Strongly-interacting dipolar quantum gas of 23Na40K ground-state molecules
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.
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.
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.
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.
Roman Bause, Andreas Schindewolf, Renhao Tao, Marcel Duda, Xingyan Chen, Goulven Quemener, Tijs Karman, Arthur Christianen, Immanuel Bloch, and Xinyu Luo, "Collisions of ultracold molecules in bright and dark optical dipole traps," Physical Review Research 3 (3), 033013 (2021).