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Collisions between cold molecules in a superconducting magnetic trap


Collisions between cold molecules are essential for studying fundamental aspects of quantum chemistry, and may enable the formation of quantum degenerate molecular matter by evaporative cooling. However, collisions between trapped, naturally occurring molecules have not been directly observed so far owing to the low collision rates of dilute samples. Here we report the direct observation of collisions between cold trapped molecules, without the need for laser cooling. We magnetically capture molecular oxygen in an 800-millikelvin-deep superconducting trap and set bounds on the ratio between the elastic- and inelastic-scattering rates—the key parameter determining the feasibility of evaporative cooling. We further co-trap atoms and molecules and identify collisions between them, paving the way for studies of cold interspecies collisions in a magnetic trap.

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Fig. 1: Experimental setup.
Fig. 2: Column-integrated density signal through the trap centre for different trap depths.
Fig. 3: Trapping of lithium.
Fig. 4: Spatial probing of the trap.
Fig. 5: Effect of collisional properties on the spatial variation of the decay rate.

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Data availability

The data that support the findings of this study are available from the corresponding author upon reasonable request.


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We thank A. Kuprienko of the Weizmann Chemical Research Support and H. Sade of the Weizmann CNC Section for assistance in designing and manufacturing the experiment components. We acknowledge funding from the European Research Council and the Israel Science Foundation. Y.S. acknowledges support from the Azrieli Foundation.

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Correspondence to Edvardas Narevicius.

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Extended data figures and tables

Extended Data Fig. 1 Density decay for two limiting cases.

The blue curve represents the density distribution shortly after loading, with all particles with bound trajectories remaining. For the case of only inelastic collisions (γ = 0), the density distribution after 10% of the particles have been lost exhibits an almost uniform decay (green). By contrast, the corresponding distribution for only elastic collisions (γ → ∞) displays an increase in density near the trap centre. The trap radius is 4 mm.

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Segev, Y., Pitzer, M., Karpov, M. et al. Collisions between cold molecules in a superconducting magnetic trap. Nature 572, 189–193 (2019).

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