Actualités & Séminaires

Title of seminar: Searching for PV in trapped molecular ions

Abstract :

Experimentally comparing left- and right-handed enantiomers is a powerful way to isolate parity-violating (PV) forces due to the unique asymmetry of chiral molecules. We are building trapped ion version of the search focusing on CHDBrI+ to detect PV arising from the nuclear weak force for the first time. Precision spectroscopy of such complex polyatomic molecular ions requires both cold generation and state-selective detection to be developed.
We aim to prepare cold CHDBrI+ through state-selective ionization in the VUV range. For detection we have connected a velocity map imaging detector to our ion trap. Through photofragment velocity measurements we will be able to assess the internal state populations.
We will discuss our progress on all these topics as well possible searches for BSM with chiral molecular ions.

References
[1]    A. Landau et al., J. Chem. Phys. 159, 114307 (2023)
[2]    Eduardus et al., Chem. Communi. 59, 14579 (2023)
[3]    I. Erez et al., Phys. Rev. X 13, 041025 (2023)

Title of seminar: High-Spatial-Resolution Dynamic Distributed Fiber-Optic Sensors: Instrumentation and Applications

Abstract :

For the past decade, Thales Research & Technology has been developing an architecture for high-spatial-resolution (＜10 cm) dynamic distributed fiber-optic sensors (＞kHz) based on a proprietary frequency-modulated laser source. I will present the general concepts of our interrogator, the associated instrumentation challenges—particularly the significance of laser source noise—as well as several applications for acoustic, mechanical, and hydrodynamic measurements.

Title of seminar: Gap plasmon antennas: light/material interaction in nano-cavities

Abstract :

We develop and study theoretically plasmonic nano-cavities where electrically or optically active materials are precisely positioned within the cavity for optoelectronic based applications and devices.  Plasmon gap resonances with metal nanocubes represent a fascinating and technologically significant phenomenon in the field of nanophotonics. Plasmons are collective oscillations of electrons in a metal, and when confined within nanoscale structures like cubes, they exhibit unique behaviors, particularly in the interparticle gaps.

First, we explore a new paradigm, coming from the microwave community, in which the light wave-like behavior is exploited to convert free-propagating electromagnetic waves at optical frequencies into direct current. We investigate optical rectennas composed of plasmonic nano-antennas associated with rectifying diodes to directly convert light into electricity. The main advantage of this technology comes from the ability to convert electromagnetic waves into electricity from far infrared to the visible range with potential high-power conversion efficiency (PCE). In our approach, we propose to study the interplay between nano-scale molecular electronics and plasmonics and the development of new functional nanostructured materials for energy harvesting. Our research efforts have resulted in the fabrication of nanopatch antennas able to couple resonant gap plasmon in nano-cavities integrating electrically active molecules and constructed with metallic nanocubes using a bottom-up approach. These nano-patch antennas are coupled with high-frequency molecular diodes to convert electromagnetic waves at optical frequencies. 

On a second approach, emitters placed within plasmonic nano-cavities that support intense optical confinement experience an environment that changes their coupling to light. In the weak-coupling regime light extraction is enhanced, but more profound effects emerge in strong coupling regime, where mixed light-matter states are generated. This new field of research in the LUMEN-PV team, concerns the study and development, through modeling and optical characterization, of patch nano-antennas integrating two-dimensional (2D) materials such as transition metal dichalcogenides (TMDs) in order to propose a valid design for LED fabrication.

Title of seminar: Dispositif électronique, développé au sein du LPL, de DDS multivoies pour la génération de signaux radiofréquence

Abstract :

Dans le cadre du PEPR quantique QUTISYM et à la demande des équipes d’atomes froids partenaires du projet, le service électronique électronique à développé un dispositif de génération de signaux radiofréquences de précision multicanaux.

Cette électronique est destinée à servir de source radiofréquence pour les expériences de physique quantique et de métrologique. Elle sera utilisée par différents laboratoires et partenaires du CNRS qui souhaitent disposer d’un système open source, reconfigurable et agile.

Je présente durant ce séminaire technique le projet réalisé, l’intérêt par rapport à des « solutions commerciales », et les perspectives d’évolutions du dispositif développé.

Title of seminar: Ultracold molecules beyond the bi-alkali paradigm: from quantum chemistry to new physics searches.

Abstract :

Despite tremendous progress in direct laser cooling of molecules, the only strategy so far able to deliver molecular gases at high phase-space density relies on the assembly from pre-cooled atoms in a two-step process: atom pairs are first converted into weakly bound molecules across a Feshbach resonance and later transferred to the absolute molecular ground state via stimulated Raman adiabatic passage. However, this method has so far been demonstrated only for bi-alkali systems with singlet electronic ground states.
In the first part of my talk, I will describe the association of alkali lithium and transition-metal chromium into LiCr dimers, which represent a prime candidate to realize quantum gases of paramagnetic polar molecules. The experimental investigation of several isotopic combinations of the Li-Cr, as well as the Cr-Cr systems, is used to benchmark state-of-the-art quantum chemistry methods. In the second part of my talk, I will present our recent proposal (with M. Tomza’s group, Warsaw), on next-generation searches for new physics based on high-spin, Σ-state, polar molecules in the ultracold regime, and I will explain how these can be realized by assembly of ultracold ytterbium and chromium atoms.

Title of seminar: Physics of frequency-shifting loops – Applications to sensors and signal processing

Abstract :

Frequency-shifting loops are a simple and efficient source of frequency combs. The spectral phase of these combs is quadratic and can be used to produce high repetition rate pulses through a temporal Talbot effect. Next, I will present some applications of these systems for spectroscopy and resonator characterisation. I will then show how the implementation of a double frequency-shift loop can be used to produce a dual-comb, thereby extending the applications of these architectures to coherent lidar and distributed acoustic sensors. Finally, I will present two applications of double frequency-shift loops for microwave photonics: real-time signal correlation and spectral analysis of broadband signals.

Title of seminar: Two-Body Contact Dynamics in a Bose Gas near a Fano-Feshbach Resonance

Abstract :

We investigate the real-time buildup of short-range correlations in a nondegenerate ultracold Bose gas near a narrow Fano-Feshbach resonance. Using rapid optical control, we quench the closed-channel molecular energy to resonance on sub-microsecond timescales and track the evolution of the two-body contact through photo-dissociation losses. Repeated pulse sequences enhance sensitivity to early-time two-body losses and reveal long-lived coherence between atom pairs and molecular states. The observed dynamics are accurately reproduced by our dynamical two-channel zero-range theory, which explicitly accounts for the resonance’s narrow width and finite closed-channel decay, establishing a predictive framework for correlation dynamics in quantum gases near Fano-Feshbach resonances.

Title of seminar: A Radio Astronomy-Based Spectrometer for Isotopologue Studies of Interstellar Molecules

Abstract :

Recent observations with ultra-sensitive radio telescopes, such as ALMA, have revealed that protostellar gas is rich in complex organic molecules (COMs). Many are thought to form on ices and then sublimate, but distinguishing ice-formed from gas-phase species remains a central question. Addressing this requires high-sensitivity observations supported by spectroscopic data that enable us to derive accurate isotopic ratios of individual molecular species in astronomical sources. However, such data are still lacking for rare isotopologues and highly excited states, posing a major limitation for interpreting astronomical observations.

