Quantum state also shapes "normal" magnets

Neutron beam makes restriction visible

Comparison of the classical concept (left) and the entanglement observed with the neutron beam. © London Center for Nanotechnology
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The quantum world has its own rules. So there exists a state of mysterious interconnectedness between two particles, the so-called entanglement. An international research team has now shown that this state also shapes the magnetism on the particle level - contrary to previous ideas. Their findings have appeared in the journal Proceedings of the National Academy.

Atoms also have a kind of magnetism. He expresses himself in her so-called "spin", a property similar to a direction of rotation. According to conventional reading, all spins of these atoms in magnetic materials point in the same direction. In so-called antiferromagnets, the atoms spontaneously arrange themselves so that their spins are oriented in the opposite direction to the spin of the respectively adjacent atom. This lifts their effect and the material is neutral.

But a recent study by scientists at the London Center for Nanotechnology (LCN) exposes this image as incorrect. Because it ignores the specific uncertainties of the quantum state. Because this involves a state of superposition in which a spin can point up and down simultaneously. In addition, two atoms and their spins can be linked by a so-called entanglement. Then both - even in the indefinite state of superimposition - always point in the opposite direction.

They demonstrated this effect using copper atoms on an organometallic surface. They developed evidence of entanglement in which neutrons play a crucial role. The significance of this work lies in the fact that the researchers demonstrated that a relatively conventional tool of material research - neutron beams, which are generated in a particle accelerator - can be used to depict the mysterious state of entanglement.

"When we started this work, none of us expected such tremendous entanglement effects in the material we studied, " explains Professor Des McMorrow. "We just followed a hunch that this material could reveal something important and were smart enough to follow that idea." As a next step, scientists also want to test their method on high-temperature superconductors. These have some similarities with antiferromagnets and could also play a role in the development of future quantum computers. display

(University College London, 24.09.2007 - NPO)