Abstract

Zero-point level confinement¹ in a trap is the quantum-mechanical equivalent of the classical single particle at rest in free space. Such confinement has been demonstrated—by the continuous Stern-Gerlach effect—only for the 150-GHz cyclotron motion in geonium, a single electron permanently confined in a cold Penning trap. Localizing the electron to ≈ 60 μm in the node of a standing wave in the trap cavity approximated free space, but decreased spontaneous emission tenfold. Driving the 60-MHz axial motion on a sideband higher by the ≈ 12-kHz magnetron frequency forced the magnetron motion to absorb the excess photon energy, shrinking its radius to ~ 15μm. Analogous laser cooling has reduced the oscillation amplitude of a Ba⁺ ion in a Paul rf trap to < 120 nm. As in nuclear magnetic resonance, confinement is now much smaller than the wavelength and sidebands disappear. Quantum jumps to and from an electronic metastable level of Ba⁺ have been demonstrated. Using In⁺ or a similar ion, this may make a monoion oscillator optical frequency standard with a 1000-day reproducibility of 10^-18 possible.

© 1986 Optical Society of America