Last updated 29/09/2021

PhD and (master) internship proposal on the strontium experiment :

Quantum magnetism of ultracold fermions in optical lattices

We offer an experimental internship in the field of ultracold atoms. Our research theme is quantum magnetism, i.e., the collective behavior of ensembles of interacting spin-carrying particles.  Our experiment produces degenerate gases of fermionic strontium 87 atoms, that are then arranged on a periodic structure created by interfering laser beams: an optical lattice potential. Our system realizes the antiferromagnetic Heisenberg Hamiltonian.

Our aim is to study the conditions for the emergence of antiferromagnetic ordering. We can realize situations analogous to those encountered by electrons (of spin ˝) in crystalline materials, but also situations that strongly contrast with those, as a consequence of the spin 9/2 of our atomic species. These systems appear promising to create novel magnetic phases, such as spin liquids, with connections with topological materials and exotic forms of superfluidity. Presently, we are implementing protocols that exploit the narrow lines of strontium (of use e.g. to atomic clocks) to deterministically prepare low-energy spin textures and study their dynamics and correlations.

The work plan is as follows:

- The intern will be responsible for characterizing on the atoms a high-resolution imaging system (~1.2 µm), projecting onto a high-end, ultra-low-noise S-CMOS camera. The optical system has been built and characterized on an optical bench last year, and must now be moved on top of the vacuum cell. Figures of merit are optical resolution on the actual atomic cloud on the one hand, and detectivity on the other one – our expectation being close to single atom detectivity.

- Depending on progresses, the intern will participate in our protocols for preparing and evolving low-energy spin textures. The response of the sample to these manipulations, e.g. their degree of reversibility, will provide insight into the low-energy magnetic properties of the system. In the context of our collaboration with the team of T. Roscilde, ENS Lyon, we are developing observables for evidencing many-body entanglement.

The project is built in strong connection with a second experiment in our group (quantum magnetism with dipolar chromium atoms), and theory activities in our group (P. Pedri) and at ENS Lyon (T. Roscilde). The internship will provide an introduction to the essential experimental tools of cold atom experiments (lasers, optics, optomechanics, electronics), and will include a large part of team work on the ultracold atom setup.

This work may act as an introduction to a PhD thesis on the Sr experiment. As of October 2021, this project involves two PhD students (1st-year and 3rd year), and two permanent CNRS researchers.

        Project webpage and recent publications :

        Contact: Martin Robert de Saint Vincent, Bruno Laburthe-Tolra

PhD and Internship proposal on the Superradiant laser experiment

We offer an experimental internship in the field of atomic physics. Our proposal is in the context of a new experiment under development in our group, that aims at harvesting the phenomenon of superradiance to produce a new kind of coherent light source. Remarkably, the frequency stability and narrow linewidth of this light source, named “super-radiant laser”, makes it a candidate to serve as a new kind of optical clock, that relies on many-body entanglement between the emitters.

Our new experimental device will consist of an effusive beam of strontium atoms, in high vacuum. This atomic beam will first be slowed down by a laser beam; the atoms will then be excited into a metastable electronic state, before entering between two mirrors, within the mode of a high-finesse Fabry-Perot cavity. When the density of the atoms passing through the cavity is high enough, a cooperative effect known as super-radiance should occur, which increases the spontaneous emission rate and ensures that it will take place preferentially towards the fundamental mode of the Fabry-Perot cavity. Some original characteristics of this light source are an emission frequency mostly set by the atoms and thus robust with respect to perturbations of the system, and a linewidth that,
thanks to the quantum correlations between emitters, can be even below that of individual emitters.

The internship will be of a purely experimental nature. It will consist on the one hand in setting up the lasers that will allow to manipulate the strontium atoms, in order to create a monokinetic jet, colimated, and directed towards the Fabry-Perot cavity under vacuum. A first laser is an extended cavity laser operating at 461 nm. The laser will first be characterized. An acousto-optic optical setup will be used to create all the laser beams allowing: the transverse cooling of the atoms' motion; the longitudinal slowing down of the atoms; the deflection of the atoms thus slowed down by a well controlled angle, so that they propagate towards the Fabry-Perot cavity. A second laser will also be set up. It is an extended cavity laser, which operates at 689 nm. Here again, a complex optical system will be set up. The purpose of this system is to target the atoms using a highly divergent beam, in order to achieve the necessary population inversion to produce the desired laser effect.

Our team is composed of three professors, two CNRS researchers, three PhD students and one post-doc. We currently have two running experiments to study the collective properties of spinful ultracold gases, marked by quantum physics. We welcome (almost) every year one or more trainees on one of our experiments. Each time, we proposed an individualized work subject to the trainee, work that he/she could develop in autonomy while being put in connection with the rest of the team and its scientific projects.

Contact: Martin Robert de Saint Vincent, Bruno Laburthe-Tolra