8th of February 2019 (Marseille) – PhD defense of Mathieu Collombon

Mathieu Collombon will defend his thesis on 8th of February 2019 at 11:00 am on the subject “Optimization of a force sensor based on ultracold atoms trapped in a vertical lattice”, realized at PIIM, under the direction of Martina Knoop.

The defense will take place in the “Thesis room”, on the St-Jérôme campus in Marseille.

You are also very welcome to the traditionnel buffet after the defense, that will take place at the service 322 (Lab’s cafeteria).


The work presented in this thesis describes the complete experimental set-up and approach to realize three-photon coherent population trapping in a cloud of radiofrequency confined Calcium ions. The realization of such a population trapping relies on a stringent conditions of the phase relationship between the three lasers involved in the interrogation process, and also their spectral linewidths. Our experimental approach is based on the optimization of the performance of a frequency-stabilized titanium-sapphire laser at 411 THz (729nm) at the 10−14 level, in term of relative frequency uncertainties. This laser’s frequency stability is subsequently transfered to a optical frequency comb by means of a phase-locked loop. Then the two other lasers involved (866 nm and 794 nm) are phase-locked to the optical frequency comb with the same technique. This work describes the transfer method along with its measured performances. With all the three lasers sharing the same ultra-stable frequency reference we have been able to experimentally observe for the first time a 3-photon dark resonance in the fluorescence spectra of the 40Ca+, signature of a coherent population trapping in a 3-photon scheme. The dependence of this resonance at experimental parameters, such as laser powers, laser detunings and local magnetic field, have been studied and are presented in this work. The preliminary results have allowed to explain the behaviour of the dark resonance and explored conditions for the use of the 3-photon dark line as a THz frequency standard.