BaRbIE Project

An ion in a sea of ultracold neutral atoms


Control of Quantum Correlations in Tailored Matter
SFB/TRR 21 - Stuttgart, Ulm, Tübingen
The project is financially support by the Deutsche Forschungsgemeinschaft


We study the fundamental interactions of a single, trapped, laser-cooled Ba+ ion with ultracold 87Rb atoms. This experimentally unexplored terrain offers a multitude of fascinating experiments on the quantum level.

Here is a list of topics we would like to investigate in the near future:

  • Inelastic and elastic cold collisions between atoms and ions
    (Charge transfer, long range 1/r4 potential, huge scattering lengths)
  • Ultracold chemistry with neutral atoms and ions
    (charged, ultracold molecules)
  • Demonstrate the formation of a predicted mesoscopic molecular bound state
    (see R. Cote et al., PRL 89,  093001 (2002) )
  • Study polaronic physics of charged impurities in the BEC
    (dressing of ions, screening and tuning of interaction, effective mass, polaron binding energy)
  • Controlled entanglement of single atoms and ions
    (using a Mott insulator state of atoms in an optical lattice)

The Experimental Setup

Overview of the vacuum system: The MOT chamber, the BEC chamber and the science chamber (red) are connected via two differential pumping stages (purple). Each chamber is evacuated by its own pumping section (green) and can be separated from the rest by closing one of the gate valves.

We have completed setting up the experimental apparatus. It features a MOT chamber for initial laser cooling of the 87Rb atoms which are then magnetically transferred into a BEC chamber. Here, the Rb BEC is produced via forced evaporative cooling. With an optical standing wave the condensate is then transported into an ion trap chamber where a single Ba+ ion is located in a linear Paul trap.

Combined atom-ion trap: A linear radiofrequency Paul trap is used to store ions, whereas the ultracold atoms are confined in a crossed optical dipole trap. By precisely overlapping the positions of these two traps, a single ion can be immersed into the center of the ultracold neutral atom cloud.

The ion trap chamber features a linear Paul trap specifically designed to allow for the insertion of a standing wave dipole trap transporting an ultracold cloud of neutral atoms to the position of the ion. An objective lens system is installed inside the vacuum chamber facilitating efficient simultaneous flourescence imaging of the ion and absorption imaging of the atomic cloud.

Number of Rb atoms remaining in the trap depending on the position of the Rb+ ion relative to the center of the atom cloud. The measurement is performed with (a) a thermal cloud, (b) a partially condensed cloud and (c) an almost pure Bose-Einstein condensate.


Current Status

False color picture of the Rb gas undergoing Bose-Einstein condensation --- Three lasercoold Ba ions in the linear Paul trap

At the beginning of 2010, we have for the first time observed cold atom-ion collisions (arXiv:1007.4717). On February 22nd, we have moved our apparatus from Innsbruck to Ulm. Recently, we have trapped strings of 138Ba ions for the first time here in Ulm. Also, we are again able to produce 87Rb Bose-Einstein condensates in our science chamber consisting of up to 105 atoms.