The cyclotron and spin resonance of free electrons field confined in a small volume in ultrahigh vacuum have been observed via the rapid loss of electrons when their cyclotron motion is excited by the rf field and spin-dependent collision processes with polarized Na atoms in a beam, respectively. The electrons were polarized by spin exchange and then monitored through the spin dependence of the excitation process $e+\mathrm{Na}\mathrm{}\left(3S\right)\mathrm{}\to e+{\mathrm{Na}}^{*}\mathrm{}\left(3P\right)\mathrm{}$ and hence of their cooling rate.

• Received 3 June 1968

DOI:https://doi.org/10.1103/PhysRevLett.21.340