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Scientists Measure Magnetic Interaction Between Two Bound Electrons
An anonymous reader writes In a paper published in Nature (abstract), scientists report successfully measuring the magnetic interaction of two bound electrons of two different strontium (Sr) ions. The two ions were suspended in a quadrupole ion trap (a.k.a. a Paul trap), and the effects of ambient magnetic noise were mitigated by 'restricting the spin evolution [of the electrons] to a decoherence-free subspace that is immune to collective magnetic field noise.' The scientists measured the magnetic interaction of the two electrons as a function of distance and found that the force acting between the two was inversely dependant on the cubed distance between the electrons, consistent with Newton's inverse-cube law.
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From ingress "the force acting between the two was inversely dependant on the cubed distance between the electrons" This should not be understood as inverse cube force between the electrons. From article: "By varying the separation between the two ions, they were able to measure the strength of the magnetic interaction as a function of distance – confirming the expected inverse-cubic (1/d3) dependence of the interaction."
It is the strength of the interaction that is found to be inverse cubic. The strength of magnetic force is inverse quadratic. If somebody found evidence of an inverse cubic force then this would be evidence of higher-spatial dimensions and very unexpected indeed. There has been speculation that gravity might be higher-dimensional at very small scales, but I have never heard anyone make this claim of of electromagnetic forces. The cross-product nature of the electric/magnetic interaction makes these forces a true child of an 3 dimensional space.
Neat! Newtonian physics at the atomic level. Does anyone know if the inverse square law has been tested in other ways at this scale? Or other Newtonian laws?
The phenomenon was known, a hypothesis existed to predict the results, and a test was devised to confirm the hypothesis. One critique, the article only mentions one Strontium ion separation, 10um. I would suggest that the test be repeated at multiple separations, and then determine if the data correlates with the predictions.
The big leap hear was observing the interaction of *only* 2 spins, not the physics. Just to be clear, this study has confirmed that standard spin physics work on the atomic scale. Confirming these basic laws for a system of two atoms is important because it can expose holes in our understanding of physics that came from only observing an ensemble of spins and not single spin states. Just a few notes: Derivations of quantum mechanical interactions come from basic formulas of classical mechanics, but strictly speak the physics in this paper are *NOT* Newtonian. They are talking about the energy of the interaction, not the force. For two electron dipoles interacting in space, the basic formulation come from F = (q1*q2)/(d^4). Because energy is force x distance: E = F*d = (q1*q2)/d^-3. This observation *is* expected since these physics govern basic magnetic resonance principles. The leap here comes from the fact that magnetic resonance experiments deal with LOTS of atoms, not two.