecules in an electromagnetic trap, Phys. Rev. A 96, 063420 (2017).

We are always looking for motivated new team members!

Student assistant (Hiwi) position during semester break:

The 5th institute of Physics (Prof. Pfau) is looking for students who would like to experience everyday work in a modern quantum optics laboratory during semester break.

A variety of techniques and skills will be used:

  • CAD Modelling / 3D printing
  • electronics
  • usage of optic devices/laser
  • measuring techniques

Previous experience with these techniques is an advantage but not a requirement.

Salary: normal Hiwi salary per hour, hours per week and schedule upon individual arangement.

Interested candidates should contact Tim Langen.
Are you interested in realizing a new cutting-edge experiment at the forefront of quantum physics?
PhD position in
Laser Cooling of Dipolar Molecules
at the 5th Institute of Physics, University of Stuttgart
The goal of this thesis will be the construction of an experiment to directly laser cool and study diatomic molecules. It has recently been shown that such molecules can be cooled by methods similar to those used in atomic physics [see e.g. Barry et al., Nature 512, 286 (2014)].
With applications ranging from quantum many-body physics to cold collisions and precision measurements, the creation of a cold molecular gas will enable many fascinating insights at the interplay of physics and chemistry.
Students will be able to learn about and apply a wide range of experimental techniques ranging from optics, lasers and electronics to programming and cryogenics.
If you are interested in learning more, please contact Tim Langen.

Please contact Tim Langen.

Project Team


This picture showsTim Langen

Tim Langen

Group Leader

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