JAPC - Investigation of the optical transition in the ²²⁹Th nucleus

Speaker: Prof. Eric Hudson, University of California, Los Angeles

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

Time: 2:00 PM, Friday, November 6th, 2009

Place: P-148 (refreshments will be served at 1:30 PM in P145A)

Abstract: One of the most interesting questions in fundamental physics is: are the constants of nature actually constant? Recent astrophysical measurements have hinted at possible fundamental constant variation over cosmological time [1‐3]. Moreover, current theories that attempt to unify gravity with the other fundamental forces can lead to spatial and temporal variations in the fundamental constants [4], 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.

We have recently described a novel optical frequency standard [5] that exhibits extreme sensitivity to several fundamental constants. Based on a high‐Q transition in the ²²⁹Th nucleus, this "nuclear" clock architecture promises orders of magnitude improvement in sensitivity over current experiments [6], 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.

I will discuss the history of the search for fundamental constant variation, the details of the "nuclear" clock architecture, and our progress towards its implementation.

1. J. K. Webb et al., Phys. Rev. Lett. 87, 091301 (2001).
2. R. Quast, D. Reimers, and S. Levshakov, Astron. Astrophys. 415, L7 (2004).
3. E. Reinhold, et al., Phys. Rev. Lett. 96 151101 (2007).
4. K. Olive and Y. Qian, Phys. Today 57, No. 10, 40 (2004).
5. W.G. Rellergert et al., arXiv: 0905.2230 (2009).
6. T. Rosenband et al., Science 319, 1808 (2008).
7. B.R. Beck et al., Phys. Rev. Lett. 98, 142501 (2007).

Hosted by: Prof. Michael Bromley.

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