The aim of this project is to create an exotic dual species condensate comprising groundstate Rb atoms and excited state He* atoms. If successful, the mixture could then be used to create truly unique Rb-He* dimers.

In particular we aim to:

• demonstrate a new type of cooling: optical sympathetic cooling. Such a cooling method, that relies on the interactions between Rb and He* atoms, could significantly increase the number of condensate atoms produced per unit time.
• create the first Bose-Einstein condensate mixture comprising a metastable atom and a ground state atom.

The idea of sympathetically cooling He* through elastic collisions with Rb atoms is an intriguing one. At present the only successful path to creating Bose-Einstein condensates (BEC) is through evaporative cooling. This method, while elegant, is extremely inefficient, since atoms need to be removed from the sample that is cooled. However, use of an optically cooled cloud of Rb atoms to act as a refrigerant for the metastable helium atoms has the potential to produce much larger condensates than are possible with present means. Standard optical polarization gradient cooling (PGC) [9] can reduce the temperature of a cloud of Rb atoms to less than 10μK which is not far above the BEC transition temperature for He*. There are still a number of open questions about such a scheme, which this project will answer.

Creating a dual Rb-He* Bose-Einstein condensate is also within the scope of this project. Such a mixed condensate system has never been achieved. Once again, because the interatomic potentials are unknown, parameters key to BEC formation are not determined, for example the Rb-He* cross species scattering length. Nonetheless, in the early stages these parameters can be measured via monitoring the rethermalisation rates of He* when the Rb temperature is changed.