QUANTIZED INFRARED-OPTICAL TRIPLE-RESONANCE ON A SINGLE COLD BARIUM ION

A single trapped and cooled Ba+ ion is irradiated by resonant visible light (493, 650 nm) alternating with light at 1.76 mu m which may excite the ion to its D-2(5/2) metastable state. The (absence of) visible resonance scattering probes the excitation, tuning spectra of which show vibrational sidebands that characterize the ion's temperature. Observed values as low as 120 mu K, one-eighth the Doppler limit, are ascribed to electronic Raman cooling by the visible light. Tuning spectra of the events of stimulated deexcitation indicate ion heating by the IR interaction. The results demonstrate the feasibility of vibrational spectrometry on a single particle that oscillates in a potential well, forming a quasi-molecule.