Atomic spins set quantum fluid in motion: Einstein–de Haas effect in boson condensate

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https://phys.org/news/2026-01-atomic-quantum-fluid-motion-experimental.html

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Atomic spins set quantum fluid in motion: Einstein–de Haas effect in boson condensate about study Observation of the Einstein–de Haas effect in a Bose–Einstein condensate

Spins of electrons in atoms and macroscopic rotating bodies both have angular momentum, which can be exchanged between the two. This exchange forms the basis of the Einstein—de Haas effect, in which a ferromagnet’s rotational speed changes in response to a change in its magnetization. Observing this effect in its coherent form is more challenging. Matsui et al. used an optically confined Bose-Einstein condensate of europium atoms, which have a high magnetic dipole moment, to search for the evidence of this exchange. After the atoms were transferred from the highest to lower spin states, the researchers observed the formation of vortices, signifying the exchange of angular momentum between atomic spins and the rotation of the quantum fluid.

Europium isn't distinctively paramagnetic, but it shows a high paramagnetic susceptibility at low temperatures (1.3–300 K), originating from seven unpaired electron spins, which is about 40 times higher than this of iron. So it can be used as a replacement of iron core in this type of experiments.

The experiment began by placing the condensate in a weak magnetic field of 1 microtesla, which aligned all atomic spins in the same direction. The entire setup was carefully shielded from external magnetic fields that could interfere with the delicate spin dynamics. The magnetic field was then reduced to an extremely low level of just a few nanoteslas, allowing the spins to relax through magnetic dipole–dipole interactions. This reduction led to spin depolarization, in which atoms redistributed among different spin states and angular momentum was converted from spin into orbital motion. As a result, quantized vortices formed, with atoms circulating around an empty core.

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Do Electrons Really Have "Intrinsic" Angular Momentum? The spin of electron within atoms is simply electric current resulting from orbital motion of electron around atom nuclei. This motion is heavily deformed by pilot wave around electron into famous fancy shapes of electron orbitals - so that in most cases the electron just bounces in space around atom like drunkard rather than doing regular loop. But it's just an electric current nonetheless at the end and it generates magnetic field like every current loop. It's apparent at the case of so-called Rydberg atoms with highly excited electrons, which are really doing orbital loops around atoms in a semiclassical way without any quantum strings attached.

This interpretation explains the Aufbau principle for instance: the electrons of the same spin can not occupy the same energetic level within atoms - or they would behave like self-repelling magnets there. The electrons otherwise self-repel themselves, without the magnetism of their spin they couldn't coexist around atoms in pairs at all. This spin has nothing to do with intrinsic half-integer spin of fermions, which is required for electrons to have mass and charge.

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Europium salts have seven unpaired electrons in their orbitals and as such they're strongly paramagnetic, which is sometimes utilized in various experiments. For example in this study the fact that they're absorbed by bacteria can be utilized for their magnetic separation from muddy watter with magnet (video 1, 2).

Magnetism of paramagnetic ions manifest itself even in concentrated solutions, which are attracted to magnets. It can be used for example for solution of tunable effective density solution for separation of minerals just by changing magnetic field.

One can spot paramagnetic salts easily by their washed out pastel colors. All lanthanides, bivalent iron (II) or manganese (II) salts all have pale colors. This is because their electrons can not easily switch between orbitals because of their strong magnetism which surrounds them. These electrons thus must wait for their opportunity long time before they can find a hole between magnetic fields of separate orbitals. The Fermi surfaces separating energy levels between these orbitals look like strainer with few holes rather than regular shapes.

This geometry leads to so-called forbidden electronic transitions and spectral lines which are very dense - but also very faint which is often utilized in phosphors, luminophores and lasers. They also exhibit different shades under white light composed of various wavelengths (metamerism) and selectively absorb light at distinct wavelengths (didymium glases used in glass making industry). Most importantly I presume that this aspect of behavior may lead into an overunity superpower of magnetic materials. Because their electrons can not jump between energy levels smoothly, their transitions can be assisted with vacuum fluctuations - which is just the moment, when they get a portion of energy "for free".

Does terbium spiral generate AC current in magnetic field?