Last updated 07/11/2024
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
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 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.
We have built a prototype for such a cold-atom-based superradiant laser. We want to tackle the unresolved issue of sustaining continuously a superradiant emission, thus harnessing its full potential as a clock. Our design is based on an effusive beam of strontium atoms inside a vacuum chamber, slowed, cooled, guided continuously up to an optical cavity, there to emit light in a superradiant fashion. The construction of the apparatus is completed, and we expect to acquire full control over the atomic velocity distribution in the next few months. The internship will thus be devoted to characterizing the signs of collective interaction between atoms and cavity (i.e., performing cavity-enhanced spectroscopy), and searching for superradiance signals in beat note spectroscopy. Throughout the PhD project, we will investigate the light properties to understand how the emitters synchronize their oscillations, and how the light coherence is related to correlations between all atomic emitters. Our experiment will have the unique capability to explore several distinct superradiant emission regimes, that will be identified through the spectral and correlation properties of the light and of the atoms. 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 new team member will develop his work in connection with the entire team, developing a general culture in atomic physics and many-body physics.
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
Superradiant laser team:
Benjamin Pasquiou, CNRS research engineer
Bruno Laburthe-Tolra, CNRS researcher
Martin Robert-de-Saint-Vincent, CNRS researcher
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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