Hans Dehmelt Biography (1922-)


Hans Dehmelt has devoted his career as a physicist to developing means of performing highly precise, accurate atomic measurements. In pursuit of this goal, Dehmelt devised a trap that for the first time isolated a single electron,which in turn made possible the precise experimental measurements that verified the theory of quantum electrodynamics. For his work, Dehmelt was honored with a share in the 1989 Nobel Prize in physics.

The son of Georg Karl and Asta Ella Klemmt Dehmelt, Hans Georg Dehmelt was born on September 9, 1922, in Görlitz, Germany. An early interest in the workings of radios led Dehmelt to the study of physics, which was interruptedby service in the German army and a period as a prisoner of war in France during World War II. After the war, Dehmelt continued his studies in physics atthe University of Göttingen, financing himself in part by repairing broken radios. During one college course, Dehmelt became interested in the possibility of isolating the electron, something theorists said couldn't be done.

Dehmelt earned his Ph.D. from Göttingen in 1950 and stayed on for postdoctoral work until 1952, concentrating on nuclear magnetic resonance, and using his skill in electronics to make up for a postwar lack of conventional experimental equipment. He continued these studies from 1952 to 1955 at Duke University in the United States, and became a professor at the University of Washington in 1955, where he remains today. While at Washington, Dehmelt returnedto his original interest in isolating the electron in order to measure it accurately. Although the electron's mass and charge could be measured preciselywith existing methods, its spin and magnetism could not be. Quantum electrodynamics (QED) did predict the electron's spin and magnetism, as part of QED'sexplanation of all interactions between electrically charged particles, butuntil spin and magnetism were actually measured on existing electrons, QED remained an unproven theory.

In 1959, Dehmelt's electronics background once again came into play. He usedan electronic component called a Penning discharge tube to build what he called a Penning trap: a vacuum tube with a strong magnetic field and a weak electric field that trapped and held electrons. Throughout the 1960s Dehmelt andhis colleagues tried to devise ways of measuring the gyromagnetic ratio, or g-factor, of an electron, which had been calculated theoretically via quantum mechanics. Dehmelt and his team found that by manipulating voltage, they could drive electrons out of the trap until only a single one remained. This breakthrough was accomplished in 1973, and soon the team was able to capture and hold single electrons for extended periods of time. Two years later, Dehmelt worked out a way to cool the trapped electron, which slowed its motionand made accurate measurement easier. In 1976 Dehmelt and his coworkers usedtheir trap to observe the quantum jump of a single ion, again confirming a prediction of quantum mechanics.

Soon Dehmelt and his team were able to measure the g-factor to ten times its previously calculated value. Driven by his goal for ever more accurateatomic measurements, Dehmelt applied a number of refinements to his trap sotheg-factor could be measured to 12 decimal places by 1991. Dehmelt and his colleagues have also trapped positrons (antielectrons). One of these positrons, which he named Priscilla, was held for three months, performing itsquantum jumps and thus allowing the first experimental measurement of the g-factor for antimatter. Dehmelt also initiated and guided an experimentat the University of Heidelberg in 1974 to trap and observe a single barium ion. This eventually produced the first photograph, in black and white, of a charged atom. With his long-time collaborator Robert Van Dyck, Dehmelt later was able to take a color photograph of a blue barium ion they named Astrid.

For his particle-trapping work, Dehmelt shared half of the 1989 Nobel Prize in physics with Wolfgang Pauli of the University of Bonn, who also devised anion trap. The work of Norman Foster Ramsey of Harvard University, the other 1989 Nobel physics laureate, led to the development of the atomic clock. The precise measurement methods made possible by the work of these three men madeit possible "to conduct experiments that might force us to reconsider some basic physical laws," according the Nobel Committee.

Late in his career, Dehmelt noted the discrepancies between the theoretical g-factor predicted by QED and the actual g-factor he had measured. Although the discrepancy was minuscule, Dehmelt speculated that it might indicate that the electron could be broken down into smaller and smaller particles, or subquarks, finally ending in the "cosmon." A linked cosmon and anticosmon, Dehmelt theorized, spontaneously came into being out of nothingness ina quantum jump and then instantly decayed, creating the Big Bang that beganthe universe.

Dehmelt became a naturalized U.S. citizen in 1962. He acted as a consultant to Varian Associates of Palo Alto, California, from 1956 through 1976, and hascontributed numerous articles to professional journals. He was elected to the National Academy of Sciences in 1978 and remains on its Physics and Astronomy Board. Dehmelt also won the 1995 National Medal of Science.

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