Rydberg atoms in HC-PCF

Highly excited Rydberg atoms display exceptionally large polarisability and are not only very sensitive to electric fields, but can also undergo long-range interactions with other Rydberg atoms. This makes them of great interest as sensitive electric field sensors or for optical nonlinearities down to the single photon level. We have introduced a thermal vapour of caesium into a hollow core kagomé-PCF and used light-induced atomic desorption (LIAD) to modulate the atom density over several orders of magnitude. After coupling an intense light beam into the fibre, atoms previously adsorbed onto the core walls are released and added to the vapour density. No cryogenic set-up (typically a magneto-optical trap) is required, raising the possibility of a fully fibre-based system. A broad-band guiding kagomé-style hollow-core PCF was used. After demonstrating the feasibility of the system we focused on understanding certain unexpected energy shifts in Rydberg states, which we attribute to surface charges on the core walls [Epple (2014)]. In parallel we have actively modulated the Rydberg states using an external electric field, permitting active switching of atoms in and out resonance by Stark shifting their energy levels, and sideband modulation [Veit (2016)].

(a) Excitation scheme and schematic of Rydberg excitation from a caesium vapour in HC-PCF. (b) Measuring Rydberg level Stark shifts spatially resolved by exploiting higher order optical modes to investigate surface effects (c) Active modulation of Rydberg resonances and side band modulation by applying a high frequency electric fields at the fibre position.