arXiv subjects

Nicolas Cherroret

Publications and source records attributed to Nicolas Cherroret.

At least 19 recordsLinked to original sources

arXiv2026

Critical non-thermal fixed point and the dynamical condensation phase transition

Using a non-perturbative quantum kinetic framework, we develop a unified description of the far-from-equilibrium dynamics of three-dimensional Bose gases following cooling quenches across the Bose-Einstein condensation transition. By tracking the spatio-temporal evolution of the momentum distribution, we show that the equilibrium condensation threshold simultaneously acts as a dynamical critical point, separating distinct far-from-equilibrium universality classes governed by different non-equilibrium attractors. While quenches above the transition exhibit a single-timescale relaxation toward a thermal fixed point, quenches below the transition display a crossover from a transient weak-turbulence regime to a coarsening fixed point governed by the diffusive recombination of vortex lines. Quenches directly to the condensation threshold, finally, are controlled by a previously unidentified critical fixed point characterized by the superdiffusive spreading of critical fluctuations and a distinct set of dynamical exponents. Together, these dynamical scaling laws establish a far-from-equilibrium counterpart of the condensation phase transition, in which the equilibrium critical point also organizes the long-time non-equilibrium dynamics.

cond-mat.quant-gas↗

arXiv2026

Entanglement entropy across the dynamical phase transition in the quantum $\mathcal{O}(N)$ model

We demonstrate that the dynamical phase transition of the quantum $\mathcal{O}(N)$ model at large $N$ leaves universal fingerprints in the infrared structure of the entanglement spectrum. While the leading contribution to the entanglement entropy at long time follows the conventional volume law associated with ballistic entanglement spreading, its subleading behavior sharply distinguishes the different dynamical regimes. Specifically, quenches at and below the critical point generate gapless low-energy entanglement modes together with logarithmic corrections to the long-time entanglement entropy, whose scaling is governed by the scaling exponent of the transition. Using an infinite-slab bipartition geometry and exact numerical correlation functions in the large-$N$ limit, we characterize these scaling laws across the dynamical phase diagram and relate them to the emergence of long-range correlations during the post-quench dynamics. We further show that the entanglement eigenmodes themselves reveal characteristic signatures of the dynamical phase transition through their spatio-temporal structure and degeneracy properties.

quant-ph↗

arXiv2026

Energy-resolved transport of ultracold atoms across the Anderson transition: theory and experiment

In a recent experiment [X. Yu et al., arXiv:2602.07654], energy-resolved measurements of an atomic matter wave spreading in a speckle potential enabled the direct observation of the three-dimensional Anderson transition. In this work, we present a quantitative theoretical description of the matter-wave dynamics based on a tailored implementation of the self-consistent theory of localization, which incorporates both the spectral and spatial properties of the state prepared in the disorder. We benchmark this theoretical approach against ab initio numerical simulations, and use it to analyze the atom density profiles observed experimentally in the localized, diffusive, and critical regimes. Particular emphasis is placed on the key role of the atomic energy distribution, especially on the distinct contributions of Bose-condensed and thermal atoms to interpret the experimental profiles. Our framework provides a versatile and efficient theoretical toolbox for quantitatively describing wave-packet dynamics in three-dimensional disordered quantum systems, which remain challenging for state-of-the-art large-scale numerical simulations.

cond-mat.quant-gas↗

arXiv2026

Direct Observation of the Three-Dimensional Anderson Transition with Ultracold Atoms in a Disordered Potential

Anderson localization of particles -- the complete halt of wave transport through multiple scattering and phase coherence -- is a paradigmatic manifestation of quantum interference in disordered media. In three dimensions, the scaling theory predicts a quantum phase transition at a critical energy, the mobility edge, separating localized from diffusive states and underpinning metal-insulator transitions in electronic systems. Despite decades of experimental efforts, a direct observation of this emblematic transition for matter waves has remained elusive. Previous attempts with ultracold atoms were hindered by strong and uncontrolled energy broadening, resulting in indirect, sometimes inaccurate, and model-dependent estimates of the mobility edge. Here we implement a novel energy-resolved scheme to prepare atomic matter waves with a narrow energy distribution and track their expansion dynamics over long timescales. This allows for a direct observation of the three-dimensional Anderson transition in a laser-speckle disordered potential, and for a precise measurement of the mobility edge that is independent of any underlying theoretical modeling. Our measurements show excellent agreement with state-of-the-art numerical predictions over a wide range of disorder strengths, resolving long-standing discrepancies between prior experiments and theory. Beyond the three-dimensional Anderson transition, our approach opens new avenues for quantitative investigations of quantum critical phenomena in spatially disordered systems, including the roles of dimensionality, symmetry class, and interactions.

