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Annual Meeting Optical Society of America

Experiments with an isolated subatomic particle at rest

HANS G. DEHMELT

Published Jan 1, 1990• 4 citations
Publisher

Abstract

Research begun in the early seventies on geonium is reviewed. Geonium is a man-made atom, created at liquid helium temperature in ultrahigh vacuum from an individual electron in magnetic and electric trapping fields.
DOI
10.1364/oam.1990.wa3

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This article surveys experiments with individual closely confined atomic particles since their beginning in 1973. Such experiments have improved information on the size of an elementary particle on the same level as a quark, the electron, by at least three orders of magnitude. Their extension to the optical region promises atomic clocks of a reproducibility improved up to 100 000 times. The most important of the techniques developed for continuously detecting, cooling, and spin-state analyzing a permanently confined individual electron are described in some detail. The electron, trapped in ultrahigh vacuum at liquid helium temperature, is profitably viewed as a man-made atom, geonium.
Individual atomic and subatomic particles may be observed over long periods by confining them in “traps without material walls”. The Nobel Prize in physics was awarded in 1989 to Hans Dehmelt and Wolfgang Paul (together with Norman F. Ramsey) for first introducing this concept. Such traps are made possible by extending the principles of two‐dimensional focusing of particles to three dimensions. This led, in turn, to precision radiofrequency spectroscopy and quadrupole mass spectrometry. For example, side‐band cooling, in which electrons absorb photons with an energy just below the resonance energy and use their kinetic energy to supply the balance, allowed an electron to be held for ten months in the center of a magnetic trap. In this way, ½g was determined to be 1.001159652188(4).
A quasi-two-dimensional set of electrons (1 < N < 10(9)) in vacuum, trapped in one-dimensional hydrogenic levels above a micrometer-thick film of liquid helium, is proposed as an easily manipulated strongly interacting set of quantum bits. Individual electrons are laterally confined by micrometer-sized metal pads below the helium. Information is stored in the lowest hydrogenic levels. With electric fields, at temperatures of 10(-2) kelvin, changes in the wave function can be made in nanoseconds. Wave function coherence times are 0.1 millisecond. The wave function is read out with an inverted dc voltage, which releases excited electrons from the surface.