Martin Zeppenfeld
Phone: +49 89 3 29 05 - 726

Cold Polar Molecules

Cold Polar Molecules


Dense and cold samples of polar molecules offer exciting prospects for various fields. This includes the study of chemical reactions at low temperatures, applications in quantum-information processing and quantum simulations, as well as the investigation of processes beyond the standard model, which can, e.g., cause a violation of time-reversal symmetry. Moreover, polar molecules attract a lot of interest due to their long-range, anisotropic dipole-dipole interactions. These interactions give rise to new scattering phenomena and the formation of exotic phases of quantum matter.

The primary challenge in pursuing these applications is developing techniques to generate molecule ensembles with the required low temperatures and high densities while simultaneously gaining control over the internal molecular states. Here, our group has pioneered a number of innovative techniques. Velocity filtering and buffer-gas cooling generate high-density molecular beams with kinetic energies in the co-moving frame on the order of 1K×kB. A centrifuge decelerator continuously slows these beams from over 100m/s almost to standstill. A microstructured electric trap allows us to hold on to the resulting cold molecules for over a minute.

Since laser cooling, the workhorse technique for generating ultracold atoms, is inapplicable to most molecule species, we have developed an alternative, optoelectrical Sisyphus cooling, to cool trapped molecules to the ultracold temperature regime (T<1mK). Molecules in our electric trap continuously lose and regain kinetic energy by exchanging energy with the electric fields which constitute the trap. Radiofrequency transitions and optical pumping via a spontaneous vibration decay forces the molecules to follow a path which leads to an overall loss in energy. This has allowed us to cool molecules over many orders of magnitude, resulting in record large ensembles of almost a million molecules at temperatures below 1mK.

Based on our success in creating cold and ultracold ensembles of molecules, we are presently increasingly focused on applications. Making use of the high densities achieved allows us to explore cold and ultracold collisions and chemistry, including phenomena such as tunneling-induced reactions and collision resonances. Collision investigations also pave the way for achieving even lower temperatures via sympathetic or evaporative cooling. The low temperatures we have already achieved also allow us to perform molecular spectroscopy with unprecedented precision, and to look for tiny shifts which might indicate physics beyond the standard model. Finally, a new project aims at realizing a quantum interface between polar molecules and Rydberg atoms. Such an interface will bring quantum control of molecules to a new level, including internal state control and nondestructive detection.

Research Topics

Open Positions

If you are interested in joining the group, please consult the Open Positions page, and contact Dr. Martin Zeppenfeld or Prof. Gerhard Rempe.

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