To overcome this, we developed SUMIRE, an emission-type molecular spectrometer based on radio astronomy receiver technology. SUMIRE covers most of the main ALMA frequency ranges, Band 6 (211–275 GHz) and Band 7 (275–373 GHz), and allows simultaneous wide-band measurements up to 24 GHz. Its key innovation is a calibration system equivalent to that of radio astronomy, enabling direct comparison of laboratory and astronomical spectra. With purified isotopologue samples, SUMIRE also provides absolute intensity calibration values.

We are currently using SUMIRE to obtain spectra of deuterated and ¹³C-substituted methanol isotopologues, the most abundant saturated organic molecule in interstellar clouds, and applying them to astronomical data analysis. In this seminar, I will present these results, highlight the role of spectroscopy in astrochemistry, and also give an overview of the current situation of astrochemical research in Japan.

Vortices in liquid He, energy spectrum of quantum turbulence, quantum turbulence in atomic BECs

Following last week’s seminar, I will talk about quantum hydrodynamics and turbulence [1]. I will discuss important issues
by referring to both superfluid helium and atomic BECs.

• 1.Visualization of quantized vortices in superfluid 4He: A major recent development in the field of superfluid helium has been brought about by visualization experiments. The group led by Lathrop succeeded in visualizing quantized vortices using solid hydrogen particles [2], and subsequently in observing their reconnections. Minowa et al. employed silicon particles generated by laser ablation to achieve the direct excitation of Kelvin waves and to observe their three-dimensional helical structure [3]. Furthermore, through measurements of the chirality and propagation direction of Kelvin waves, they succeeded for the first time in identifying the orientation of vorticity in quantized vortices.

• Energy spectrum of quantum turbulence Turbulence is not merely a disordered arrangement of vortices; rather, the confirmation of statistical laws such as the Kolmogorov law provides crucial evidence. The energy spectrum of quantum turbulence (QT) within the Gross–Pitaevskii (GP) equation framework was first investigated by Brachet and collaborators. As in the case of atomic BECs, the GP equation
  describes a compressible fluid, and thus the energy spectrum must be decomposed into an incompressible component due to quantized vortices and a compressible component due to phonons. Starting from a Taylor–Green vortex, they studied decaying QT and demonstrated
  that the incompressible spectrum exhibits a −5/3 scaling during the decay process [4]. Subsequently, Kobayashi and Tsubota introduced large-scale forcing and small-scale dissipation into the GP equation to generate steady-state QT, and confirmed that the incompressible spectrum follows the −5/3 law in this regime [5].

• . Quantum turbulence in atomic BECs Because an atomic BEC is a finite system confined by a trapping potential, QT cannot be generated simply by driving flow as in superfluid 4He. Instead, several methods have been proposed to create QT, including manipulations of the trapping potential. Kobayashi and Tsubota demonstrated that biaxial rotation of a BEC can induce turbulence [6], and, building on this idea, Bagnato et al. succeeded in realizing and observing three-dimensional QT through controlled modifications of the trapping potential [7]. Two-dimensional QT has also been realized [8]. However, these remain finite trapped systems with only a limited number of vortices. For turbulence, the verification of statistical laws is desirable, but such observations were hampered by the nonuniform density of the trapped gas. Recently, however, Navon et al. created turbulence in a BEC confined by a box potential, succeeded in demonstrating a power-law density spectrum [9], and observed a cascade of excitations flowing from low to high wave numbers [10].

[1] M. Tsubota, K. Kasamatsu, Quantum Hydrodynamics and Turbulence (Oxford Univ. Press) (2025).
[2] G. P. Bewley et al. Nature 441, 588(2006).
[3] Y. Minowa, Y. Yasui, T. Nakagawa, S. Inui, MT, M. Ashida, Nat. Phys. 233, 21(2025).
[4] C. Nore, M. Abid, and M. E. Brachet, Phys. Rev. Lett. 78,3896 (1997); Phys. Fluids 9, 2644 (1997).
[5] M. Kobayashi, MT, Phys. Rev. Lett. 94, 065302(2005); J. Phys. Soc. Jpn. 74, 3248(2005).
[6] M. Kobayashi, MT, Phys. Rev. A76, 045603(2007).
[7] E. A. L. Henn et al. , Phys. Rev. Lett. 103, 045301 (2009).
[8] K. E. Wilson et al., Annu. Rev. Cold At. Mol. 1, 261 (2013) : W. J. Kwon et al., Phys. Rev. A 90, 063627 (2014).
[9] N. Navon, A. L. Gaunt, R. P. Smith, Z. Hadzibabic, Nature 539, 72 (2016)
[10] N. Navon, C. Eigen, J. Zhang, R. Lopes, A. L. Gaunt, K. Fujimoto, MT, R. P. Smith, Z. Hadzibabic, Science 366, 382 (2019)

Classical turbulence, quantum hydrodynamics, vortex lattices in rotating Bose-Einstein condensates (BECs)

Quantum hydrodynamics and turbulence [1] have long been studied in superfluid helium since the 1950s, as well as in atomic Bose-Einstein condensates (BECs) since 1995. In this two-part seminar series, I will present this topic in an accessible way.

1. Classical turbulence: Turbulence is an important problem in both fundamental science and engineering [2,3]. It is a strongly nonlinear and non-equilibrium phenomenon, and therefore very challenging. About 500 years ago, Da Vinci sketched Fig. 1, illustrating the Richardson cascade, in which large vortices break down into smaller ones. However, vortices in classical viscous fluids are unstable and not uniquely defined, so confirming this picture is not straightforward. Another important perspective on turbulence is its statistical laws. The most important statistical law of fully developed turbulence is Kolmogorov’s −5/3 law of the energy spectrum, which has been confirmed by many experiments and numerical simulations.

2. Quantum hydrodynamics: In parallel with such studies in fluid dynamics, research on the superfluidity of liquid helium has progressed in the field of low-temperature physics. This system is characterized by the Bose–Einstein condensation of 4He atoms. Many of its distinctive
   phenomena are explained by the two-fluid model, which describes the system as consisting of an inviscid superfluid and a viscous normal fluid, with their relative fractions determined by temperature. Moreover, vortices in the superfluid become quantized vortices with discrete circulation, which have become a defining hallmark of the quantum hydrodynamics of this system.
   Turbulence generated by such quantized vortices is referred to as quantum turbulence. The typical platforms for quantum hydrodynamics are superfluid helium and atomic BECs. In the strongly correlated Bose system of superfluid ⁴He, the vortex filament model is employed. In contrast, for atomic BECs, the Gross–Pitaevskii (GP) equation provides a quantitatively accurate description.

