Advancing the theory of the hydrogen atom. (News Briefs).

The hydrogen atom is the most basic atom from the point of view of atomic structure theory. Historically, efforts to understand its detailed properties have led to many advances in understanding fundamental physics. This atom is important not only as a model system that tests the limits of atomic theory and experiment, but it also provides information on fundamental physical constants, such as the Rydberg constant. In the past decade, the precision of the experiments has been improving rapidly, and improvements in the theory have been necessary to keep pace.

Over the past several years, a NIST-led project has carried out a precise calculation of the most basic quantum electrodynamic (QED) effect in the spectrum of hydrogen, namely the radiative process in which the atom emits and then reabsorbs a photon (the quantum of electromagnetic radiation). This process results in shifts of the atomic energy levels, which, in turn, affect the frequencies of light that are emitted and absorbed in experiments. The NIST work has led to a reduction of the uncertainty in the one-photon QED effect by over three orders of magnitude.

This accomplishment was made possible by a number of factors, including the high-performance computing resources at NIST and new developments in numerical analysis. The calculation required months of intensive, high-performance parallel computation.

This project was a collaboration between NIST, the Technical University of Dresden, and the University of Regensburg, both in Germany. The results have received wide recognition. For example, the project has been described as a "spectacular success" in Physics Reports, Vol. 342, p. 63 (2001).

CONTACT: Peter Mohr, [phone]; [e-mail].