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- Heidelberg, Germany—Scientists at the Max Planck Institute for nuclear Physics (MPIK) have achieved a significant milestone in testing quantum electrodynamics (QED), the theory describing electromagnetic phenomena.
- QED stands as one of physics' most precisely tested theories.
- The electron's g-factor, relating its spin and magnetic properties, offers a prime testing ground for QED.
quantum Electrodynamics Tested with Lithium-like Tin: Precision Measurement Refines QED Theory
Heidelberg, Germany—Scientists at the Max Planck Institute for nuclear Physics (MPIK) have achieved a significant milestone in testing quantum electrodynamics (QED), the theory describing electromagnetic phenomena. Their work, focusing on the bound electron g-factor in lithium-like tin, reached an experimental accuracy of 0.5 parts per billion.
QED stands as one of physics’ most precisely tested theories. Physicists continually seek to push its boundaries, as any deviation could signal new physics. The theory explains electromagnetic interaction as the exchange of virtual photons between charged particles. These interactions include electrons “talking” to each other and the nucleus, and with themselves via self-energy.
The electron’s g-factor, relating its spin and magnetic properties, offers a prime testing ground for QED. While Dirac’s theory predicts a g-factor of exactly 2 for a free electron, QED interactions cause slight deviations. These effects intensify in strong electric fields, such as those experienced by electrons near heavy nuclei.
The MPIK team’s experiment examined lithium-like tin, similar to hydrogen but with two additional inner-shell electrons. This system allows scientists to probe interelectronic QED effects.
The theoretical prediction for the g-factor reached a precision of 6 parts per billion, using an enhanced interelectronic QED method. This “from the beginning” calculation accounts for electromagnetic interactions among the ion’s constituents,including QED effects. electron structure and QED screening effects are also incorporated.
The experimental value obtained for the g factor of the lithium-like tin ion is gexp = 1.980 354 799 750(84)stat(54)sys(944)ext, with statistical, systematic, and external uncertainties detailed.The measurement was conducted using the cryogenic Penning trap ALPHATRAP at MPIK. The strong magnetic field inside the trap causes the ion to move in a characteristic way,and the outer electron’s spin to precess.
Researchers persistent the g factor by measuring the ratio of the ion’s motional frequency to its precession frequency, eliminating the magnetic field from the calculation. Microwave radiation induced spin flips, revealing the precession frequency.
gth = 1.980 354 797(12)
The experimental result aligns with the theoretical prediction within the calculation’s uncertainty. The team says that improving the precision of the ion mass value could further enhance the precision of the g factor.
What’s next
Future research will focus on heavier lithium-like systems, such as 208Pb79+, coupled with advancements in two-loop QED calculations. This will provide even more rigorous tests of QED in strong electric fields.The theoretical methods developed can also be applied to more complex ions and other effects.