3. Formation of a lattice of quantized vortices in rotating BECs One of the central problems in quantum hydrodynamics is the formation of a quantized vortex lattice in a rotating BEC. In the case of a classical viscous fluid, when the container is rotated, the fluid undergoes rigid-body rotation with the same rotation frequency as the container. However, due to the quantization of circulation, a quantum fluid does not behave in this way. Instead, a number of quantized vortices proportional to the rotation frequency penetrate into the condensate, forming a triangular lattice, thereby realizing rigid-body rotation of the superfluid. This phenomenon had already been known in superfluid helium, but the dynamics leading to it were observed by the experimental group at ENS [4]. A BEC confined in a harmonic trapping potential first
   undergoes quadrupole oscillations, after which its surface becomes unstable, allowing quantized vortices to enter. Ultimately, a triangular lattice is formed. Such behavior has been confirmed by numerical simulations of the GP equation [5].

[1] M. Tsubota, K. Kasamatsu, Quantum Hydrodynamics and Turbulence (Oxford Univ. Press) 2025.
[2] U. Frisch, Turbulence: The Legacy of A. N. Kolmogorov (Cambridge University Press) 1995.
[3] P. A. Davidson, Turbulence: An Introduction for Scientists and Engineers (Oxford University Press) 2015.
[4] K. W. Madison et al., Phys. Rev. Lett. 86, 4443 (2001).
[5] MT, K. Kasamatsu, M. Ueda, Phys. Rev. A65, 23603(2002): K. Kasamatsu, MT, M. Ueda, Phys. Rev. A67,33610(2003)

Title of seminar: Quantum Fluctuation Forces Near Material Interfaces

Abstract:

Fluctuations are ubiquitous in classical and quantum physics, affecting various disciplines like biophysics, gravity, chemistry, and cosmology. In recent years, the pursuit of miniaturization has led to a surge in interest in electromagnetic quantum fluctuation-induced interactions, both for fundamental and technological reasons. Despite often being imperceptible at the macroscopic scale, these interactions can indeed be rather significant in microscopic systems, presenting challenges as well as opportunities for quantum technologies. Paradigmatic examples include van der Waals and Casimir forces, which can be beneficial or disruptive in device design. Recent advancements have enabled exploration of nonequilibrium physics, quantum electrodynamics, atomic, and condensed matter physics as well as their interfacing within this research domain. Understanding these forces provides novel perspectives on the underlying physics and paves the way for future developments.

Title of seminar: Towards the First Measurement of Parity Violation in Chiral Molecules – New Attempts and Future Prospective

Abstract:

A fundamental discovery of this century is that our Universe is “left” handed (Weinberg-Salam-Glashow theory), the electro-weak interaction (parity-odd) gives rise to primarily left-spinning electrons during beta decay. In 1957 Lee and Yang discovered parity violation (PV) in the K+ decay, which was confirmed shortly after by Wu et al. for the b-decay. In the last decade PV effects in atomic transitions have been measured and calculated to high accuracy confirming the so-called standard model in particle physics. PV through Z-boson exchange between electrons and nucleons, leads to a small energy difference between enantiomers of chiral molecules although there is no experimental verification yet
of this distinct symmetry breaking effect despite many attempts. Current high resolution optical spectroscopy carried out in the CO2 laser frequency range (878-1108 cm-1) at LPL in Paris achieves resolutions of about 1 Hz. Recent calculations in our group applying the standard model show that PV effects in vibrational transitions of chiral methane derivatives CFXYZ (X,Y,Z= H, Cl, Br, I) are in the mHz range and below the detection limit. Our research group is therefore searching for molecules including heavy elements (because of the PV Z5-scaling) to achieve enhanced PV effects in the Hz range. New promising candidates are presented in collaboration with the French PV initiative, which aims at a 100 mHz resolution in Ramsay-Fringes experiments using quantum cascade lasers. Another future alternative is single-molecule spectroscopy in traps at ultra-cold temperatures.

Title of seminar: From Meyer and Mendeleev to Oganessian and Dirac: What next after the superheavies and is there an end in sight for the Periodic Table?

Abstract:

The first periodic table of elements was proposed by Dmitri Ivanovich Mendeleev in 1869. It was based on arranging the elements in ascending order of atomic weights and grouping for similarities in chemical properties. Mendeleev predicted the existence and properties of new elements and pointed to accepted atomic weights that were flawed. At this time, it was not known how far one can increase the atomic weight to the critical point where heavy elements become unstable and undergo radioactive decay or when electronic levels dive into the Dirac sea. A century later it was speculated that the periodic table would end with heavy atomic nuclei containing no more than 100 protons because of the immense Coulomb repulsion between the protons. In 1948, however, Goeppert-Mayer pointed out that the nuclear shell model can significantly increase the stability of the atomic nuclei, and Meldner demonstrated in 1967 that the next proton-neutron-shell closure (island of nuclear stability) will take place
at a nuclear charge of Z = 114 and a neutron number of N = 184. Over the past two decades, we gained detailed insight into the nuclear stability problem by producing new superheavy elements up to a nuclear charge of Z = 118 (oganesson). The periodic table is most fundamental to chemistry, but key questions remain unanswered: where does the periodic table end from a theoretical and practical point of view? Can we still do chemistry with exotic and highly unstable elements? How can one predict the chemical and physical behaviour of these superheavy elements as the electronic spectrum becomes dense? What is quantum theory doing in the super-critical Coulomb field region when electronic states dive? Do
superheavy elements exist in nature, and are these produced in supernova explosions or neutron star mergers?

Title of seminar: Observation of entanglement in a cold atom analog of cosmological preheating

Abstract:

Parametric resonance is a universal phenomenon that arises across all scales, from Faraday waves in a water container to particle creation in the early Universe. (Quasi)particles are created in pairs of opposite momenta, and their exponential growth is triggered by fluctuations, such as thermal noise. However, if the initial mean number of (quasi)-particles is zero, vacuum fluctuations initiate the growth, yielding an entangled state. In this seminar, I will report on the experimental parametric creation of opposite-momentum quasi-particles in a Bose-Einstein condensate, and on the evolution of their number and entanglement. This experimental observation is made possible by the introduction of a novel entanglement criterion, to relate number correlation function to entanglement.

There should furthermore be, tomorrow thursday, the next presentation in the series by Peter Schwerdtfeger. Let’s enjoy our summer science camp and come in force to both!

Title of seminar: Left or Right in Nature – The Origin of Biomolecular Homochirality

Abstract:

Emil Fischer’s studies of peptides and sugars led to chiral molecules (D-sugars and L-amino acids) and to the confirmation of Pasteur’s conjecture that the universe is disymmetric. It is well known that D-sugars and L-aminoacids completely dominate the biochemistry of living organisms. But what is the cause for this single handedness in nature? Is biomolecular homochirality a necessary condition for life? Biomolecular homochirality at the microscopic level is supposed to be responsible for most of the symmetry breaking effects at the macroscopic level, for example that our heart is on the left-hand side of our body. On the microscopic side, a fundamental discovery of the last century is that our Universe is intrinsically left-handed (Weinberg-Salam-Glashow theory), the electro-weak interaction (parity-odd) gives rise to primarily left-spinning electrons during beta decay. In 1957 Lee and Yang discovered parity violation in the K+ decay, which was confirmed shortly after by Wu et al. for the -decay. It is now well accepted that parity violation can lead to a small energy
difference between enantiomers of chiral molecules, although there is no experimental verification yet of this distinct symmetry breaking effect. Can this tiny effect be responsible for biomolecular homochirality in nature?

