Caroline Champenois

Frequency metrology based on trapped ions

Trapped cold ions as a basis for a frequency standard

Trapped ions have long be considered for frequency standard, first in the micro-wave domain, then in the optical domain. Our group works with calcium ions in the prospect of metrological applications and the expected performances for a single calcium ion optical clock were estimated here. Thanks to a three photon coherent population trapping in calcium-like ions, we were able to propose a THz frequency standard based on these ions. One of our original contribution to ion based frequency metrology is an optical clock based on an ion ring instead of a single ion (or a chain of ion). Laser cooled ions arrange in a ring when they are trapped in a linear multipole trap with steep enough axial confinement (about structural transition to a two ring structure) .

The mechanical equilibrium requirements and systematic shift calculations were led in our group in collaboration with Masatoshi Kajita, from NICT (Tokyo), guest professor of Université de Provence at the begining of this work.

Phase transfer between three visible lasers for coherent population trapping

Stringent conditions on the phase relation of multiple photons are a prerequisite for novel protocols of high-resolution coherent spectroscopy. In a recent experiment, we have implemented an interrogation process of a Calcium-ion cloud based on three-photon coherent population trapping, with the potential to serve as a frequency reference in the THz range . This high-resolution interrogation has been made possible by phase-locking both laser sources for cooling and repumping of the trapped ions to a clock laser at 729 nm by means of an optical frequency comb. The clock laser, a titanium-sapphire laser built in our lab reaches a linewidth of a few Hertz and a frequency stability below 10−14 at 1 s, performances which can be copied onto the two other sources.