The End Cap Trap Fibre cavity is the latest development of traps that are designed to confine single atomic particles, in this case single calcium ions. One advantage of using single ions is that, as charged particles, they can be confined for long periods of time: up to several hours in some cases.
Lasers are used to cool the ion to what is known as the Doppler limit temperature, which for calcium ions is around 0.5 millikelvin. This ensures the ion’s motion is heavily reduced. A further advantage of using ions is that they are well localised and can be sited in a particular region of a standing wave field within a cavity. A single calcium ion, for example, should typically be confined to a space less than 50 nanometres in size, which is just a fraction of the wavelength of visible light.
The main objective of the experiment is to connect the single-ion miniature-cavity system to optical fibres, thereby enabling a single photon to be coupled efficiently to the outside environment or to another ion trap. By employing the ends of the optical fibres as cavity mirrors, the photons emitted by the ion are coupled directly into the fibre.
The single ions are held in the open structure on the right-hand-side of the picture below: The important parts being the vertically orientated cylindrical electrodes. 3-D electric trapping fields are generated by applying a radio-frequency signal at 15 MHz and 200 V peak-to-peak to the inner pins, whilst the outer cylindrical electrodes are grounded.