Title of seminar: Quantum Probes of Fundamental Physics with Ultracold Molecules

Abstract:

Some of the biggest mysteries in physics—such as why the universe is made mostly of matter—suggest that our current understanding, the Standard Model of particle physics, is incomplete. One way to explore these open questions is by searching for a very slight distortion in the shape of the electron. If the electron is not perfectly round, it would point to new laws of physics that lie beyond our existing theories.

To look for this tiny effect, we use ultracold molecules as quantum sensors. By cooling molecules to temperatures near absolute zero and trapping them with beams of light, we can observe their quantum behaviour with exceptional precision. These tabletop experiments allow us to explore fundamental physics at energy scales that rival those probed by the world’s largest particle accelerators.

Beyond their role in fundamental physics, ultracold molecules also offer a rich platform for quantum technologies. Their complex internal structure makes them useful for quantum computing, highly sensitive measurements, and even studying chemical reactions in entirely new quantum regimes. Together, these capabilities make ultracold molecules a powerful toolset for advancing both our understanding of nature and the technologies of the future.

Title of seminar: How to create a distributed entangled sensor network with tunable long-range interaction using a double-well superlattice?

Abstract:

In this work, we consider a system made of several double wells (DW) loaded with atoms that interact via dipolar interactions (as described in [1] for example). Performing a two-mode approximation for each DW, we can derive an effective spin-Hamiltonian that describes the interactions between the DWs and that can be tuned by playing on the geometry of the DW superlattice or adding light induced dipolar interactions [2]. This Hamiltonian leads to entanglement and squeezing between the DWs when we perform a quench experiment. We are able to determine numerically and analytically the amount of local and shared squeezing using multiparameter squeezing [3] for different sets of Hamiltonian parameters, and we estimate the metrological interest of our system. Finally, we propose two protocols to take advantage of this entangled sensor network in the case of only two DWs, one for enhanced gradiometry using ellipse fitting methods [4, 5], and the second one using quantum non demolition measurements to transfer the multiparameter squeezing delocalised on the whole system to a single DW [6].

References:
[1] L. Masi, T. Petrucciani, G. Ferioli, G. Semeghini, G. Modugno, M. Inguscio, and M. Fattori, Phys. Rev. Let. 127 020601 (2021)
[2] M. Maiwöger, M. Sonnleitner, T. Zhang, I. Mazets, M. Mallweger, D. Rätzel, F. Borselli, S. Erne, J. Schmiedmayer and P. Haslinger, Phys. Rev. X 12 031018 (2022)
[3] M. Gessner, A. Smerzi, and L. Pezzè, Nat. Com. 11 3817 (2020)
[4] R. Corgier, M. Malitesta, L. A. Sidorenkov, F. Pereira Dos Santos, G. Rosi, G. M. Tino, A. Smerzi, L. Salvi, and L. Pezzè, arxiv.2501.18256 (2025)
[5] T. Petrucciani, A. Santoni, C. Mazzinghi, D. Trypogeorgos, F. S. Cataliotti, M. Inguscio, G. Modugno, A. Smerzi, L. Pezzè, and M. Fattori, arXiv:2504.17391v1 (2025)
[6] L. Pezzè, A. Smerzi, M. K. Oberthaler, R. Schmied, and P. Treutlein, Rev. of Mod. Phys. 90 (2018)

Title of seminar: Floquet-Engineering of Feshbach Resonances and Bound States in the Continuum

Abstract:

His talk will be on the control of interaction properties, in ultracold atom systems, and how it enables the realization of unconventional bound states (also seen in different fields such as photonics ans acoustics)

Title of seminar: Progress in clock comparisons and networks at NIST, Boulder.

Abstract:

Atomic clock comparisons represent a means to characterize the consistency of optical atomic clocks as frequency references for future redefinition of the SI second and for tests of fundamental physics. In this talk I will discuss schemes aimed at improving measurement precision in clock comparisons, including recent work at also using time and frequency techniques for the realization of quantum networking.

Title of seminar: Wave turbulence in Bose-Einstein condensates

Abstract:

Wave turbulence refers to a state of a continuous medium that is populated by random, mutually interacting waves spanning a broad range of scales. When these waves are only weakly nonlinear, we can turn to WT theory, a powerful mathematical framework that statistically characterizes such turbulent wave fields.

In this talk, I will focus on how WT theory has been applied and further developed to describe density waves in Bose-Einstein condensates, covering both 4-wave and 3-wave interaction regimes. This allows us to derive universal scaling solutions, including steady-state spectra known as the Kolmogorov–Zakharov (KZ) spectra and self-similar evolutions. All these theoretical predictions have been tested and confirmed by direct numerical simulations of the nonlinear Schrödinger equation (the mean-field description of a BEC) as well as by simulations of the ascociated wave-kinetic equations derived by WT thoery.

I will also discuss the current state of experiments relevant to turbulent BECs. In particular, I will share insights from our latest results on the “equation of state” for steady turbulent cascades in Bose-Einstein condensates—recently reported in [Dora et al. Nature 620, 521 (2023)].

Title of seminar: Metrology with hot atomic vapors

Abstract:

Despite being more than 50 years old, the field of metrology with hot atomic vapors is still receiving a lot of attention. Vapor cells remain pivotal in numerous fundamental precision physics experiments. Over the past 15 years, the advent of miniaturized cells and lasers have enabled the development of quantum sensors boasting excep;onal precision and minimal power consumption. This innovation has led to a myriad of practical applications. The rapid progress in laser technologies, integrated photonics, and material science has further enhanced these sensors while also paving the way for new technologies essential to quantum optics. The experimental simplicity, robustness, and fundamental properties of hot atomic systems hold significant promise for realizing real-world quantum devices. In this seminar, I will present my contributions to this expansive field. These include the spectroscopy of hot vapors at the nanoscale, the development of optically pumped magnetometers and their
applications to the detection of dark matter and rotation sensing, as well as the development of miniaturized optical clocks. The presentation will culminate in a discussion on the emerging applications of hot vapors in the realm of quantum optics.

Title of seminar: Shear flow and vortex array instabilities in annular strongly-correlated atomic superfluids

Title of seminar: Onset of continuous cavity-mediated collective phenomena in an atomic beam

Abstract:

An atom-cavity system is a simple yet rich open quantum system.

By adjusting the characteristic rate of each individual component, the nature of the interplay can be manipulated. Here, we present the case where the dissipation rate of a single mode of an optical cavity is larger than the decay rate of the gain medium. In this scenario, photons do not remain in the cavity mode for long, so the cavity field is primarily determined by the photons emitted and absorbed by the atomic gain medium. Contributions to the atomic decay rate include spontaneous decay into vacuum modes as well as inhomogeneous and homogeneous broadenings. This regime is often referred to as the ‘bad-cavity regime.

We demonstrate, theoretically and experimentally, that a large ensemble of atoms can drive this coupled system into the ‘strong-coupling regime’, characterized by a non-linear response to an external drive. We argue that ­­this regime arises not from strong single atom-cavity coupling, but from the collective weak coupling of many atoms to a single cavity mode. For an inverted sample, we will show that this regime results in optical amplification of the external drive.

