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Quantum Optics

Ultracold atoms juggle spins with exceptional symmetry

München, 09/03/2014

LMU/MPQ scientists succeed in revealing a highly symmetric exchange of spins between ytterbium atoms in different electronic orbital states.

The different spin states of ytterbium atoms can be separated and then imaged (Graphics: LMU / MPQ, Quantum Many-Body Systems Division)

The physical behaviour of materials is strongly governed by the many electrons which can interact and move inside any solid. While an individual electron is a very simple object, carrying only mass, electric charge, and an internal rotation known as “spin”, the collective behaviour of many interacting electrons can be very complex, and understanding it is the key to understanding the properties of the material. The more complex materials, especially those for which the interactions involve the spin of the electrons, pose formidable theoretical challenges. This has prompted researchers in recent years to model such systems, using artificial crystals of light filled with gases of ultracold atoms, in order to mimic the electrons and investigate the collective behaviour in an exceptionally clean environment.

Researchers at the Ludwig-Maximilians-University in Munich and at the Max Planck Institute of Quantum Optics led by Dr. Simon Fölling and Professor Immanuel Bloch, Professor of Experimental Physics at LMU Munich and director at the Max Planck Institute of Quantum Optics, have now succeeded in showing that certain atoms can interact by exchanging their spin even between two different “electron orbital” states, and that they do so in a highly unusual, maximally symmetric fashion (Nature Physics, Advance Online Publication, 31 August 2014). For this, the scientists allowed atoms in several possible combinations of spin orientations to interact in a pair-wise fashion, and then analyzed the result of the interaction and the amount of energy associated with it. The existence of such spin-exchanging interactions and of a high spin symmetry in ytterbium was so far only predicted theoretically, and their experimental characterization paves the way for the experimental study of previously inaccessible quantum phenomena in electronic materials.