Currently we are working on two different projects:
1. From macroscopic to mesoscopic clouds
The first project is aimed at creating an ultracold gas of fermionic atoms with a finite and controlled number of atoms.
A major motivation for this project is that both atoms and nuclei are actually formed from a defined number of fermionic constitutents, and the precice number of those constitutents shapes their specific properties. Many of those, such as the shells are a direct consequence of the fermionic nature of nucleons or electrons.
Thus, very similar properties are expected for such systems composed of atoms. However, such an atomic system will immediately provide the experimenter with a number of extra benefits. There will be an incredible freedom of tuning both the confinement of the atoms in a trap as well as the interactions of the atoms with each other independently. Also, almost arbitrary compositions of atoms in different internal spin states should be possible, including such sytems that are known as halo nuclei in nuclear physics. This flexibility will open up a completely new range of exotic mesoscopic systems that could be studied.
Here is how we plan to make these dreams come true:
step 1: Create a Bose-Einstein condensate of molecules
Since the first creation of molecular condensates composed of fermionic atoms in the fall of 2003, several groups have been able to reproduce these results, and those condensates have proven to be a wonderful starting point for experiments with ultracold interacting Fermions.
For our experiments, this will be a robust starting point to have a very low temperature fermionic gas.
Here you can see how we produce our molecular BEC.
step 2: Transfer the condensate into a microtrap
For our finite atom number systems, most interesting effects such as the
shell structure will only become apparent, if the temperature is much lower than
any vibrational excitations:
kB T =
Such temperatures can only be achieved in present experiments,
if the vibration frequencies are extremely high such as in a lattice, or in a
microtrap. As we would like to go for a trap that contains tens of atoms, a microtrap is the way to go.
step 3: Spill most atoms from the microtrap in a controlled way
Provided we are able to achieve low enough temperatures, how will we be able to trap a defined number of atoms? We will again make use of an important property of a microtrap: Given a certain trap depth, the number of quantum states for the trapped atoms is relatively low. In fact it can be made so low that only very few quantum states will be left in the trap. Then, any additional atoms will immediately be lost from the trap. Of course it will be essential that we are able to control the trap potential well enough to be sure that we can actually tune the number of quantum states. But we are confident that in our microtrap we can actually do that!
2. Three-component Fermi gases
We are able to prepare a balanced three-component Fermi gas with about 50 000 atoms in each state. The sample consisting of 6Li atoms in the three lowset hyperfine states has a temperature of 215 nK, which corresponds to T/TF = 0.37. This new system offers the possibility to explore new many body phenomena like for example pairing competition or trimer formation. For more information and recent results click here or look on the arXiv:0806.0587.