The experimental system consists of a beam of Sr atoms. The beam has a large vertical velocity, resulting in a short transit time for atoms passing through the cavity mode, while being cooled in the other two directions. The velocity along the cavity axis is particularly important as it determines the atom-cavity interaction phase. We show how to prepare an ensemble of either ground or excited state atoms that exhibit collective effects.

Title of seminar: Probing supersolidity through excitations in a spin-orbit-coupled Bose-Einstein condensate

Abstract:

Spin-orbit-coupled Bose-Einstein condensates are a flexible experimental platform to engineer synthetic quantum many-body systems. In particular, they host the so-called stripe phase, an instance of a supersolid state of matter. The peculiar excitation spectrum of the stripe phase, a definite footprint of its supersolidity, has so far remained out of experimental reach. We achieve in situ imaging of the stripes and directly observe both superfluid and crystal excitations. We investigate superfluid hydrodynamics and reveal a stripe compression mode, thus demonstrating that the system possesses a compressible crystalline structure. Through the frequency softening of this mode, we locate the supersolid transition point. Our results establish spin-orbit-coupled supersolids as a platform of choice to investigate supersolidity and its rich dynamics.

Title of seminar: Quantum jumps in a single atom: application in photon counting and role in open quantum systems

Abstract:

The notion of quantum jumps was first introduced by Niels Bohr in 1913 to describe the abrupt change of state of electrons in atoms. They were experimentally observed for the first time in trapped ions in 1986 using the concept of electron shelving which was used to precisely measure the lifetime of metastable states in ions. In this talk, I will first describe a photon counting technique based on quantum jump detection in a single Rubidium atom which heralds a photon absorption [Phys. Rev. Research 6, 033338 (2024)]. Such a technique is interesting for a growing number of applications that require high sensitivity and strong background rejection through frequency discrimination, for example free space quantum communication in daylight or space classical communications. The quantum efficiency, dark counts and background rejection of this single-atom photodetector were characterized using single-photon level laser photons. With this technique, I will also report on the detection of spontaneous parametric down conversion photons, which enable studies of atom-light interaction at the single quanta level. Finally, I will present a proposal to experimentally distinguish different unravelings of the so-called Lindblad master equation appealing to stochastic conditional dynamics via quantum trajectories [Phys. Rev. Research 6, L032057 (2024)]. Each unraveling of the master equation is known to be linked to a photodetection scheme. We show that it can be unraveled using nonlinear quantum trajectories that correspond to different types of quantum jumps. We focus on the simple case of resonance fluorescence of a single atom in two popular photodetection schemes: the Poisson-type, corresponding to direct detection of the photons scattered from the two-level emitter, and the Wiener-type, revealing complementary attributes of the scattered field such as the wave amplitude and the spectrum.

Quantum Turbulence across Dimensions

Quantum turbulence (QT) is a disordered state of quantized vortices in superfluids and atomic Bose–Einstein condensates (BECs), offering a minimal and well-defined model of turbulence [1]. Its properties strongly depend on dimensionality.

1. Turbulence: 2D vs 3D
In three-dimensional (3D) classical and quantum turbulence, vortex stretching plays a central role, enabling a direct energy cascade from large to small scales (Richardson cascade), where energy is dissipated at short wavelengths. In contrast, two-dimensional (2D) turbulence lacks vortex stretching. Instead, both energy and enstrophy are conserved in the inviscid limit, leading to a dual-cascade scenario: an inverse energy cascade toward large scales and a direct enstrophy cascade toward small scales, as described by Kraichnan and Batchelor. The inverse cascade promotes the formation of large-scale coherent vortical structures, closely related to Onsager’s statistical theory of point vortices and negative-temperature states.

2. 2D Quantum Turbulence
In atomic BECs described by the Gross–Pitaevskii (GP) model, realizing ideal 2D turbulence is challenging. Vortex–antivortex pair annihilation breaks strict enstrophy conservation, compressibility introduces sound emission, and finite system size limits the inertial range. As a result, numerical and experimental studies often observe dominant direct cascades rather than clear inverse cascades. Nevertheless, under suitable conditions, vortex clustering and signatures of Onsager-like states have been reported, highlighting the interplay between vortex dynamics, dissipation, and finite-size effects in 2D QT.

3. Crossover across Dimensions
To clarify how QT changes across dimensions, we control the confinement height R₂ in a cylindrical box potential within the GP framework. For small R₂, the system shows 2D-like behavior: vortex–antivortex annihilation dominates and clustering consistent with inverse transfer develops. For large R₂, Kelvin waves can be excited along vortex lines, inducing reconnections, phonon emission, and a direct energy cascade characteristic of 3D Vinen turbulence. The results demonstrate that the excitation of Kelvin waves, determined by the system height, governs the transition from 2D to 3D QT.

References:

[1] M. Tsubota and K. Kasamatsu, Quantum Hydrodynamics and Turbulence, Oxford University Press (2025).
[2] L. Onsager, Nuovo Cimento Suppl. 6, 279 (1949).
[3] R. H. Kraichnan, Phys. Fluids 10, 1417 (1967).
[4] G. K. Batchelor, Phys. Fluids Suppl. 12, II-233 (1969).
[5] W.-C. Yang, X. Wang, and M. Tsubota, arXiv:2502.06133 (2025).

Title of seminar:  (Cold) Molecules as a tool to probe fundamental physics

Abstract:

Modern physics is struck with a paradox: there are very good reasons to believe that our current understanding of Nature is incomplete, yet it is exceedingly difficult to conduct an experiment which contradicts our best theories. This tension is particularly palpable since the Large Hadron Collider explored a wide range of energies without a clear detection of new physics, thereby discarding many extensions Beyond the Standard Model (BSM). Searching for new physics in the high energy domain now demands extremely large investments to build bigger and brighter instruments. Another approach, complementary but very powerful, is to perform small scale, low-energy experiments but with very high precision¹. In the last 20 years in particular, this led the community to look for new physics in much larger objects than elementary particle: molecules. Many proposals and experiments have demonstrated the potential of molecules to test our fundamental understanding of Nature: from probing variations of fundamental constants like the electron mass over the proton mass  or the fine-structure constant , or different models for dark matter, to testing the symmetrisation postulate of Quantum Mechanics or Bose-Einstein statistics. Especially notable are experiments currently responsible for the most stringent limit on the value of the electron electric dipole moment (which constraints strongly potential BSM theories).

However, the field is still in its infancy: the molecules that are currently used to explore new physics are composed of 2, 3 or 4 atoms at most, even though larger molecules offer qualitatively distinct opportunities in fundamental physics. The abundance of nearly degenerate rovibrational levels in the larger, polyatomic molecules (with more than 10 atoms) enhances their sensitivity to variations of fundamental constants or to potential ultralight bosonic dark matter. They can also provide a new system for implementing quantum computing, using either rotational or vibrational levels, and taking advantage of robust systematic error rejection schemes. Having more than 3 atoms also opens up the possibility to use molecular chirality to probe parity-violating interactions. Indeed, the energy levels of two enantiomers (the mirror-images of chiral molecules) are predicted to be slightly different, because of the parity-violation inherent to the weak interaction, or as a result of their interaction with dark-matter fields. Thus, a measurement of this symmetry-breaking energy difference ΔE_PV is a sensitive probe of the Standard Model and of physics BSM.

