There have been many theory papers in the past ten years discussing the interactions between an ion, or multiple ions, and a Bose-Einstein condensate. However, little experimental work has been done in this regard. To perform an experiment involving an ion and a BEC, several things are necessary:
As can be seen in other parts of this webpage, we have already accomplished the first item on this list. All that remains, then, is to modify our system to accomodate ions.
We create our ions directly from the BEC with the two-photon transition 5S1/2 to 5P3/2 to continuum, which requires 780 nm and 480 nm light. By using a short, weak pulse of 480 nm light, we can control how many BEC atoms we photoionize.
We have chosen to control the ions passively rather than actively. They are untrapped, so we must be concerned with stray electric fields, which could force an ion out of the vicinity of a BEC before it has time to interact with the BEC. We use a set of electrodes to cancel all stray electric fields in all directions:
Near the ions, grown onto the center mirror used for the secondary MOT, we have a point-like electrode "tip," electrically isolated from the rest of the mirror:
When a positive potential is put on the tip, the ions follow the electric field lines going radially outward. Thus, their distribution is magnified as they travel farther from the tip. Eventually, they hit an MCP placed on the other end of the vacuum chamber; the MCP can spatially image them, or measure their arrival time with high accuracy. Along the way, the ions pass through a set of ion lenses consisting of three rings. These lenses can be used to increase or reduce the magnification.