Figure 1
M. Steiner et al., Phys. Rev. Lett. (2013)

Trapped with a photon. A single ion (fluorescence image in blue square) is trapped by electric fields generated by ten electrodes (only two pointy ones shown) in an optical cavity formed by the ends of two optical fibers encased in metal sleeves (squarish items at right and left). The ion continuously absorbs and emits a single photon of a wavelength determined by the length of the cavity.