Seminars

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: 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:  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: 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.