arXiv subjects

Arnaldo Gammal

Publications and source records attributed to Arnaldo Gammal.

At least 19 recordsLinked to original sources

arXiv2026

Dynamics of one-dimensional Bose-Josephson Junction in a Box Trap: From Coherent Oscillations to Many-Body Dephasing and Dynamical Freezing

Understanding how coherent quantum dynamics give way to correlation-dominated behavior in low-dimensional systems remains a central challenge in quantum many-body physics. Here, we investigate a one-dimensional Bose-Josephson junction confined in a box trap using the multiconfigurational time-dependent Hartree method for bosons (MCTDHB). By varying the interaction strength and initial population imbalance, we identify distinct dynamical regimes governed by the competition between coherence and correlation-induced fragmentation. Weak interactions support coherent Josephson oscillations, whereas increasing imbalance leads to damping. At intermediate interaction strength, varying only the initial imbalance induces a crossover from nearly pure coherent oscillations to many-body dephasing with collapse-and-revival dynamics, and ultimately to equilibration accompanied by strong fragmentation and the saturation of many-body observables. In the strongly interacting regime, the system enters a dynamical freezing regime characterized by pronounced fragmentation, well-separated particle-resolved density peaks, and strongly suppressed tunneling. A systematic comparison with the Bose-Hubbard model reveals excellent agreement in the weakly interacting regime, while progressively larger deviations emerge as higher-orbital occupations beyond the two-mode approximation become significant. These results provide a unified picture of the emergence and competition of coherence, many-body dephasing, equilibration, and dynamical freezing, while delineating the regime of validity of the Bose-Hubbard description.

cond-mat.quant-gas↗

arXiv2026

Weakly interacting Bose gases in the canonical ensemble

Based on the canonical description of a non-interacting Bose gas, we work out how both thermodynamic and statistical properties change perturbatively with respect to weak two-particle interactions. Up to first order, we obtain a recursion formula for the canonical partition function, which consists of the same Feynman diagrams as the grand-canonical description but with different Feynman rules. Resumming this recursion formula for the canonical partition function allows one to characterize the statistics of the ground-state occupancy by its respective cumulants. We demonstrate the applicability of this approach by analyzing a dilute Bose gas with contact interaction in a box trap. To this end, we used Dirichlet boundary conditions in view of their relevance for current experiments with atomic gases, where the box trap is implemented, for instance, with digital mirror devices.

cond-mat.quant-gas↗

arXiv2026

Negative Interaction Quench Dynamics of Density-Ordered Dipolar Bosons in a One-Dimensional Optical Lattice

We explore the nonequilibrium dynamics of a density-ordered dipolar Bose gas in a finite one-dimensional optical lattice following a negative interaction quench, using the numerically exact multiconfigurational time-dependent Hartree method for bosons. The interaction sign reversal, effectively driving a crossover from long-range to short-range interactions, generates rich intra- and interwell tunneling dynamics spanning superfluid, Mott-insulating, and fragmented regimes. A striking finding is the robustness of the underlying crystal-state correlations against the quench, despite the strong dynamical response. We identify emergent excitation modes, including local breathing and dipole-like oscillations, via real- and momentum-space observables, and quantify tunneling through site-resolved position variance. One- and two-body Glauber correlation functions further uncover a direct connection between tunneling and correlation dynamics. Moreover, we show that combining interaction quenches with lattice-depth ramping enables controllable dynamical engineering, establishing dipolar lattice systems as a promising platform for nonequilibrium quantum simulation.

cond-mat.quant-gas↗

arXiv2026

Stability of dark solitons in a bubble Bose-Einstein condensate

The stability of nonlinear waves on curved surfaces is a problem of widespread interest across physics. Here, we establish the stability criteria for dark solitons on a spherical Bose-Einstein condensate. We demonstrate a sharp instability threshold in the nonlinear parameter, beyond which solitons decay into vortex dipoles via snake instabilities. Analytically and numerically, we prove this decay is dictated by a single unstable mode for each angular momentum $m \geq 2$, which is a universal mechanism that controls the resulting vortex state. Unlike in the full three-dimensional case, where snake instabilities lead to vortex rings, a dark soliton confined to the surface of a bubble can only decay into vortex pairs.

