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Measuring the Magnet in the Electron

Gerald Gabrielse '73, Leverett Professor of Physics at Harvard University
March 11, 2011, 2:30pm, North Hall 078

Harvard physicist and Calvin graduate Gerald Gabrielse gained international fame for trapping entire atoms of antimatter and for measuring properties of electrons with unprecedented precision. He will talk about some of his prizewinning work: “Measuring the Magnet in the Electron.” Having taught in high school as well as at Harvard, Dr. Gabrielse is adept at explaining his extraordinary work to a diverse audience. Afterwards current and prospective students are invited to meet with Dr. Gabrielse over pizza to talk with him about his work, about careers in physics, or about how he relates physics to his Christian faith.

Abstract: The electron is one of the particles from which we and much of the universe are made, along with the proton and neutron.  Remarkably, it has no size that we have been able to measure.   It also has "spin" though nothing mechanical is rotating.  And, because of its interaction with empty space (because empty space is only empty on average) it behaves as if it has a bar magnet located within itself.  Using experimental methods that I started learning in the basement of the Calvin College science building, my students and I are now able to suspend a single electron by itself for months at a time while we measure the size of the magnet within the electron.   The electron suspended in a delicately engineered apparatus acts like a homemade, artificial atom with quantized energy levels.   With the apparatus cooled within a tenth of a degree of absolute zero, with very sensitive cryogenic electronics, and with extensive computer interfacing, we are able to observe and cause the occasional "quantum jump" between the electron's energy levels.   From the rate of these jumps we deduce the size of the electron's magnet to an unusual precision of 3 parts in 10^{13}.  Quantum electrodynamics theory can calculate this magnetic moment almost as accurately as we can measure, and the comparison of theory and experiment is arguably the most precise such comparison ever made.

Cylindrical Penning Trap made by Gabrielse group


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