However, as the number of atoms in a molecule goes up, the number of energy levels increases very rapidly, as well as the couplings between these energy levels. These couplings limit the applicability of the usual cooling mechanisms because they induce population losses towards many different states. Couplings between different vibrational modes (denoted in the literature as Intramolecular Vibrational Redistribution (IVR)) also blur out spectroscopic resolution by what can be viewed as a loss of coherence due to non-radiative dynamic energy distribution in the molecule.

In this talk I will review the current use, the potential ahead and the obstacles on the way of using molecules for tests of fundamental physics, focussing on our on-going attempt to measure ΔE_PV in chiral molecules at the Laboratoire de Physique des Lasers.

Title of seminar:  Stages of the relaxation for a far-from-equilibrium trapped superfluid

Abstract:

Understanding the initial conditions that drive many-body quantum systems out of equilibrium is essential for getting into their thermalization dynamics. In this work [1,2,3], we identify two excitation regimes that lead a trapped Bose–Einstein condensate into turbulence regime evolving resulting in distinct final states. In the subcritical regime, the condensate partially reemerges after turbulence, whereas in the supercritical regime it dissolves completely into a thermal state. Despite these differences, both cases exhibit relaxation stages with common features: a direct energy cascade, the emergence of a nonthermal fixed point (characterized by identical scaling exponents), a prethermalization plateau, and eventual thermalization. Our results show that turbulence relaxation develops independently of the system’s initial conditions or its ultimate state. At late times, both regimes display universal scaling dynamics consistent with predictions from wave turbulence theory. Finally, by analyzing the time evolution of the condensate’s momentum distribution center of mass, we demonstrate how kinetic-energy dominance reflects the thermalized nature of the final states in each regime. The present results advance the field by showing that thermalization in far-from-equilibrium quantum systems follows universal relaxation dynamics, even when the final states differ, thereby deepening our understanding of the time evolution of many-body quantum systems. We shall present a new possible interpretation for pre-thermalization as well as an analysis of the construction of the coherent length during the last stage of thermalization of the system.

1. M. A. Moreno-Armijos et al – Phys. Rev. Lett. 134. 023401 (2025)
2. L. Madeira et al – Proc. Nat, Acad. Sci. -PNAS 121, 24044828121 (2024)
3. A. D. García-Orozco et al – Phys. Rev. A 106, 023314(2022)

Title of seminar: Generalised hydrodynamics for integrable and quasi-integrable gases

Abstract:

I will review the theory of generalised hydrodynamics (GHD) for integrable quantum gases, with a particular emphasis on the impact of integrability-breaking perturbations and the emergence of long-range correlations during the dynamics even when integrability is broken.

Title of seminar: An optical lattice clock with a bosonic isotope of mercury

Abstract:

Among other neutral species, mercury has interesting properties for an optical lattice clock such as a low sensitivity to blackbody radiation (16 times lower than Yb, 30 times lower than Sr) and a
high vapour pressure at room temperature. So far, the 199Hg fermionic isotope was the only isotope used in a mercury clock, but its limited lifetime in the excited state will prevent to fully exploit the
new generation of ultrastable lasers to come. Using bosonic isotopes instead is a way to bypass this limit thanks to a potentially unlimited lifetime.

We report the first observation of the ¹⁹⁸Hg bosonic transition in an optical lattice clock, which results from several key experimental developments and a challenging search of a narrow transition in a wide uncertainty span.

The bosonic clock transition is forbidden and needs to be induced thanks to a high magnetic field. This is the so called quenching method¹. It allows longer probing times, adjustable to the laser properties. Hence, a first key step was developing a setup to produce a large enough magnetic field to induce the bosonic transition with the highest coupling achievable. Another challenge was implementing a widely tunable and flexible probe laser while maintaining the ultra-low noise properties, in order to probe any of the mercury isotopes with no additional noise. The coupling is also increasing with the probe power, so a major step was to significantly increase our deep UV ultrastable light power.

Given all these experimental advances, we calculated that we still had a relatively weak coupling and hence a narrow line transition to be found in a large frequency span. We performed various measurements and checks thanks to the ¹⁹⁹Hg isotope, especially a substantial alignment work, to optimize our chances to find the transition. Thanks to cumulated efforts, the search of the 198Hg transition was a success, making it the first observation of a mercury bosonic isotope transition.

We further obtained an operational optical lattice clock with the bosonic ¹⁹⁸Hg, already reaching a stability of 10-15 at 1 second. We have undertaken several studies of this new transition, in particular we measured the quadratic Zeeman shift coefficient with an uncertainty suitable to control this shift to 10^-17 or better. We also started studying other systematic effects such as the probe light shift and measuring the magic wavelength. Finally, we are working towards measuring, for the first time, the ¹⁹⁸Hg/⁸⁷Sr optical frequency ratio.

• ¹ A. V. Taichenachev et al., “Magnetic Field-Induced Spectroscopy of Forbidden Optical Transitions with Application
  to Lattice-Based Optical Atomic Clocks”, Phys. Rev. Lett., vol. 96(8), p.083001, 2006.

Title of seminar: Mid- and Long-Wave Infrared Optoelectronics for Free-Space Optical Communications

Abstract:

Free-space optics offer an attractive alternative for broadband data transmission when fiber optics are neither practical nor feasible. This technology has emerged as a strong candidate with a wide range of potential applications from everyday broadband internet to satellite links. Today, the availability of high-quality transmitters and detectors operating in the near-infrared window makes the 1.55-micron optical wavelength the natural choice for free-space optical systems. However, the atmospheric transmission spectrum has two other transparency windows that can be considered namely one between 3 and 5 microns and the other between 8 and 11 microns. In this context, midinfrared quantum cascade devices have become prime candidates for data transmission applications, especially in fog or haze, where they significantly outperform near-infrared and visible light sources. In addition, atmospheric turbulence in the propagation path severely degrades the optical signal by causing beam spreading and wandering, scintillation or loss of spatial coherence. In this seminar, I will review our recent results on free-space optical communications, which have shown that quantum cascade lasers can be used as unpredictable light sources for data security, using complex photonic chaos for message encryption and synchronized chaos for message transmission. Between 8 and 11 microns, this technology is even more interesting because the random thermal background radiation of the blackbody further complicates the task of deciphering a potential spy, meaning that communication is even more secure. My presentation will also cover our recent advances in multi-gigabit-per-second room temperature data transfer based on midinfrared quantum optoelectronics. While these results can profoundly revolutionize the future of free-space laser communications, the goal, however, will be to implement this new optoelectronic technology in an actual outdoor testbed, especially to prove the superiority of the mid and long wave infrared domains.

Title of seminar: Fast compression of a Bose-Einstein condensate and the new experiment for 2D Bose gases

Abstract:

In this seminar, I will first present the latest results on the evolution of a Bose-Einstein condensate after an abrupt compression where our preliminary analysis indicates an enhanced three-body losses.