cond-mat.quant-gas↗

arXiv2026

Immiscible to miscible quenching instabilities in two-dimensional binary Bose-Einstein condensates

Immiscible to miscible quenching transitions (IMQT) in homogeneous Bose-Einstein condensate are investigated, considering rubidium isotopes $^{85}$Rb and $^{87}$Rb confined in a two-dimensional (2D) circular box, under two different initial configurations. These IMQT instabilities, triggered by sudden reductions in the two-body interspecies scattering length $a_{12}$, are explored under two distinct initialconditions, highlighting the critical role of nonlinear dynamics in their evolution. The numerical simulations indicate that the instability dynamics are primarily driven by the production of large vortices and the propagation of sound waves (phonons), with sound wave excitations prevailing in the long-term evolution. The compressible and incompressible parts of the kinetic energy spectra, in terms of the wave number $k$, are confronted with the classical Kolmogorov scaling, $k^{-5/3}$ for turbulence, which is observed in the onset of instabilities. Before reaching the ultraviolet dissipation region at small scales, the IMQT spectra exhibit a bottleneck effect, indicating a clear departure from classical scaling behavior. In the time asymptotic miscible regime, it is observed that the vorticity and sound-wave production remain practically stable. In this regime, for both cases investigated, a linear relation is also recognized between the miscibility parameter and the initial IMQT configuration.

cond-mat.quant-gas↗

arXiv2025

Rayleigh-Taylor, Kelvin-Helmholtz and immiscible to miscible quenching instabilities in binary Bose-Einstein condensates

We investigate three kinds of instabilities in binary immiscible homogeneous Bose-Einstein condensate, considering rubidium isotopes $^{85}$Rb and $^{87}$Rb confined in two-dimensional circular box. Rayleigh-Taylor (RT) and Kelvin-Helmholtz (KH) instability types are studied under strong perturbations. Without external perturbation, instabilities are also probed by immiscible to miscible quenching transition (IMQT), under two different initial configurations. Our numerical simulations show that all such instability dynamics are dominated by large vortex productions and sound-wave (phonon) propagations. For long-term propagation, vortex dynamics become dominant over sound waves in the KH instability, while sound wave excitations predominate in the other cases. For all the dynamical simulations, the emergence of possible scaling laws are investigated for the compressible and incompressible parts of the kinetic energy spectra, in terms of the wave number $k$. The corresponding results are compared with the classical Kolmogorov scalings, $k^{-5/3}$ and $k^{-3}$, for turbulence, which are observed in the kinetic energy spectra at some specific time intervals. Deviating from the classical scaling, a kind of ``Bottleneck effect" is noticed in the IMQT spectra.

cond-mat.quant-gas↗

arXiv2025

Localization versus incommemsurability for finite boson system in one-dimensional disordered lattice

We explore the effect of disorder on a few-boson system in a finite one-dimensional quasiperiodic potential covering the full interaction ranging from uncorrelated to strongly correlated particles. We apply numerically exact multiconfigurational time-dependent Hartree for bosons to obtain the few-body emergent states in a finite lattice for both commensurate and incommensurate filling factors. The detailed characterization is done by the measures of one- and two-body correlations, fragmentation, order parameter. For commensurate filling, we trace the conventional fingerprints of disorder induced localization in the weakly interacting limit, however we observe robustness of fragmented and strongly correlated Mott in the disordered lattice. For filling factor smaller than one, we observe existing delocalization fraction of particles interplay in a complex way. For strongly interacting limit, the introduced disorder drags the fragmented superfluid of primary lattice to Mott localization. For filling factor larger than one in the primary lattice, the extra delocalization always resides on commensurate background of Mott-insulator. We observe beyond Bose-Hubbard physics in the fermionization limit when the pairing bosons fragment into two orbitals -- Mott dimerization happens. The introduced disorder first relocates the dimers, then strong disorder starts to interfere with the background Mott correlation. These findings unlock a rich landscape of unexplored localization process in the quasiperiodic potentials and pave the way for engineering exotic quantum many-body states with ultracold atoms.

