Axial, magnetron, cyclotron and spin-cyclotron-beat frequencies measured on single electron almost at rest in free space (geonium)

Abstract

THE monoelectron oscillator¹ consists of a ∼ 1-meV electron contained in a weak electric quadrupole field plus strong axial magnetic field (the Penning trap) on which the axial oscillation is continuously observable. It may profitably be looked on as an ultraheavy metastable pseudoatom, ‘geonium’ (through the trap and the magnet, the electron is bound to the Earth ultimately). The energy levels are given by² with v _c = eH/2πmc, 2v _c v _m − 2v _m² = v _z². We report here the measurement of the axial, magnetron, cyclotron, and spin-cyclotron-beat frequencies v _z , v _m , v _c − v _m and v _s −v _c +v _m using this apparatus, held at 4K. A new axial-frequency-shift technique using a 30-gauss deep magnetic bottle superimposed on the 18-kgauss field supplied by a superconducting magnet was used for the last two frequencies. The road to this advance was paved by two developments, namely the anharmonicity compensated trap³ yielding an axial line width of 10⁻⁷ and the “entropy reduction by motional sideband excitation” (ref. 4) method. The latter allows the centring of an electron liberated in the trap to close tolerance guaranteeing the constancy of v _z .