Investigation of the fine structure of antihydrogen

Abstract

At the historic Shelter Island Conference on the Foundations of Quantum Mechanics in 1947, Willis Lamb reported an unexpected feature in the fine structure of atomic hydrogen: a separation of the 2S1/2 and 2P1/2 states1. The observation of this separation, now known as the Lamb shift, marked an important event in the evolution of modern physics, inspiring others to develop the theory of quantum electrodynamics2–5. Quantum electrodynamics also describes antimatter, but it has only recently become possible to synthesize and trap atomic antimatter to probe its structure. Mirroring the historical development of quantum atomic physics in the twentieth century, modern measurements on anti-atoms represent a unique approach for testing quantum electrodynamics and the foundational symmetries of the standard model. Here we report measurements of the fine structure in the n = 2 states of antihydrogen, the antimatter counterpart of the hydrogen atom. Using optical excitation of the 1S–2P Lyman-α transitions in antihydrogen6, we determine their frequencies in a magnetic field of 1 tesla to a precision of 16 parts per billion. Assuming the standard Zeeman and hyperfine interactions, we infer the zero-field fine-structure splitting (2P1/2–2P3/2) in antihydrogen. The resulting value is consistent with the predictions of quantum electrodynamics to a precision of 2 per cent. Using our previously measured value of the 1S–2S transition frequency6,7, we find that the classic Lamb shift in antihydrogen (2S1/2–2P1/2 splitting at zero field) is consistent with theory at a level of 11 per cent. Our observations represent an important step towards precision measurements of the fine structure and the Lamb shift in the antihydrogen spectrum as tests of the charge–parity–time symmetry8 and towards the determination of other fundamental quantities, such as the antiproton charge radius9,10, in this antimatter system.

History and Some Aspects of the Lamb Shift

“…Another topic of significant current interest is the Lamb shift in antihydrogen. The measurements to date agree with theory at a level of 11% [93]. These results serve as tests for charge-parity-time symmetry and as a determination of the anti-proton radius.…”

Early Universe Plasma Separation and the Creation of a Dual Universe

“…In contrast with the ΛCDM assumption of antimatter elimination, the matter and antimatter in the plasma could be separated by electromagnetic fields (Klein, 1966(Klein, , 1971 due to the plasma drift phenomenon, consequently, evolving in opposite directions. This scenario corresponds the CMB dipole anisotropy and the quantum electrodynamics theory (QET), where advanced measurements of the fine structure of hydrogen and antihydrogen atoms were found to be consistent with predictions of QET with a precision of 2%, including the Lamb shift feature (Ahmadi et al, 2020). These measurements corroborate the concept of identical matter and antimatter apart of their opposite charge and spin, which can undermine the elimination assumption.…”

Laser cooling of antihydrogen atoms

“…To realize this goal, we have developed a novel, solid-state-based, pulsed Lyman-α laser 28 , and previously used it to probe the 1S–2P transition in trapped antihydrogen 10 and to observe the fine structure and the Lamb shift 11 . These studies established our capability to precisely drive and detect the Lyman-α transition with single-atom sensitivity.…”

“…Here we demonstrate laser cooling of antihydrogen 9 , the antimatter atom consisting of an antiproton and a positron. By exciting the 1S–2P transition in antihydrogen with pulsed, narrow-linewidth, Lyman-α laser radiation 10 , 11 , we Doppler-cool a sample of magnetically trapped antihydrogen. Although we apply laser cooling in only one dimension, the trap couples the longitudinal and transverse motions of the anti-atoms, leading to cooling in all three dimensions.…”

“…The demonstration of laser cooling and its immediate application has far-reaching implications for antimatter studies. A more localized, denser and colder sample of antihydrogen will drastically improve spectroscopic 11 – 13 and gravitational 14 studies of antihydrogen in ongoing experiments. Furthermore, the demonstrated ability to manipulate the motion of antimatter atoms by laser light will potentially provide ground-breaking opportunities for future experiments, such as anti-atomic fountains, anti-atom interferometry and the creation of antimatter molecules.…”