Quantum electrodynamics has been tested 100 times more precisely than ever before

Quantum mechanics

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Using a newly developed technique, scientists at the Max Planck Institute for Nuclear Physics (MPIK) in Heidelberg have measured the tiny difference in the magnetic properties of the two isotopes of high-charge neon in an ion trap with previously inaccessible precision. Comparison with highly accurate theoretical calculations of this difference allows testing of a standard quantum electrodynamics (QED). The concordance of the results is an impressive confirmation of the Standard Model of physics, allowing conclusions about the properties of nuclei and setting limits for new physics and dark matter.

Electrons are some of the basic building blocks of matter as we know it. It has some very special properties, such as its negative charge and the presence of a very specific intrinsic angular momentum, also called spin. As a charged particle with a spin, each electron has a magnetic moment that aligns itself in a magnetic field similar to a compass needle. The strength of this magnetic moment, given by the so-called g-factor, can be predicted with extraordinary accuracy Quantum electrodynamics. This calculation agrees with the experimentally measured g-factor in the order of 12 digits, and is one of the most accurate matches for theory and experiment in physics to date. However, the magnetic moment of the electron changes once it is no longer a “free” particle, that is, unaffected by other influences, but is instead bound to the nucleus of an atom, for example. Small changes in the g-factor can be calculated by means of QED, which describes the interaction between the electron and the nucleus in terms of the exchange of photons. High-precision measurements allow sensitive testing of this theory.

“Through our work, we have now succeeded in investigating these QED predictions with unprecedented accuracy and, in part, for the first time,” reports group leader Sven Sturm. “To do this, we looked at the difference in the g-factor for two isotopes of highly charged neon ions that possess only one electron.” These are similar to hydrogen, but with a nuclear charge 10 times higher, which enhances the effects of QED. Isotopes differ only in the number of neutrons in the nucleus when the nuclear charge is the same. 20Ne9+ And the 22Ne9+ With 10 and 12 neutrons respectively.

The ALPHATRAP experiment at the Max Planck Institute for Nuclear Physics in Heidelberg provides a custom-designed Penning trap that stores single ions in a strong magnetic field of 4 Tesla in a nearly perfect vacuum. The objective of the measurement is to determine the energy required to flip the direction of the “compass needle” (rotation) in the magnetic field. To do this, the exact frequency of microwave excitation required for this purpose is searched. However, this frequency also depends on the exact value of the magnetic field. To determine this, the researchers exploit the movement of ions in the Penning trap, which also depends on the magnetic field.

Despite the very good temporal stability of the superconducting magnet used here, small, unavoidable fluctuations in the magnetic field limit the previous measurements to about 11 digits of accuracy.

The idea of ​​the new method is to store the ions to be compared, 20Ne9+ And the 22Ne9+ At the same time in the same magnetic field in a double motion. In such a movement, two ions They always rotate opposite each other on a common circular path with a radius of only 200 μm,” explains Fabian Heiße, Postdoc in the ALPHATRAP experiment.

As a result, magnetic field fluctuations have practically identical effects on both isotopes, so there is no effect on the difference in energies being sought. Combined with the measured magnetic field, the researchers were able to determine the difference in g-factors for both isotopes with a standard accuracy of 13 digits, a 100-digit improvement over previous measurements, and thus the most accurate comparison of the two g-factors worldwide. The accuracy achieved here can be illustrated as follows: if the researchers, instead of the g-factor, measure Germany’s highest mountain, the Zugspitze, with this precision, they would be able to identify individual additional atoms on the summit by the height of the mountain.

Theoretical calculations were performed with similar precision in the Christoph Keitel department at MPIK. “By comparison with the new experimental values, we confirmed that the electron is indeed interacting with the atomic nucleus via the exchange of photons, as predicted by QED,” explains group leader Zoltan Haarmann. This has now been solved and successfully tested for the first time by difference measurements on the two isotopes of neon. Alternatively, assuming that the QED results are known, the study allows the nuclear radius of isotopes It is determined more precisely than previously possible by a factor of 10.

“On the contrary, the agreement between the results of theory and experiment allows us to constrain the new physics beyond the well-known Standard Model, such as the strength of the ion’s interaction with dark matter,” says postdoctoral researcher Vincent Depierre.

“In the future, the method presented here could allow for a number of exciting new experiments, such as direct comparison of matter and antimatter or very precise determination of the fundamental constants,” says first author Dr. Tim Seiler.


Study the magnetic properties of helium 3


more information:
Tim Sailer et al, Measurement of the electron-bound g-factor difference in paired ions, temper nature (2022). DOI: 10.1038 / s41586-022-04807-w

the quote: Quantum electrodynamics tested 100 times more accurately than ever before (2022, June 15) Retrieved on June 16, 2022 from https://phys.org/news/2022-06-quantum-electrodynamics-accurately.html

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