It has been shown that the system of an impurity in a Bose-Einstein condensate can be described by the Frölich Hamiltonian. This generic model has many applications in different branches of physics. One of these is the well known polaron in solid state physics which consists of an electron coupled to the phonons of the crystal. Despite the many applications there are still some important outstanding issues about the strong coupling regime of the model. The main reason these haven't been solved yet is that the strong coupling regime doesn't appear in solids.
We look at this particular model in an ultra cold gas because in these it is possible to very accurately tune some of the aspects of the experiment, as for example the interaction strength between particles. This will allow us to make measurements in the regime of strong coupling for the first time.
The purpose of the project is to develop the theoretical description for this system. We will calculate the response properties for arbitrary coupling and also the effect of multiple impurities. Doing the predictions we will always keep the experiment in mind which will allow us to probe the strong coupling properties of the model.