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Sympathetic cooling of molecules with cotrapped atoms is an approach toward further cooling of molecules even to the temperatures of quantum degeneracy level. Theoretical calculation predicts that NH and N have favorable properties for sympathetic cooling.

N/NH Co-trapping : 1st Generation

Elastic to Inelastic ratio of N/NH

We cooled nitrogen atoms and NH molecules to 500mK using helium vapor. The species fell into a 4T deep magnetic trap created by two superconducting coils in an anti-Helmholtz configuration. We studied the collisions of the atoms and molecules with helium to elucidate spin relaxation mechanisms. Our results show that the N/NH inelastic collision rate is small enough to cool the NH molecules with N atoms using sympathetic cooling.

Sympathetic Cooling of N/NH

For the sympathetic cooling, the background density of helium should be low enough to thermally isolate atoms and molecules from their environment. In the 1st generation experiments, the helium buffer gas density was set by desorption of helium from a film coating the inside of the trapping cell. In this experiment, we use dilution refrigerator to ensure low enough helium vapor density. N atoms and NH molecules are produced by ablating nitride targets in the hydrogen molecule environment. After creation, they fall into the magnetic trap and we can study the collision behavior of N/NH at low temperature. As we lower the depth of the trap, we can cool the N/NH mixture further to increase the phase space densities of them.


  • Yat Shan Au
  • Eunmi Chae
  • Colin Connolly
  • Hsin-I Lu (Now working on CaH trapping)

Recent graduates:

  • Wes Campbell (Now as postdoc at Maryland)
  • Matt Hummon (Now a postdoc at Boulder)
  • Edem Tsikata (Now a postdoc at JPL)



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