Ice-cold particle cloud in the laser trap

For the first time exchange reaction in ultracold quantum gas directly observed

When a molecule (two blue spheres) collides with an atom (single red sphere), an atom can be exchanged. This creates a new molecule (red plus blue sphere) and releases an atom (single blue sphere). In the Innsbruck experiment, this process takes place at temperatures of less than one millionth of a degree above absolute zero. The exchange is entirely determined by the quantum nature of matter and can be precisely controlled by applying a magnetic field. © IQOQI
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Great advances in the control of ultracold quantum gases open a new path to the study of chemical reactions. An international research team has for the first time succeeded in directly observing a chemical exchange reaction in an ultracold gas of cesium atoms and molecules. The scientists report on it in the journal "Physical Review Letters".

When molecules form in chemical reactions or, conversely, when molecular bonds are dissolved, this is usually determined by complex processes that are largely beyond direct observation. Some of these processes require energy - endothermic reactions - others release energy (exothermic reactions).

Particles in a well-defined quantum state

The great advances in the research of ultra-cold atomic and molecular gases make it possible for the first time to realize elementary chemical reactions in a fully controlled manner, so that all involved particles are in a well-defined quantum state.

Innsbruck quantum physicists led by Rudolf Grimm, together with American researchers, have for the first time directly observed and energetically controlled a so-called exchange reaction in a quantum gas. "With our experiment, we were able to show that the controlled reaction of ultracold molecules is possible, " Grimm is pleased to share with his team.

Reaction observed directly

The scientists capture cesium atoms in a laser trap and cool them down. By exploiting a Feshbach resonance, some of the atoms form molecules in pairs, creating an ultracold particle cloud of around 4, 000 molecules and 30, 000 atoms. With a microwave pulse, the atoms are put into another quantum state, without changing the molecules. display

The physicists then apply a magnetic field to this mixture of molecules (A + A) and atoms (B), with which they can very precisely control the binding energy of the molecules. When the molecules and atoms collide with each other, a simple exchange reaction occurs at a certain binding energy. The original molecules break down into atoms (A) and new molecules (A + B) are formed.

"Because the energy that is released during this exothermic process is extremely low, the reaction products remain in our laser trap, " explains Grimm. "So we were able to observe the chemical reaction directly for the first time."

Specialists in quantum gases

The researchers from the Institute of Experimental Physics at the University of Innsbruck and the Institute of Quantum Optics and Quantum Information (IQOQI) have long been working on the research of ultracold quantum gases. In 2002, for example, they succeeded in producing a Bose-Einstein condensate of C sium atoms for the first time. The first Bose-Einstein condensate of molecules and a Fermi condensate followed.

Today, quantum physicists are able to produce even more complex molecules in ultracold quantum gases. There is a whole new field of research, explains the basic researcher Grimm, in which, with the help of ultracold quantum gases, we can study chemical reactions in their full diversity in a very controlled way

(Institute of Quantum Optics and Quantum Information (IQOQI), 03.02.2010 - DLO)