Hudson Abstract

"Investigation of the optical transition in the 229Th nucleus: Solid‐state optical frequency standard and fundamental constant variation"

Eric R. Hudson, Department of Physics and Astronomy, UCLA

The technological impact of atomic clocks has been profound, ranging from the successful implementation of global positioning systems and cellular telephones to the synchronization of modern‐day electrical power grids. Improved clocks, based on optical frequency standards, are likely to have real‐world utility at an even greater level. Furthermore, high‐precision clocks have provided a means to probe fundamental issues in physics. For example, atomic clock experiments have provided some of the most stringent tests of General Relativity [1]. Because of these motivations, there is presently enormous effort towards building next‐generation atomic clocks. It appears universally recognized that the most promising route to improved clocks uses reference oscillators based on optical transitions [2‐5]. Indeed, several optical atomic clock experiments have already reported better stability than the primary Cesium standard [4, 5].

We have recently described a novel optical frequency standard [6]. Based on a high‐Q transition in the 229Th nucleus, this “nuclear” clock architecture promises up to six orders of magnitude improvement in precision over next‐generation optical atomic clocks, while simultaneously reducing experimental complexity. This paradigm shift in optical frequency standards is possible because, as indicated by recent data [7], the 229Th transition has the lowest energy of any known nuclear excitation, making it amenable to study by laser spectroscopy. Furthermore, because nuclear energy levels are relatively insensitive to their environment, the complicated vacuum apparatus of current optical frequency standards can be replaced by a single crystal doped with 229Th atoms.

In addition to its attractive properties as a frequency standard, our proposed system opens the possibility for even more dramatic improvements in sensitivity to address one of the most interesting questions in fundamental physics: are the constants of nature actually constant?Recent astrophysical measurements have hinted at possible fundamental constant variation over cosmological time [8‐10]. Moreover, current theories that attempt to unify gravity with the other fundamental forces can lead to spatial and temporal variations in the fundamental constants [11], e.g. the fine structure constant . These theories can include space‐time with extra dimensions of variable geometry, and/or light scalar fields whose variable amplitude couples to ordinary matter. Both effects can change the apparent values of constants. Light scalar fields are potential candidates, dubbed “quintessence”, to explain the observed dark energy that dominates the universe. Thus, sensitive probes for possible variation of fundamental constants provide an important means to constrain these models which are extensions to the Standard Model.

I will discuss the details of the “nuclear” clock architecture and our progress towards its implementation. If time allows, I will also discuss a new experimental effort at UCLA [12] for the production and study of ultracold molecular ions.

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