Testing three-body quantum electrodynamics with trapped Ti20+ ions: evidence for a Z-dependent divergence between...

Area of Science:

• Atomic Physics
• Quantum Electrodynamics
• Spectroscopy

Background:

• Quantum electrodynamics (QED) is a fundamental theory describing interactions between light and matter.
• Heliumlike ions provide sensitive probes for testing QED due to their simple electronic structure.
• Previous tests have primarily focused on one-electron contributions, with fewer experiments probing two-electron QED effects.

Purpose of the Study:

• To conduct a new, precise test of QED by measuring the w (1s2p(1)P(1)→1s(2)(1)S(0)) x-ray resonance line transition energy in heliumlike titanium.
• To investigate systematic discrepancies between QED theory and experimental data for heliumlike ions across a range of atomic numbers (Z).

Main Methods:

• Utilized an electron beam ion trap to confine and strip titanium atoms.
• Employed a curved-crystal spectrometer calibrated with absolute wavelength standards to minimize Doppler shifts and ensure accurate measurements.
• Measured the transition energy of the w x-ray resonance line in heliumlike titanium.

Main Results:

• The measured transition energy for the w line in heliumlike titanium is 4749.85(7) eV.
• This experimental result deviates from the latest ab initio QED prediction by three times the experimental uncertainty.
• A systematic discrepancy, growing as approximately Z(3), was observed between QED theory and experimental data for heliumlike ions with Z>20, reaching 5 standard deviations.

Conclusions:

• The study presents a new, precise experimental test of QED in heliumlike titanium.
• The findings highlight a significant, Z-dependent discrepancy between state-of-the-art QED calculations and experimental data for heavier heliumlike ions.
• Further theoretical and experimental work is needed to resolve the observed divergence and refine our understanding of QED in multi-electron systems.