Last updated 26/10/2023

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

Dissipative preparation of quantum-correlated states of ultracold fermions

We offer an experimental internship in the field of ultracold atoms. Our experiment produces degenerate gases of fermionic strontium 87 atoms, arranged on a periodic structure created by interfering laser beams: an optical lattice. This setting leads to the production of strongly correlated fermions, a category of systems prone to the rich phenomena of quantum magnetism, exotic conduction regimes, and many-body entanglement. Primarily a condensed matter topic, this theme is now explored in new settings by the so-called quantum simulators, such as our experiment.

The search for quantum effects typically targets systems as decoupled as possible to the environment. However, a novel insight is that in specific cases, couplings to an environment can actually produce and stabilize quantum states with many-body correlations. This exciting new idea means that quantum phenomena may be harvested for quantum simulation or quantum sensing (clocks, atom interferometers) in a more robust manner than formerly thought.

Our system is suited to explore both sides of the problem: the Hamiltonian (conservative) production of entangled states, using original coherent spin preparation techniques, and the dissipative production of entangled states, by engineering losses that select specific inter-atomic correlations. We perform our experiments with strontium 87 atoms, fermions with 10 spin states in the electronic ground state, and narrow optical lines that enable us to engineer both the coherent manipulation of the spins and highly selective dissipation terms.

The intern will join our team during experiments in the Hamiltonian regime. By preparing deterministically the initial state of the atoms as a classical spin alternate ordering, we enable a subsequent dynamics under the influence of atom-atom interaction that should lead to low energy states of the Heisenberg antiferromagnetic interaction. We will characterize the preparation scheme, and measure the statistical properties of the collective spin to evidence the evolution of correlations. In parallel, the intern will have the responsibility of building a new laser system targeting the ultranarrow clock line of strontium, which will enable a whole new set of schemes to measure quantum correlations.

This internship is meant to act as introduction for a PhD project. The central objective of this PhD is to engineer a controlled dissipation producing and stabilizing a new set of quantum correlated states. We will target a narrow photoassociation line with a laser, to progressively extract from the sample pairs of atoms. As a consequence of the Pauli principle, photoassociated atoms will have to be in a spin-antisymmetric two-body state. The remaining atoms will be progressively pumped towards maximally spin-symmetric states, entangled, called Dicke states. We aim at demonstrating the robust production of these, and investigating their advantages for quantum sensors, i.e. clocks with measurement precision improved by the quantum correlations. Thanks to the use of an atom with a large spin F=9/2, exotic collective states will be at reach, beyond those usually drawn on a Bloch sphere.

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). We are in a close collaboration with the theoretical groups of T. Roscilde, ENS Lyon, on Hamiltonian dynamics, and of L. Mazza, LPTMS, on dissipative dynamics. The internship will provide an introduction to the essential experimental tools of cold atom experiments (lasers, optics, optomechanics, electronics), include a personalized project on the clock laser system, and a large part of team work on the ultracold atom setup.

Project webpage : https://gqm.lpl.univ-paris13.fr/AF/StrontiumProject.htm

Ultracold Strontium team:
Benjamin Pasquiou, CNRS research engineer    
Bruno Laburthe-Tolra, CNRS researcher           

Martin Robert-de-Saint-Vincent, CNRS researcher

Contact: martin.rdsv (at) univ-paris13.fr


PhD and (master) Internship proposal on the Superradiant laser experiment

Continuous superradiant laser with a laser-cooled atomic beam

Atomic clocks are vital components for many applications in our modern society, such as the operation of GPS and the synchronization of telecommunication networks. Clocks are also used as powerful tools to bolster investigations of fundamental physical phenomena, such as the detection of low-frequency gravitational waves.

Recently, a new type of clock has been proposed: the active clock using superradiant lasing. Instead of shining a very stable laser onto ultracold atoms to probe the atom resonance frequency (and thus measure time), the clock would operate by letting the atoms themselves emit light. Much like in a laser, cold atoms would be prepared in an excited state, then placed between two mirrors forming a cavity. The atoms then coherently emit light into the cavity mode. However, unlike a traditional laser, the light frequency will mostly be set by the atoms themselves, and not by the cavity. The light coherence will be set by a collective synchronization of the atomic dipoles with each other - a process called superradiance. Thus, in addition to its significance as a new clock architecture, this system is interesting from a fundamental point of view: it is an example of an open-dissipative system in which correlations of quantum nature may naturally arise. 

In the team Magnetic Quantum Gases (GQM) of the Laboratoire de Physique des Lasers, we have built a prototype for such a cold-atom-based superradiant laser. We want to focus on tackling the unresolved issue of sustaining continuously the emission in a superradiant laser, thus harnessing its full potential as a clock. This will be done using an effusive beam of strontium atoms inside a vacuum chamber, slowed, cooled, guided up to an optical cavity, there to emit light in a superradiant fashion. We will investigate the light properties to understand how the emitters synchronize their oscillations, and how the light coherence is related to many-body correlations between all atomic emitters.

