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Zenith Grant Awardee

Dr. Ekkehard Peik



Christian Tamm, <i>PTB</i><br>Burghard Lipphardt, <i>PTB</i>

Project Title

Laborotory Search for a temporal variation of the fine structure constant

Project Summary

While we know that the universe is expanding and evolving, the basic theories of physics assume invariable parameters, called the fundamental constants. Prominent examples are the speed of light, the elementary charge and the so-called fine-structure constant alpha, a number that appears in many electric and atomic phenomena. We will perform a very precise experimental test of the constancy of alpha by comparing two special atomic clocks based on different atomic frequencies: If alpha would change in time, these clocks would slowly drift out of synchronism. There are astronomical observations that seem to indicate that a few billion years ago alpha may have varied significantly. If that rate of change persists until today, the effect would show up in our clock comparison experiment within a measuring time of one year only. An unequivocal observation of the temporal drift of a fundamental constant would refute a basic postulate and would thus force us to rethink the fundamental theories of physics.

Technical Abstract

We propose a laboratory search for the possible temporal variation of the fine structure constant alpha in the present epoch. The experiment is based on the repeated measurement of the frequency ratio of two forbidden optical transitions originating form the ground state of the Yb+ ion: the S-D quadrupole line at 688 THz and the S-F octupole line at 642 THz. Because of the large relativistic contributions to the level energies, these two transition frequencies would react very sensitively and with opposite sign to a change of the fine structure constant. Using the techniques of high-resolution spectroscopy of trapped and laser-cooled ions and the recently developed femtosecond laser frequency comb generator for the optical frequency ratio measurement we expect to determine the frequency ratio with a relative uncertainty of 5E-16. This would allow us to search for relative changes of alpha at the level of 1E-16 per year within a period of only one year. Recent astrophysical observations seem to indicate a change of alpha of 5E-6 over a cosmological timescale of 1E10 years.

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