Localized visible ${\mathrm{Ba}}^{+}$ mono-ion oscillator

An individual barium ion, continuously observed by laser fluorescence, has been isolated in a Paul rf quadrupole trap at room temperature. By optical sideband cooling its microscopically measured image has been reduced in thickness to ∼ 2 μm in the object plane, the diffraction limit. Estimated ion temperatures reached are $T_i\simeq 10 \mathrm{to} <36\mathrm{}$ mK. With cooling, the ion could be held indefinitely, without cooling ∼ 30 s. In the future the technique seems capable of attaining kinetic temperatures ∼ ${10}^{-8\mathrm{}}$ K, much lower than realized so far by other means, with corresponding far-reaching implications.