cond-mat.quant-gas↗

arXiv2025

Transport of ultracold dipolar fermions in one-dimensional optical lattices

We investigate the transport properties in out-of-equilibrium dynamics of strongly correlated dipolar fermions initially localized in one-dimensional inhomogeneous optical lattice. The dynamics is studied by experimentally measurable dynamical variables such as one-body density, pair-correlation function and size of the expanding cloud. In the noninteracting limit, we trace the usual fingerprints of ballistic expansion in the short time dynamics. However, dynamics is strongly affected by system size due to Pauli principle. The dynamics also exhibits significant dependence on the sign of the interactions. We observe that strong repulsive dipolar interaction gives rise to many-body features in the dynamics, while strong attractive dipolar interaction leads to stabilized cluster states. Intermediate dipolar interaction are found to hinder expansion of correlations, while very strong dipolar interaction favors expansion of the cloud. Our work show the effect of dipolar interaction in the transport properties of interacting fermions, that can be studied in on-going experiments with ultracold dipolar fermions.

cond-mat.quant-gas↗

arXiv2024

One-Dimensional Quench Dynamics in an Optical Lattice: sine-Gordon and Bose-Hubbard Descriptions

We investigate the dynamics of one-dimensional interacting bosons in an optical lattice after a sudden quench in the Bose-Hubbard (BH) and sine-Gordon (SG) regimes. While in higher dimension, the Mott-superfluid phase transition is observed for weakly interacting bosons in deep lattices, in 1D an instability is generated also for shallow lattices with a commensurate periodic potential pinning the atoms to the Mott state through a transition described by the SG model. The present work aims at identifying the SG and BH regimes. We study them by dynamical measures of several key quantities. We numerically exactly solve the time dependent Schrödinger equation for small number of atoms and investigate the corresponding quantum many-body dynamics. In both cases, correlation dynamics exhibits collapse revival phenomena, though with different time scales. We argue that the dynamical fragmentation is a convenient quantity to distinguish the dynamics specially near the pinning zone. To understand the relaxation process we measure the many-body information entropy. BH dynamics clearly establishes the possible relaxation to the maximum entropy state determined by the Gaussian orthogonal ensemble of random matrices (GOE). In contrast, the SG dynamics is so fast that it does not exhibit any signature of relaxation in the present time scale of computation.

cond-mat.quant-gas↗

arXiv2024

Strongly interacting bosons in 1D disordered lattice: phase coherence of distorted Mott phases

We explore the consequences of disorder on phase coherence in the Mott insulator phases in an optical lattice. Few bosons with contact interaction in small optical lattice can feature varieties of insulating phases: weakly interacting Mott in deep lattice, maximally fragmented and strongly interacting Mott in intermediate lattice, weak Mott with double filling and intra-well coherence, fermionized Mott with strong intra-well coherence. Utilization of the multiconfigurational time dependent Hartree method for bosons (MCTDHB) to solve the many-boson Schroedinger equation, facilitates to understand the microscopic effect of disorder on the different kinds of Mott phases in the primary lattice. The many-body properties are analyzed by distinct measures of the reduced one-body density in real and momentum space, fragmentation, order parameter, variance of spatial single-shot measurements, compressibility and the Glauber normalized correlation functions. We find very complex competition of localization due to disorder and Mott correlation. We observe distinct response of four different Mott phases in the disordered lattice. When the weakly interacting Mott exhibits the Bose Glass phase, the strongly correlated and fully fragmented Mott exhibits leakage, melting and central localization. In contrast, weak Mott with double filling which is a spatially separated dimer in each site, exhibits only some dissociation of intra-well coherence and assist in the development of inter-well coherence in the presence of strong disorder. For the fermionized Mott, when the density in each well is fragmented, strong disorder interfere with the intra-well correlation and the characteristic dip in each site starts to disappear leading to simple Mott localization with a pair of bosons.