The internship will be experimental research. The construction of the apparatus is nearing completion. The optical cavity is installed in the vacuum, and the laser system is functional. The Master student will be in charge of laser cooling and guiding atoms into the superradiant laser cavity, observing the first signs of collective interaction between the atoms and the light field in the cavity, and ultimately detecting superradiant emission. This implies implementing optical setups to shape and guide laser light onto the atoms, performing cavity-enhanced spectroscopy, and characterizing small superradiance signals in beat note spectroscopy. This work can then be continued into a PhD project, in which various superradiant emission regimes will be investigated, and the spectral and correlation properties of the light and of the atoms characterized. In collaboration with metrology experts, we will contribute to assessing the metrological interest (i.e., “performance” criteria to act as a clock) of atomic-beam continuous superradiant lasers.

Our group runs three experiments dedicated to the study of collective phenomena between atomic spins or dipoles. The two other experiments study quantum degenerate gases of interacting spinful atoms. The trainee will develop his work in connection with the entire team, developing a general culture in atomic physics and many-body physics.

Methods and techniques: Optics, electronics, atomic physics. The intern will deal with laser cooling, the principles of lasers and superradiant lasers, and spectroscopy methods.

References:
[1] H. Liu et. al., Rugged mHz-Linewidth Superradiant Laser Driven by a Hot Atomic Beam, Phys. Rev. Lett. 125, 253602 (2020).
https://arxiv.org/abs/2009.05717

[2] Laburthe-Tolra et al, Correlations and linewidth of the atomic beam continuous superradiant laser, SciPost Phys. Core 6, 015 (2023)

Project webpage : https://gqm.lpl.univ-paris13.fr/AF/SuperRadiantLaserProject.htm

Superradiant laser team:
Benjamin Pasquiou, CNRS research engineer
Bruno Laburthe-Tolra, CNRS researcher
Martin Robert-de-Saint-Vincent, CNRS researcher

Contact: benjamin.pasquiou (at) univ-paris13.fr


Post-Doctoral fellowship proposal on the Superradiant laser experiment


We advertise an opening for a 15 months postdoctoral position at the Laser Physics Laboratory (Université Sorbonne Paris Nord), aiming at realizing our first studies with a continuous super-radiant laser experiment.

Super-radiant lasers are a kind of “active optical clocks”, where emitters (atoms) with a narrow spectral line emit spontaneously in the mode of an optical cavity with comparatively broad spectral line. This produces a self-referenced light source, inherently robust to the effect of vibrations of the optical cavity – a key technological advantage compared to standard optical atomic clocks. Remarkably, the emission process itself, on a narrow line and thus from a somehow metastable state, is enforced by a collective effect stimulating intensive research: superradiance, i.e. spontaneous emission enhanced by inter-atomic correlations or synchronization. Thus, two research interests meet in the engineering of superradiant lasers: the demonstration and characterization of a new technology for frequency metrology, and the study of many-body physics in a dissipative quantum system.

Nowadays, a challenge is to reach the continuous superradiant regime. We have chosen a comparatively simple architecture, in which the use of a moderately narrow line of strontium (7.5 kHz) should enable superradiance from an effusive thermal beam, simply laser cooled and collimated before it crosses the mode of a high-finesse Fabry-Perot cavity. Today, the construction of the experimental apparatus is nearing completion. The post-doctoral researcher will be in charge of demonstrating the channelling of atoms from the oven into the Fabry-Perot cavity mode, and the laser excitation to reach population inversion. Then she/he will characterize the emission of light into the cavity, in order to demonstrate, for the first time, a continuous super-radiant laser. We should be in an ideal setting to verify whether the linewidth can reach below the natural linewidth of the atom, as a result of the synchronization of the atomic dipoles.

This work will be realized within the Magnetic Quantum Gases group at LPL, which, next to this project, operates two experiments on quantum magnetism with degenerate gases of chromium and strontium. It develops in collaboration with experimentalists at FEMTO-ST (M. Delehaye, clock-line continuous superradiant laser) and LCFIO (I.F. Barbut, free-space superradiance).

Project webpage : https://gqm.lpl.univ-paris13.fr/AF/SuperRadiantLaserProject.htm

Superradiant laser team:
Benjamin Pasquiou, CNRS research engineer
Bruno Laburthe-Tolra, CNRS researcher
Martin Robert-de-Saint-Vincent, CNRS researcher

Contact: martin.rdsv (at) univ-paris13.fr



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