December 12, 2005
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AMHERST, Mass.—Larry Hunter, the Stone Professor of Natural Science (Physics) at Amherst College, recently had an article on “Measurement of the Electron Dipole Moment Using GdIG” accepted for publication in Physical Review Letters, the journal of the American Physical Society, on Dec. 16.

“Time reversal violation,” Hunter says, “remains one of the most fascinating elements of modern physics. The preponderance of matter in the universe seems to call for new kinds of physics, beyond the standard model, a physics that violates the irreversibility of time. Looking for the permanent electric dipole moment of a fundamental particle is highly sensitive to such time reversal violation.” An electric dipole moment is a charge distribution characterized by the distance that separates positive and negative charges; in a charged particle like the electron, it can be thought of as the distance between the center of mass and the center of charge. This experiment has shown that for the electron this distance must be smaller than 5 x 10E^-24 cm. This distance is more than 10 billion times smaller than a proton radius.

Thus far, no permanent electric dipole moment of any fundamental particle has been observed. Hunter and his team have investigated a new technique for the measurement of the electric dipole moment of the electron, using gadolinium iron garnet (GdIG). The physicists apply a magnetic field to a GdIG sample and sensitively look for the predicted voltage across it. “With this method,” Hunter reports, “we have improved the limits obtained on the electron edm from a solid by a factor of 40. We have also identified the primary obstacle to further improvement of the method. If this obstacle can be overcome, experiments of this design may eventually achieve sensitivities to the electron edm beyond those obtained with atomic beams.”

David DeMille, a professor of physics at Yale University, says, “This innovative work opens an exciting new angle of attack on a problem which is one of the hottest topics in physics now. As always, the work of Hunter and his colleagues is thorough and insightful.”

Hunter shares authorship with current and former Amherst College students Ben Heidenreich ’06 (East Corinth, Vt.), Oliver T. Elliot ’03, Noah Charney ’02, Kyle Virgien ’08 (Los Angeles, Calif.), Alexander Bridges ’07 (Ponte Vedra, Fla.), Maggie A. McKeon ’05; as well as Stephen A. Peck, a postdoctoral fellow at Amherst; Dan Krause, Jr., the head of the machine shop; and Joel Gordon, the Stone Professor of Natural Science (Physics) Emeritus at Amherst. S.K. Lamoreaux of the Los Alamos National Laboratory, Physics Division, was a co-author of the study, sponsored by Los Alamos, Amherst College, the National Science Foundation and the Howard Hughes Foundation.

A member of the Amherst faculty since 1983, Hunter has been engaged in a wide variety of research activities. His longest running experiment has been a search for an electron electric-dipole moment. He received the 1990 APS Award for Research at an Undergraduate Institution, and in 1994 served as chair of the APS Precision Measurement and Fundamental Constants topical group. A Fellow of the American Physical Society, Hunter received a B.A from Columbia University and M.A. and Ph.D. degrees from the University of California, Berkeley.