Zenith Grant Awardee

Dr. Dmitry Budker

University of California at Berkeley

Co-Investigators

Arman Cingoz, <i>UC Berkeley</i><br>Nathan Leefer, <i>UC Berkeley</i>

Project Title

A Laboratory Search for Temporal and Spatial Variation of the Fine-Structure Constant Using Atomic Dysprosium

Project Summary

Our understanding of the physical universe relies on theories containing "fundamental constants," quantities, such as speed of light, that are measured in laboratories but cannot be predicted from theoretical considerations alone. These constants are considered fundamental because they set certain important scales in physics, and appear ubiquitously in many unrelated branches of physics. While current theories assume these quantities to be constant, it is important to check this assumption by searching for spatial and temporal variation of fundamental constants. Recently, astrophysical observations indicate that one such constant, the fine-structure constant (alpha), might be changing over the lifetime of the universe. Alpha dictates the strength of interactions between light and matter, and critically determines the wavelength of the light emitted or absorbed by atoms. We propose a search for a change of alpha of a few parts in one billion billion per year by investigating small temporal variations in the wavelength of radio waves absorbed by atoms of dysprosium exceptionally sensitive to alpha variation. Discovery of alpha variation would indicate new physics beyond current models: for example, it would contradict Einstein's theory of relativity and could be a signature of extra space-time dimensions or additional fundamental forces.

Technical Abstract

We propose a laboratory search for temporal variation of the fine-structure constant, α, exceeding the sensitivity level of quasar-absorption searches and current atomic-clock laboratory measurements by two orders of magnitude. The experimental technique utilizes radio-frequency (rf) spectroscopy of electric-dipole transitions between nearly degenerate opposite-parity electronic levels in atomic dysprosium that are highly sensitive to α variation. Measurements with an existing atomic-beam rf spectrometer have reached a sensitivity of ~ 2 x10^-15 yr^-1. The investigation of systematic uncertainties with this apparatus has solidified the design criteria for a new apparatus, expected to reach a sensitivity to the fractional α variation of ~ 10^-18 yr^-1. Moreover, the data obtained for the temporal variation of α can be used to constrain possible variation of α with a changing gravitational potential since, during the data acquisition period, the Earth is located at different values of the gravitational potential of the Sun. Data obtained with the existing apparatus have constrained such variation at a level of 1.5 x 10^-5. The proposed second-generation apparatus is expected to reach a limit of 10^-8, providing one of the most stringent test of this type for Einstein's equivalence principle.