Geonium atom

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A geonium atom is a false "atom" created in a magnetic Penning trap.[1] A Penning trap is a combination of a homogeneous magnetic field and an electrostatic quadrupole potential. A single charged particle can be trapped indefinitely in a Penning trap. A small cloud of charged particles in such a trap is like a many-electron atom, with the difference that the role of the atomic nucleus is played by an adjustable external field in the trap.

In the simplest case, the system consists of only one electron or only one ion in the trap. Such quantum system is determined by the motion of one particle, like the hydrogen atom,[2] but the properties of the system are indeed very different. Its energy levels and g-factor of the charged particle can be measured and calculated with a very high precision.[3]

Hans Dehmelt of the University of Washington created the first Geonium atom in 1973, by quasi-permanently trapping an electron. In 1989 he and Wolfgang Paul of Bonn University received the Nobel Prize for Physics for their work on isolating individual electrons and ions and making exact measurements of them.[4]


  1. ^ Brown, L.S.; Gabrielse, G. (1986). "Geonium theory: Physics of a single electron or ion in a Penning trap". Reviews of Modern Physics 58: 233. Bibcode:1986RvMP...58..233B. doi:10.1103/RevModPhys.58.233. 
  2. ^ A hydrogen atom actually consists of two particles, the nucleus and the electron. But the motion of the atom as a whole is not relevant to its internal degrees of freedom. So, the motion of the electron relatively to the nucleus is equivalent to the motion of one particle, see center of mass frame.
  3. ^ Dehmelt, Hans (1988). "A Single Atomic Particle Forever Floating at Rest in Free Space: New Value for Electron Radius". Physica Scripta T22: 102–110. Bibcode:1988PhST...22..102D. doi:10.1088/0031-8949/1988/T22/016. 
  4. ^ "Geonium: A Fake but Useful Atom (Powerpoint Presentation)". Berkeley. Retrieved 2010-02-22.