cond-mat.quant-gas↗

arXiv2026

Critical speed of a binary superfluid of light

We theoretically study the critical speed for superfluid flow of a two-dimensional miscible binary superfluid of light past a polarization-sensitive optical obstacle. This speed corresponds to the maximum mean flow velocity below which dissipation is absent. In the weak-obstacle regime, linear-response theory shows that the critical speed is set by Landau's criterion applied to the density and spin Bogoliubov modes, whose relative ordering can be inverted due to saturation of the optical nonlinearity. For obstacles of arbitrary strength and large spatial extent, we determine the critical speed from the conditions for strong ellipticity of the stationary hydrodynamic equations within the hydraulic and incompressible approximations. Numerical simulations in this regime reveal that the breakdown of superfluidity is initiated by the nucleation of vortex-antivortex pairs for an impenetrable obstacle, and of Jones-Roberts solitons for a penetrable obstacle. Beyond superfluids of light, our results provide a general framework for the critical speed of two-dimensional binary nonlinear Schr\"odinger superflows, including Bose-Bose quantum mixtures.

cond-mat.quant-gas↗

arXiv2025

From percolation transition to Anderson localization in one-dimensional speckle potentials

Classical particles in random potentials typically experience a percolation phase transition, being trapped in clusters of mean size $\chi$ that diverges algebraically at a percolation threshold. In contrast, quantum transport in random potentials is controlled by the Anderson localization length, which shows no distinct feature at this classical critical point. Here, we present a comprehensive theoretical analysis of the semi-classical crossover between these two regimes by studying particle propagation in a one-dimensional, red speckle potential, which hosts a percolation transition at its upper bound. As the system deviates from the classical limit, we find that the algebraic divergence of $\chi$ continuously connects to a smooth yet non-analytic increase of the localization length. We characterize this behavior both numerically and theoretically using a semi-classical approach. In this crossover regime, the correlated and non-Gaussian nature of the speckle potential becomes essential, causing the standard Dorokhov-Mello-Pereyra-Kumar (DPMK) description for uncorrelated disorder to break down. Instead, we predict the emergence of a bimodal transmission distribution, a behavior normally absent in one dimension, which we capture within our semi-classical analysis. Deep in the quantum regime, the DMPK framework is recovered and the universal features of Anderson localization reappear.

cond-mat.dis-nn↗

arXiv2025

Phonon scattering from spatial relaxation of one-dimensional Bose gases

We theoretically investigate the nonequilibrium relaxation of a spatial density modulation in a one-dimensional, weakly interacting Bose gas, and its connection to the equilibrium scattering rate $\smash{\gamma_k\propto k^{3/2}}$ of the system's phononic excitations. We show that the relaxation is generally governed by a nonequilibrium scattering rate $\gamma_{k,t}$ coupled to quantum fluctuations, which approaches its equilibrium value $\gamma_k$ only at long times. Numerical simulations of quantum kinetic equations reveal an algebraic convergence, $\smash{\gamma_{k,t} - \gamma_k \sim t^{-2/3}}$, confirmed by analytical predictions. More broadly, our results establish a theoretical framework for experimentally probing phonon dynamics through the temporal evolution of local perturbations in quantum gases.

cond-mat.quant-gas↗

arXiv2025

Coarsening of binary Bose superfluids: an effective theory

We derive an effective equation of motion for binary Bose mixtures, which generalizes the Cahn-Hilliard description of classical binary fluids to superfluid systems. Within this approach, based on a microscopic Hamiltonian formulation, we show that the domain growth law $L(t)\sim t^{2/3}$ observed in superfluid mixtures is not driven by hydrodynamic flows, but arises from the competition between interactions and quantum pressure. The effective theory allows us to derive key properties of superfluid coarsening, including domain growth and Porod's laws. This provides a new theoretical framework for understanding phase separation in superfluid mixtures.

