Dipolar Quantum Gas of NaK Molecules

Dipolar Quantum Gas of NaK Molecules

Strongly-interacting dipolar quantum gas of 23Na40K ground-state molecules

We study ultracold polar molecules, not because it is easy, but because it is hard. 
adapted from JFK

In our Lab, we are able to create dipolar quantum gases of NaK molecules by assembling ultracold mixture of sodium and potassium atoms. Their strong and anisotropic long-ranged intraction allows us to investigate the rich physics of dipolar many-body system in a strongly-interacting regime. We are particularly interested in the following three directions.


1. Strongly-interacting Bose-Fermi mixture 
Understanding the many-body physics of a Bose-Fermi mixture is crucial to make quantum gas of 23Na40K polar molecules.  Such mixtures with different quantum statistics are fascinating in their own right because of its rich phase diagram with distinguishing features compared to pure fermionic or bosonic systems.  However, Bose-Fermi mixtures in the strongly-interacting regime remained largely unexpored in experiments due to severe collisional losses . Recently we have developed a species-dependent dipole trap technique which allows us to investigate the quantum phase transition of a density-matched Bose-Fermi mixture and produce a degenerate Fermi gas of NaK molecules.

2. Ultracold collisions of atoms and molecules
We want to understand various collisional processes of molecules and atoms which are crucial to cool and stabilize molecules. We use external electric fields to tailor the long-range part of the molecules interaction in order to make strongly-interacting stable molecular quantum gas.  Recently we have loaded NaK molecules into a dark box trap in order to investigate the photon-induced loss of non-reactive bialkali molecules. Surprisingly we found a descrepancy at least two orders of magnitude with the latest collision model. more
3. Spin models beyond nearest-neighbor interactions
We trap molecules in optical lattices to simulate novel spin models and extended Hubbard model beyond nearest-neighbor interactions. In our previous works, we have extended the rotational coherence time of polar molecules to 10 ms by using a spin-decoupled magic trap. Therefore we observe a density-dependent decoherence which is an evidence of dipolar interaction of molecules in a bulk gas. more


Starting from hot vapors of sodium and potassium at 330 and 50 degrees Celsius respectively in ultra-high vacuum chambers, we first produce a mixture of sodium and potassium atoms at about 100 μK in two-species magneto optical traps. To achieve quantum degeneracy, we perform evaporative cooling first in a pluged magnetic trap and then in an optical dipole trap. We can prepare a density-matched mixture of Bose-Einstein condensate of 0.8 × 105 sodium and deeply-degenerate Fermi gas of 2 × 105 potassium at about 100 nK in a species-dependent dipole trap. The Bose-Fermi mixture is then associated to 50000 long-lived weakly-bound Feshbach molecules at 0.3 Fermi temperature by ramping the magnetic field through a Feshbach resonance and transferred to the rovibronic ground state via stimulated Raman adiabatic passage (STIRAP). This gives us a good starting point for studying novel spin models with strong dipolar interactions in optcial lattices.

Our Sodium laser system

Our Sodium laser system

A picture of our yellow sodium MOT.

A picture of our yellow sodium MOT.

And a picture of our Potassium MOT.

And a picture of our Potassium MOT.

Our vacuum system

Our vacuum system



June 2023  Our preprint of  ultracold field-linked tetratomic molecules on arxiv! 

October 2022  Our preprint of the long-predicted  field-linked resonances of polar molecules on arxiv! 

February 2022  Our preprint  long-lived NaK fermionic Feshbach molecules on arxiv! Together with the work  three-body loss in a degenerate Bose-Fermi mixture, we have systematically investigated the collisions in a 23Na-40K Bose-Fermi mixture.

January 2022  Our paper of  evaporative cooling of NaK molecules in 3D on arxiv!

November 2021 Our paper of degenerate NaK fermionic molecules on arxiv!

June 2021 Our paper of [new STIRAP technique] on arXiv. Here we show how filter cavities can improve the STIRAP efficiency! 

April 2021 Fermionic NaK polar molecules entered the quantum degenerate regime! Paper in preparation, stay tuned!

September 2020 First ultracold polar molecules in a box trap! 

March 2020 Our new all-solid-state STIRAP laser system ready!  Well done Akira!

We are always looking for motivated undergraduate, Master and PhD students. If you are interested of  joining us, please contact Prof. Bloch (immanuel.bloch(at)mpq.mpg.de) 

Selected Recent Publications

Xingyan Chen, Shrestha Biswas, Sebastian Eppelt, Andreas Schindewolf, Fulin Deng, Tao Shi, Su Yi, Timon A. Hilker, Immanuel Bloch, and Xinyu Luo, "Ultracold field-linked tetratomic molecules," Nature 626, 283 (2024).
Marcel Duda, Xingyan Chen, Andreas Schindewolf, Roman Bause, Jonas von Milczewski, Richard Schmidt, Immanuel Bloch, and Xinyu Luo, "Transition from a polaronic condensate to a degenerate Fermi gas of heteronuclear molecules," Nature Physics 2023 (2023).
Xingyan Chen, Andreas Schindewolf, Sebastian Eppelt, Roman Bause, Marcel Duda, Shrestha Biswas, Tijs Karman, Timon A. Hilker, Immanuel Bloch, and Xinyu Luo, "Field-linked resonances of polar molecules," Nature 614, 59-63 (2023).
Roman Bause, Arthur Christianen, Andreas Schindewolf, Immanuel Bloch, and Xinyu Luo, "Ultracold Sticky Collisions: Theoretical and Experimental Status," The Journal of Physical Chemistry A (2023).
Andreas Schindewolf, Roman Bause, Xingyan Chen, Marcel Duda, Tijs Karman, Immanuel Bloch, and Xinyu Luo, "Evaporation of microwave-shielded polar molecules to quantum degeneracy," Nature 607, 677-681 (2022).
Xingyan Chen, Marcel Duda, Andreas Schindewolf, Roman Bause, Immanuel Bloch, and Xinyu Luo, "Suppression of Unitary Three-body Loss in a Degenerate Bose-Fermi Mixture," Physical Review Letters 128 (15), 153401 (2022).
Bause, R.; Schindewolf, A.; Tao, R.; Duda, M.; Chen, X.; Quemener, G.; Karman, T.; Christianen, A.; Bloch, I.; Luo, X.: Collisions of ultracold molecules in bright and dark optical dipole traps. Physical Review Research 3 (3), 033013 (2021)
Bause, R.; Li, M.; Schindewolf, A.; Chen, X.-Y.; Duda, M.; Kotochigova, S.; Bloch, I.; Luo, X.: Tune-out and magic wavelengths for ground-state 23Na40K molecules. Physical Review Letters 125, 023201 (2020)
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

M. Sc. Shrestha Biswas
Doctoral candidate
  • +49 89 3 29 05 - 293 (Office) // - 273 (Lab)
Dr. Xing-yan Chen
  • +49 89 32905 293 (Office) // -273 (Lab)
Dr. Xinyu Luo
Group Leader
  • +49 89 3 29 05 - 283 (Office) // -273 (Lab) //
  • -279 (Prep lab)
Dr. Andreas Schindewolf
  • +49 89 3 29 05 - 293 (Office) // 273 (Lab) //
  • -279 (Prep lab)

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