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Effects of Configuration Interaction on Intensities and Phase Shifts

David R. Lide

Published Feb 6, 2018• 3 citations

Abstract

One of the enduring goals of scientific work at the National Institute of Standards and Technology (NIST) has been the expression of measurements in terms related directly to natural phenomena of an invariant and absolute character. Ugo Fano is believed to be the first theoretical physicist hired by NIST, and he has certainly been one of the most influential to date. His 1961 paper Effects of Configuration Interaction on Intensities and Phase Shifts is one of the most frequently referenced journal articles by a NIST author, having been cited over 3200 times in the scientific literature. This paper treats a subject of fundamental interest to metrology and physics: the excitation spectra of quantum-mechanical systems. Exponential decay is encountered in a number of physical systems, such as the natural transmutation of radioactive elements. An alternative mode of observation of exponential decay is the resolution of its frequency spectrum.

DOI: 10.1201/9781351069397-33

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Abstract William Phillips of the National Institute of Standards and Technology (NIST) in Gaithersburg, Maryland, shared the 1997 Nobel Prize in physics for his work in developing laser methods for cooling and trapping atoms. Interactions between the light field and the atoms create what is dubbed an ‘optical molasses’ that slows the atoms down, thereby reducing their temperature to within a fraction of a degree of absolute zero. These techniques allow atoms to be studied with great precision, for example measuring their resonant frequencies for light absorption very accurately, so that these frequencies may supply very stable timing standards for atomic clocks. Besides applications in metrology, such cooling methods can also be used to study new fundamental physics. The 1997 Nobel award was widely considered to be a response to the first observation in 1995 of pure Bose–Einstein condensation (BEC), in which a collection of bosonic atoms all occupy a single quantum state. This quantum-mechanical effect only becomes possible at very low temperatures, and the team that achieved it, working at JILA operated jointly by the University of Colorado and NIST, used the techniques devised by Phillips and others. Since then, cold-atom physics has branched in many directions, among them being attempts to make a quantum computer (which would use logic operations based on quantum rules) from ultracold trapped atoms and ions. ‘National Science Review’ spoke with Phillips about the development and future potential of the field.

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Our ability to study the interactions between atoms at ultracold temperatures has undergone little short of a revolution in recent years. This is largely due to the development of spectroscopic techniques that can probe the properties of laser-cooled atoms with high precision. One of these techniques is photoassociation, and a group at the National Institute of Standards and Technology (NIST) in Maryland, US, has now used this method to obtain new information about the interactions between atoms in molecules. The NIST researchers used lasers to produce and probe pairs of sodium atoms that were bound together in very long-range molecular states (K M Jones et al. 1997 J. Phys. B.30289).