cond-mat.quant-gas↗

arXiv2024

Spin and Density Modes in a Binary Fluid of Light

We present the experimental observation of spin and density modes in a binary mixture of superfluids of light. A miscible Bose-Bose mixture with repulsive interactions is obtained by propagating, in the paraxial limit, the two circular polarization components of a laser through a non-linear hot atomic vapor. Controlling the intensity and phase for both polarizations allows us to selectively excite the fundamental modes of the mixture. Using a Bragg-like spectroscopy technique, we measure the dispersion relation and identify two distinct branches with different speeds of sound corresponding to the spin and density modes. At large photon density, we observe a crossing of these branches, which is due to an effective photon-photon interaction beyond the two-body regime and related to the saturation of the medium nonlinearity. This novel degree of freedom allows for precise control over the ratio of spin and density sound velocities and provide new insights into the control of binary mixtures collective dynamics.

cond-mat.quant-gas↗

arXiv2024

From inverse-cascade to sub-diffusive dynamic scaling in driven disordered Bose fluids

We explore the emergence of universal dynamic scaling in an interacting Bose gas around the condensation transition, under the combined influence of an external driving force and spatial disorder. As time progresses, we find that the Bose gas crosses over three distinct dynamical regimes: (i) an inverse turbulent cascade where interactions dominate the drive, (ii) a stationary regime where the inverse cascade and the drive counterbalance one other, and (iii) a sub-diffusive cascade in energy space governed by the drive and disorder, a phenomenon recently observed experimentally. We show that all three dynamical regimes can be described by self-similar scaling laws.

cond-mat.quant-gas↗

arXiv2024

Anomalous Landau damping and algebraic thermalization in two-dimensional superfluids far from equilibrium

We present a quantitative description of the thermalization dynamics of far-from-equilibrium, two-dimensional (2D) Bose superfluids. Our analysis leverages a quantum kinetic formalism and allows us to identify two successive regimes of relaxation: an initial damping of quasi-particles due to Landau scattering processes, followed by the slower establishment of a global equilibrium at long time. For a far-from-equilibrium initial state, we find that Landau damping differs from the conventional picture of exponentially relaxing quasi-particles. Moreover, our results showcase a pronounced mechanism of algebraic transport at late times, rooted in energy conservation and compatible with 2D diffusion. Using theoretical and numerical arguments, we construct a detailed dynamical portrait of global equilibration in 2D superfluids.

cond-mat.quant-gas↗

arXiv2023

Berezinskii approach to disordered spin systems with asymmetric scattering and application to the quantum boomerang effect

We extend the Berezinskii diagrammatic technique to one-dimensional disordered spin systems, in which time-reversal invariance is broken due to a spin-orbit coupling term inducing left-right asymmetric scattering. We then use this formalism to theoretically describe the dynamics of the quantum boomerang effect, a recently discovered manifestation of Anderson localization. The theoretical results are confirmed by exact numerical simulations of wave-packet dynamics in a random potential.

cond-mat.dis-nn↗

arXiv2023

Time Translation Symmetry Breaking in an Isolated Spin-Orbit-Coupled Fluid of Light

We study the interplay between intrinsic spin-orbit coupling and nonlinear photon-photon interactions in a nonparaxial, elliptically polarized fluid of light propagating in a bulk Kerr medium. We find that in situations where the nonlinear interactions induce birefringence, i.e., a polarization-dependent nonlinear refractive index, their interplay with spin-orbit coupling results in an interference between the two polarization components of the fluid traveling at different wave vectors, which entails the breaking of translation symmetry along the propagation direction. This phenomenon leads to a Floquet band structure in the Bogoliubov spectrum of the fluid, and to characteristic oscillations of its intensity correlations. We characterize these oscillations in detail and point out their exponential growth at large propagation distances, revealing the presence of parametric resonances.

