Quantum Electrodynamics of Atomic Systems and Interactions

Quantum electrodynamics (QED) provides the rigorous framework for understanding how charged particles interact via the exchange of photons. In atomic systems, bound-state QED accounts for subtle shifts in energy levels arising from vacuum polarisation, electron self-energy and photon-exchange effects. These radiative corrections give rise to phenomena such as the Lamb shift and hyperfine splitting, which have shaped our understanding of the hydrogen spectrum and underpinned precise determinations of fundamental constants. Advances in laser and muonic-atom spectroscopy now probe QED at unprecedented precision, testing higher-order corrections and revealing the influence of nuclear structure. Molecular ions and exotic atoms extend these tests to multi-body systems, enabling deep insights into the interplay between electromagnetic theory and nuclear dynamics. The interplay of theory and experiment in bound-state QED continues to refine the values of the fine-structure constant, proton and α-particle charge radii, and to constrain possible new physics beyond the Standard Model. Emerging techniques in trap-based spectroscopy and high-field measurement are set to push the boundaries of QED tests further, with implications for metrology, fundamental symmetries and the search for weakly coupled forces at sub-Ångström scales.

Research from Nature Portfolio

Recent studies have demonstrated the power of precision spectroscopy in testing bound-state QED at the molecular level. Measurements of a vibrational overtone transition in the molecular hydrogen ion have reached agreement between theory and experiment at the parts-per-billion level, confirming high-order QED calculations and enabling improved determinations of the proton-to-electron mass ratio. Complementing this, laser spectroscopy of muonic helium-4 ions has yielded two‐photon 2S–2P transition frequencies that determine the α-particle root-mean-square charge radius with sub-femtometre precision. These results not only benchmark few-nucleon theories and lattice quantum chromodynamics but also constrain proposals for physics beyond the Standard Model and validate the consistency of nuclear dimension measurements across different atomic systems.

Quantum Electrodynamics of Atomic Systems and Interactions publication trend

The graph below shows the total number of articles in quantum electrodynamics of atomic systems and interactions across all publications each year (not limited to Nature Index journals).

Technical terms

Quantum electrodynamics (QED): The quantum field theory describing interactions of charged particles and photons, including radiative corrections to energy levels.

Bound-state QED: The application of QED to particles confined in atomic or molecular potentials, accounting for vacuum polarisation and self-energy shifts.

Lamb shift: A small energy difference between atomic s and p orbital levels arising from vacuum fluctuations and electron self-energy.

Hyperfine splitting: The division of atomic energy levels due to interactions between electron and nuclear magnetic moments.

Muonic atom: An exotic atom in which one electron is replaced by a heavier muon, amplifying sensitivity to nuclear structure effects.

Vibrational overtone transition: A higher-order molecular transition involving changes in vibrational quantum number, used for precision spectroscopy.

References

1. Probing QED and fundamental constants through laser spectroscopy of vibrational transitions in HD+. Nature Communications (2016).
2. Measuring the α-particle charge radius with muonic helium-4 ions. Nature (2021).
3. Three-body QED test and fifth-force constraint from vibrations and rotations of HD+. Physical Review Research (2021).
4. Chiral perturbation theory of muonic-hydrogen Lamb shift: polarizability contribution. European Physical Journal C (2014).
5. The two-photon exchange contribution to muonic hydrogen from chiral perturbation theory. Nuclear Physics B (2014).