A Single Atomic Particle Forever Floating at Rest in Free Space: New Value for Electron Radius

An updated survey of mostly experimental spectroscopy work in Seattle on an individual closely-confined isolated atomic or elementary particle is presented. The classical notion of an atomic particle at rest in free space is discussed, and shown to be approximable by zero-point confinement of the particle in a laboratory trap. An important tool for cooling the particle, and in the case of an electron, for obtaining directly the difference of spin and cyclotron frequencies v_s, v_c, is side band excitation. The quantum numbers of the geonium "atom", an electron in a Penning trap, have been continuously monitored in a non-destructive way by the new "continuous" Stern-Gerlach effect. In this way the g-factors of electron and positron have been determined to unprecedented precision,

½g ≡ v_s/v_c ≡ 1.001 159 652 188(4),

providing the most severe tests of QED and of the CPT symmetry theorem, for charged elementary particles. From the close agreement of experimental and theoretical g-values a new, 10⁴ × smaller, value for the electron radius, R_g < 10^-20 cm, may be extracted. Other important results are: confinement of the individual positron, Priscilla, for 3 months, a tenfold suppression of the natural width of the cyclotron resonance, detection of an isomeric (cyclotron-excited) state via mass-spectroscopy, isolation and continuous detection of an individual proton, confinement of ≈ 100 antiprotons slowed to ≈ 3000 eV, confinement of a Ba⁺ ion to 13 ≈ 100 nm, and the demonstration of quantum jumps in geonium and in an isolated, individual regular atomic particle, Ba⁺. Some new experiments are proposed.