Next, I will focus on describing a new experimental setup which aims to produce a 2D Bose gas of potassium-39 and explore the dynamics of quantum vortices in two dimensions.

Quantum hydrodynamics and turbulence in atomic BECs

Quantum hydrodynamics and turbulence [1] have been long studied in superfluid helium since 1950’s, and in atomic Bose-Einstein condensates (BECs) too. In this talk, I would discuss the important topics of atomic BECs.

Introduction

We will overview briefly characteristics of quantum hydrodynamics and turbulence compared with those of classical turbulence.

Single-component BECs

Turbulence likes isotropy [2] and rotation causes anisotropy. Such competition of two contradictory effects has been studied in classical turbulence [3]. Rotation in a quantum fluid forms a vortex lattice along the rotational axis and gives other interesting effects. There are not so many experimental works [4-6] on rotating quantum turbulence, and theoretical numerical studies are also limited [7]. I will discuss rotating quantum turbulence of BECs [8].

Two new scenarios for quantum friction: chiral media and rotating molecules

In the first scenario, we study the quantum friction experienced by a polarizable charged particle moving with parallel motion to a chiral medium-vacuum interface. We employ macroscopic quantum electrodynamics ^1,2 to obtain the Casimir–Polder frequency shift and decay rate. These results are a generalization of the respective quantities to matter being insensitive to parity². By examining the non-retarded and retarded limits we find that the an effective optical rotatory strength is relevant for a non-vanishing frequency shift and decay rate. For the second scenario, we investigate the rotational motion of diatomic molecules in free space interacting with the quantum electromagnetic field³. Using macroscopic quantum electrodynamics² we obtain the rotation-dependent decay rates of the molecule. By analyzing the behavior of the resulting rates at zero and finite temperature, we find a connection between the decelerating rotational dynamics and quantum friction.

¹ Stefan Yoshi Buhmann, David T. Butcher and Stefan Scheel. New Journal of Physics 14, 083034 (2012).
² S. Y. Buhmann. Dispersion Forces II. Many-Body Effects, Excited Atoms, Finite Temperature and Quantum Friction. (Springer, Berlin Heidelberg, 2012).
³ Stefan Yoshi Buhmann, M. R. Tarbutt, Stefan Scheel, and E. A. Hinds, Phys. Rev. A 78, 052901 (2008).

Non-stationary quantum many-body dynamics

Rydberg atoms in the vicinity of an optical nanofiber

Connecting atomic quantum registers via photonic channels into a quantum network is a promising way to achieve scalability, one of the crucial challenges in quantum technologies. Free-space scenarios considered so far are relatively easy to implement but suffer the drawback of strong losses. Optical nanowaveguides constitute an interesting alternative which offer strong transverse confinement of the field and hence strong coupling to atomic nodes in their vicinity. In particular optical nanofibers (ONFs) received much attention within the past two decades.

On the other hand, within the past two decades, the giant van der Waals interactions between Rydberg atoms and the associated blockade phenomenon have been key in many quantum information proposals, including atomic quantum registers and repeaters. In free-space, the energy shifts induced by the van der Waals interaction between two atoms prepared in levels of principal quantum numbers n > 50 and a few µm apart can be of the order of tens of GHz and effectively forbid their simultaneous resonant laser excitation. This blockade mechanism was employed to generate entanglement and perform gates in systems of individual atoms and atomic ensembles.

In this seminar, I shall present the theoretical results my collaborators and I obtained on the spontaneous emission and van der Waals interaction of rubidium atoms in the vicinity of a silica ONF [1,2] in view of building a Rydberg-atom-ONF interface. In particular, on the specific cases of S and P states, I shall analyze how the presence of the nanofiber and the symmetry breaking it induces modify the blockade and the anisotropy of the Rydberg-Rydberg interaction.

References

[1] E. Stourm, M. Lepers, J. Robert, S. Nic Chormaic, K. Mølmer, E. Brion, Spontaneous emission and energy shifts of a Rydberg rubidium atom close to an optical nanofiber, Phys. Rev. A 101, 052508 (2020).
[2] E. Stourm, M. Lepers, J. Robert, S. Nic Chormaic, K. Mølmer, E. Brion, Interaction of two Rydberg atoms in the vicinity of an optical nanofibre, New J. Phys. 25, 023022 (2023)

Quantum-Noise Reduction to improve Gravitational-Wave Detectors

Detection of gravitational waves by the Virgo detector requires exquisite control of all noise sources. In particular, a world-leading short-term frequency stability of the laser circulating in the interferometer on the mHz range is required for Virgo’s performance target [1].

The CALVA experiment at IJCLab is designed to study quantum states of light to improve Virgo’s performance. In particular, we are testing a method based on a Fabry-Perot cavity (filter cavity) for producing frequency-dependent squeezed states of light, which hold great promise for the future of gravitational-wave detectors [2]. This test requires excellent control of the laser frequency, at a level that would be compatible with Virgo’s performance. For this, we will use the ultra-stable frequency reference from the research infrastructure REFIMEVE, of which IJCLab is a member, and which is already available in the laboratory [3]. Because our laser has a different wavelength from the REFIMEVE signal (1064 nm vs. 1542 nm), an optical frequency comb is needed to transfer the stability of the ultra-stable signal to our laser.

The recent acquisition of an optical frequency comb by our team will enable a stability in the Hz range, improving our current stability by 3 orders of magnitude. This will help keep the CALVA experiment suitable for upcoming generations of gravitational-wave detectors, such as the Einstein Telescope project, not only in terms of performance, but also in terms of adaptability of the operating wavelength.

[1] F. Bondu, P. Fritschel, C. N. Man, and A. Brillet, Opt. Lett. 21, 582-584 (1996).
[2] C. M. Caves, Phys. Rev. D, 23:1693-1708 (1981).
[3] E. Cantin, M. Tønnes, R. L. Targat, A. Amy-Klein, O. Lopez, et P.-E. Pottie, New J. Phys. 23 (2021)

Effet Casimir Dynamique avec des atomes: de l’émission de paires de photons à une phase Sagnac quantique

L’interaction entre la matière et le champ électromagnétique quantique est particulièrement intrigante lorsque les effets de mouvement entrent en jeu. L’effet Casimir dynamique (ECD) est généralement considéré dans une approche macroscopique basée sur les conditions aux limites [1] pour le champ quantique. À un niveau microscopique plus fondamental, l’ECD peut être décrit à l’échelle atomique à l’aide de modèles hamiltoniens d’optique quantique pour le couplage atome-champ. Une observation expérimentale d’un analogue de l’ECD a été rapportée avec des supraconducteurs. Néanmoins, une mesure directe du rayonnement ECD produit par des corps en mouvement reste hors de portée car ce rayonnement est extrêmement faible dans des conditions expérimentales réalistes. Une voie alternative consiste à suivre des signatures indirectes d’aspects analogues à l’ECD dans les interféromètres atomiques, produites par le mouvement relatif entre l’atome et une surface conductrice. Dans cette présentation, nous présentons une théorie microscopique de l’effet Casimir dynamique [2,3], et utilisons ce formalisme pour prédire des effets analogues à l’ECD dans les interféromètres atomiques [4,5]. Notre approche révèle des connexions entre des aspects non triviaux de la physique moderne tels que la retardation électrodynamique, les phases géométriques, la non-localité et les effets non-inertiels.

