Ultracold Polar Molecules

Ultracold Polar Molecules

Engineering and probing long range interacting molecular quantum gases.

In this experiment we aim to create a strongly interacting gas with long range interactions. Polar ground state molecules in an external fields provide tuneable dipolar interaction.

Polar molecules - A Quantum Gas with Long-range Interactions

Extending rotational coherence of NaK molecules

Diatomic molecules are currently the most complex objects that can be theoretically understood in full, quantum-mechanical detail. This makes them fascinating objects of study, because they show a wide range of complex and interesting behaviours, many of which are just now coming into our reach of understanding. We are mostly interested in two aspects of the physics of dipolar molecules: On the one hand, we want to understand the molecules themselves. This includes their internal structure and how it determines their chemistry and behaviour in molecule-to-molecule collisions. On the other hand, this knowledge can be used to control the internal quantum states of molecules and use them as building blocks for quantum simulators. Here, they can be used to realize systems that are not reachable with atoms. For example, long-range interactions in ultracold quantum gases of dipolar molecules offer new and fascinating possibilities for investigating quantum matter. While in many quantum gases, the many-body physics is dominated by contact interaction, dipole-dipole interactions offer a path to systems governed by long-range interactions.

Dual-Species Quantum Gas

Since direct cooling of molecules to quantum degeneracy is not yet possible, we first produce a mixture of sodium and potassium atoms in two-species magneto optical trap. To achieve ultracold temperatures in both atomic species, we perform evaporative cooling first in a magnetic and then in an optical dipole trap. We can achieve Bose-Einstein condensation of Sodium with up to 105 atoms. The same number of fermionic Potassium atoms are sympathetically cooled by the sodium cloud to near quantum degeneracy. For making molecules however, we stop cooling slightly above the temperature required for quantum degeneracy

Molecules in the Ground State

Stimulated Raman Adiabatic Passage

We apply a radiofrequency pulse to the mixture, causing association of molecules in a weakly bound metastable state. These are transferred to the electronic, vibrational and rotational ground state via stimulated Raman adiabatic passage, using a pair of lasers at 487 nm and 652 nm. To ensure mutual coherence of these lasers during the transfer time, both are stabilized to relative linewidths of 10-12 or lower. Only afterwards are the molecules long-lived and can be polarized.

Current Research

Currently, we are working improving our molecule numbers to hopefully reach degeneracy soon. For this, we are investigating grey molasses cooling of sodium and improved methods of associating Feshbach molecules, both in bulk and in a 3D optical lattice.

This is only the beginning of polar molecule research. If you would like to join this endeavor, let us know! We are always looking for talented new team members.

Selected Recent Publications

Seeßelberg, F.; Luo, X.; Li, M.; Bause, R.; Kotochigova, S.; Bloch, I.; Gohle, C.: Extending Rotational Coherence of Interacting Polar Molecules in a Spin-Decoupled Magic Trap. Physical Review Letters 121 (25), 253401 (2018)
Seeßelberg, F.; Buchheim, N.; Lu, Z.-K.; Schneider, T.; Luo, X.; Tiemann, E.; Bloch, I.; Gohle, C.: Modeling the adiabatic creation of ultracold polar 23Na40K molecules. Physical Review A 97 (1), 013405 (2018)

Research Group Members

Bause, Roman
Doctoral candidate
  • +49 89 3 29 05 - 284 (Office) // -273 (Lab) //
  • -279 (Prep lab)
Chen, Xingyan
Doctoral candidate
  • +49 89 32905 293 (Office) // -273 (Lab) //
  • -279 (Prep lab)
Duda, Marcel
Doctoral candidate
  • +49 89 3 29 05 - 629 (Office) // -273 (Lab) //
  • -279 (Prep lab)
Luo, Xinyu Dr.
Group Leader
  • +49 89 3 29 05 - 283 (Office) // -273 (Lab) //
  • -279 (Prep lab)
Schindewolf, Andreas Dr.
  • +49 89 3 29 05 - 293 (Office) // 273 (Lab) //
  • -279 (Prep lab)
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