Chemical exchange processes in an ultracold sample of cesium atoms directly observed
A research group led by Rudolf Grimm of the Institute for Experimental Physics of the University of Innsbruck and the Institute for Quantum Optics and Quantum Information (IQOQI) of the Austrian Academy of Sciences, have for the first time been successful in directly observing chemical exchange processes in an ultracold sample of cesium atoms and Feshbach molecules. (For more information on ultracold gases please refer to the following post: Study of ultra-cold degenerate Bosons and ultra-cold degenerate Fermions – Part 8). Rudolf Grimm and his team of physicists have now succeeded in directly observing and also energetically controlling an exchange process in a quantum gas. Grimm says, “Our experiment showed that it is possible to control exchange processes involving ultracold molecules”.
The scientists optically trap cesium atoms and cool them dramatically. A Feshbach association results in an ultracold particle cloud consisting of about 4,000 molecules and 30,000 atoms, where a part of the atoms are arranged in dimers. By applying a microwave pulse, the atoms are transferred into another quantum state without the molecules being modified. After preparing this mixture of molecules (A+A) and atoms (B), the physicists apply a certain magnetic field, which allows them to fully control the binding energy of the molecules. The collision of the molecules and atoms results in an exchange process when a certain threshold of binding energy is reached. The original molecules decay to atoms (A) and new molecules are produced (A+B). Grimm explains, “Since the energy produced in this exoergic process is very low, the reaction products remain in the trap. Thus, we were able to directly observe the chemical process for the first time ever.”
When a molecule (two blue spheres) collides with an atom (single red sphere), an atom can be exchanged. A new molecule is produced (red and blue spheres) and an atom (single blue sphere) is released. In the experiment performed in Innsbruck this process is observed at temperatures of less than one millionth above the absolute zero. The exchange is completely determined by the quantum nature of the matter and can be controlled by a magnetic field.
Image Source: Institute for Quantum Optics and Quantum Information (IQOQI) http://iqoqi.at/download
February 2, 2010