La diffraction d’atomes rapides au dessus d’une surface cristalline

Découverte, il y a presque vingt ans la diffraction d’atomes légers entre 200 eV et 5 keV au dessus d’une surface trouve des applications pour le suivie de la croissance directement en bâti d’épitaxie ou elle permet un diagnostique fin du mode de croissance et de la topologie/reconstruction de la dernière couche. Je présenterai les évolutions récentes sur les processus inélastiques et les mesures des forces attractives vers la surface.

—

Diffraction of fast atoms above a crystalline surface.

Discovered almost twenty years ago, the diffraction of light atoms between 200 eV and 5 keV above a surface is finding applications in the monitoring of growth directly in the epitaxial frame, where it enables fine diagnosis of the growth mode and the topology/reconstruction of the last layer. I will present recent developments in inelastic processes and measurements of attractive forces towards the surface.

Laser absorption with non-resonance cavities and Faraday rotation spectroscopy for gas sensing applications, towards laboratory detection of OH and HO2 radicals.

Laser absorption spectroscopy is a fundamental technique widely used in trace gas sensing, with versatile applications in atmospheric chemistry, environmental monitoring, biomedical diagnostics, and molecular astrophysics. By quantifying the attenuation of light passing through a gas sample, this non-invasive method enables in-situ and absolute quantification of sample concentration. The utilization of optical cavities can significantly increase the light-sample interaction length, thereby enhancing detection limits according to the Beer-Lambert law. Among laser-based cavity techniques, off-axis Cavity-Enhanced Absorption Spectroscopy (off-axis CEAS) stands out as a robust approach for trace gas detection. A key feature of this approach involves eliminating the cavity mode structure through the un-resonance coupling of a narrow bandwidth laser source into a cavity, facilitating continuous scanning of laser frequency for rapid spectral measurements. This strategy offers simple optical alignment and circumvents the need for high-bandwidth devices or laser frequency-locking, ensuring robustness against misalignment and mechanical vibration.

In this work, we present the developments and applications of non-resonance cavities for the direct quantification of OH and HO2 radicals, key species in atmospheric chemistry. Furthermore, the enhancement of optical effective path length not only amplifies the absorption of the target molecules but also extends to common atmospheric species such as water vapor and CO2. The occurrence of spectral interference, resulting from the overlapping absorptions of various species, poses challenges in accurately determining the concentration of the species of interest. To address these challenges, we introduce Faraday Rotation Spectroscopy, leveraging the magneto-optic effect observed only for paramagnetic species (e.g., NO, NO2, OH, HO2) to facilitate interference-free measurements. The combination of the optical cavity and Faraday rotation technique enhances both sensitivity and selectivity for gas concentration determination.

Earth – Moon – Mars crustal attenuation properties comparison

Following its deployement at the surface of Mars, the SEIS seismometer of the NASA-InSight mission recorded tens of high-frequency Martian seismic events (> 1Hz) which we analyzed to characterize the attenuation properties of the Martian lithosphere from an Earth-Moon-Mars comparison perspective. The Martian waveforms are generally depolarized and show P and S arrivals with a gradual beginning, a broad maximum and a very long coda decay. These characteristics are highly reminiscent of the seismic wavefield in the terrestrial oceanic lithosphere at high frequency (Po and So above 2Hz), where the stratification of the absorption was used to estimate the Asthenosphere-lithosphere boundary (Takeuchi et al., 2017). To constrain the attenuation properties on Mars, we modeled the energy envelopes of the Martian events using a multiple-scattering approach in which we considered a stratification of the velocity and the attenuation properties in the medium. We observed that a simple model composed of a highly scattered crust and a weakly inhomogeneous mantle is sufficient to explain Martian events. We found that the Martian crustal diffusivity (10-12 km²/s) is similar to the estimation obtained in the lithosphere of the Atlantic Ocean (15–60 km²/s, Hannemann et al. 2022), but higher than the Lunar crust value (2 km²/s). The absorption attenuation results indicate that the Martian crust is globally dry ~ 10^-4 compared to the terrestrial crust ~ 10^-3. Our results suggest that the basaltic nature and the heterogeneities of the crust are the main source of the scattering in the Martian lithosphere unlike the extend of the fractures with depth observed on the Moon.

Experimental strategies to track conformational changes in the gas phase

Complex molecular ions, like synthetic polymers or biomolecules, also display complex conformational landscapes, in relation with their hierarchical structuration. Characterizing such complex landscapes also poses experimental challenges. Gas phase approaches, based on mass spectrometry allow some degree of simplification, by isolating species of well-defined composition and environment. However, gas-phase structure-sensitive techniques, often based on optical spectroscopy, are not easy to apply to large, flexible polymers. In this context, ion mobility spectrometry (IMS) is an interesting compromise, as a low-resolution structural probe applicable to large (bio-)molecular species. Indeed, the “collision cross sections” (CCS) determined by IMS-MS have been widely used to propose structures for protein complexes. Our group has proposed several strategies to exploit IMS-MS beyond CCS measurements. In particular we demonstrated that tandem IMS measurements could be used to explore the (photo-)isomerization of complex molecular systems. More recently, we developed approaches to follow the kinetics of conformational changes in such systems, and derive the associated thermodynamical quantities. This seminar will describe the principle of tandem ion mobility measurements, and give an overview of the approaches developed in our lab.

Rydberg excitons : a nonlinear optics perspective

For the last decade, highly excited (Rydberg) states of electron-hole bound states (excitons) in the semiconductor Cu2O have been showing more and more similarities with their atomic relatives, enabling solid-state Rydberg physics. After a rapid overview on Cu2O Rydberg excitons, I will focus on two recent experimental results where Rydberg-induced optical nonlinearities are central. In the first case, the giant interactions between Rydberg states are used to produce a large self-Kerr effect. This is directly observed with spatially-resolved interferometric imaging. In a second example, I will discuss very recent result where a second harmonic generation process is time-resolved with sub-picosecond resolution to directly unveil the Rydberg states lifetime along with several other intriguing dynamics.

Fiber based high power lasers for quantum computing applications

Observation of relaxation stages in out-of-equilibrium closed quantum systems

The temporal evolution of a non-equilibrium quantum system is the most crucial aspect of its dynamics. We introduce ro-translational excitations in an 87Rb Bose-Einstein condensate, which, under certain conditions, induces turbulence in the system . Once this non-equilibrium state is achieved, the system is allowed to evolve until it reaches equilibrium. Throughout this dynamical process, the characteristic particle cascade is observed, featured by the appearance of a power-law in the momentum distribution along with temporal windows of meta-stability showing the emergence of universal scaling. Subsequently, the system reaches a pre-thermalization stage with minimal variation, followed by a reverse cascade that forms a new condensate with fraction and temperature different from the initial one. This allows the assessment of various energy inputs during relaxation. The system is investigated under different initial excitations and represents a closed system suitable for exploring new physics related to the relaxation dynamics of non-equilibrium quantum systems.