physics.optics↗

arXiv2023

Resonant Spin Hall Effect of Light in Random Photonic Arrays

It has been recently shown that the coherent component of light propagating in transversally disordered media, the so-called coherent mode, exhibits an optical spin Hall effect (SHE). In non-resonant materials, however, this phenomenon shows up at a spatial scale much larger than the mean free path, making its observation challenging due to the exponential attenuation of the coherent mode. Here, we show that in disordered photonic arrays exhibiting Mie resonances, the SHE on the contrary appears at a scale smaller than the mean free path if one operates in the close vicinity of the lowest transverse-magnetic resonance of the array. In combination with a weak measurement, this gives rise to a giant SHE that should be observable in optically-thin media. Furthermore, we show that by additionally exploiting the cooperative emission of a flash of light following the abrupt extinction of the incoming beam, one can achieve a time-dependent SHE, observable at large optical thickness as well.

physics.optics↗

arXiv2023

Dynamical phase transition of light in time-varying nonlinear dispersive media

We demonstrate the existence of a prethermal dynamical phase transition (DPT) for fluctuating optical beams propagating in nonlinear dispersive media. The DPT can be probed by suddenly changing in time the dispersion and nonlinearity parameters of the medium (thus realizing a "temporal interface"), a procedure that emulates a quench in a massive $φ^4$ model. Above a critical value of the quench identifying the transition, the fluctuating beam after the temporal interface is characterized by a correlation length that diverges algebraically at the transition. Below the critical quench, the beam exhibits an algebraic relaxation and a self-similar scaling. Our analysis also reveals a dimensional cross-over of the critical exponent, a characteristic feature of the optical DPT.

physics.optics↗

arXiv2023

Quantum kinetics of quenched two-dimensional Bose superfluids

We study theoretically the non-equilibrium dynamics of a two-dimensional (2D) uniform Bose superfluid following a quantum quench, from its short-time (prethermal) coherent dynamics to its long-time thermalization. Using a quantum hydrodynamic description combined with a Keldysh field formalism, we derive quantum kinetic equations for the low-energy phononic excitations of the system and characterize both their normal and anomalous momentum distributions. We apply this formalism to the interaction quench of a 2D Bose gas and study the ensuing dynamics of its quantum structure factor and coherence function, both recently measured experimentally. Our results indicate that in two dimensions, a description in terms of independent quasi-particles becomes quickly inaccurate and should be systematically questioned when dealing with non-equilibrium scenarios.

cond-mat.quant-gas↗

arXiv2022

Low-energy prethermal phase and crossover to thermalization in nonlinear kicked rotors

In the presence of interactions, periodically-driven quantum systems generically thermalize to an infinite-temperature state. Recently, however, it was shown that in random kicked rotors with local interactions, this long-time equilibrium could be strongly delayed by operating in a regime of weakly fluctuating random phases, leading to the emergence of a metastable thermal ensemble. Here we show that when the random kinetic energy is smaller than the interaction energy, this system in fact exhibits a much richer dynamical phase diagram, which includes a low-energy pre-thermal phase characterized by a light-cone spreading of correlations in momentum space. We develop a hydrodynamic theory of this phase and find a very good agreement with exact numerical simulations. We finally explore the full dynamical phase diagram of the system and find that the transition toward full thermalization is characterized by relatively sharp crossovers.

cond-mat.quant-gas↗

arXiv2022

Dynamical emergence of a Kosterlitz-Thouless transition in a disordered Bose gas following a quench

We study the dynamical evolution of a two-dimensional Bose gas after a disorder potential quench. Depending on the initial conditions, the system evolves either to a thermal or a superfluid state. Using extensive quasi-exact numerical simulations, we show that the two phases are separated by a Kosterlitz-Thouless transition. The thermalization time is shown to be longer in the superfluid phase, but no critical slowing down is observed at the transition. The long-time phase diagram is well reproduced by a simple theoretical model. The spontaneous emergence of Kosterlitz-Thouless transitions following a quench is a generic phenomenon that should arise both in the context of non-equilibrium quantum gases and nonlinear, classical wave systems.

cond-mat.quant-gas↗