cond-mat.quant-gas↗

arXiv2024

Quasi-superfluid and Quasi-Mott phases of strongly interacting bosons in shallow optical lattice

We explore the ground states of strongly interacting bosons in the vanishingly small and weak lattices using the multiconfiguration time-dependent Hartree method for bosons (MCTDHB) which calculate numerically exact many-body wave function. Two new many-body phases: fragmented or quasi superfluid (QSF) and incomplete fragmented Mott or quasi Mott insulator (QMI) are emerged due to the strong interplay between interaction and lattice depth. Fragmentation is utilized as a figure of merit to distinguish these two new phases. We utilize the eigenvalues of the reduced one-body density matrix and define an order parameter that characterizes the pathway from a very weak lattice to a deep lattice. We provide a detailed investigation through the measures of one- and two-body correlations and information entropy. We find that the structures in one- and two-body coherence are good markers to understand the gradual built-up of intra-well correlation and decay of inter-well correlation with increase in lattice depth.

cond-mat.quant-gas↗

arXiv2024

Quantum information theoretic measures to distinguish fermionized bosons from non-interacting fermions

We study the dynamical fermionization of strongly interacting one-dimensional bosons in Tonks-Girardeau limit by solving the time dependent many-boson Schrödinger equation numerically exactly. We establish that the one-body momentum distribution approaches the ideal Fermi gas distribution at the time of dynamical fermionization. The analysis is further complemented by the measures on two-body level. Investigation on two-body momentum distribution, two-body local and non-local correlation clearly distinguish the fermionized bosons from non-interacting fermions. The magnitude of distinguishablity between the two systems is further discussed employing suitable measures of information theory, i.e., the well known Kullback-Leibler relative entropy and the Jensen-Shannon divergence entropy. We also observe very rich structure in the higher-body density for strongly correlated bosons whereas non-interacting fermions do not possess any higher order correlation beyond two-body.

cond-mat.quant-gas↗

arXiv2023

Faraday waves on a bubble Bose-Einstein condensed binary mixture

By studying the dynamic stability of Bose-Einstein condensed binary mixtures trapped on the surface of an ideal two-dimensional spherical bubble, we show how the Rabi coupling between the species can modulate the interactions leading to parametric resonances. In this spherical geometry, the discrete unstable angular modes drive both phase separations and spatial patterns, with Faraday waves emerging and coexisting with an immiscible phase. Noticeable is the fact that, in the context of discrete kinetic energy spectrum, the only parameters to drive the emergence of Faraday waves are the $s-wave$ contact interactions and the Rabi coupling. Once analytical solutions for population dynamics are obtained, the stability of homogeneous miscible species is investigated through Bogoliubov-de Gennes and Floquet methods, with predictions being analysed by full numerical solutions applied to the corresponding time-dependent coupled formalism.

cond-mat.quant-gas↗

arXiv2023

Out of equilibrium many-body expansion dynamics of strongly interacting bosons

We solve the Schrödinger equation from first principles to investigate the many-body effects in the expansion dynamics of one-dimensional repulsively interacting bosons released from a harmonic trap. We utilize the multiconfigurational time-dependent Hartree method for bosons (MCTDHB) to solve the many-body Schrödinger equation at high level of accuracy. The MCTDHB basis sets are explicitly time-dependent and optimised by variational principle. We probe the expansion dynamics by three key measures; time evolution of one-, two- and three-body densities. We observe when the mean-field theory results to unimodal expansion, the many-body calculation exhibits trimodal expansion dynamics. The many-body features how the initially fragmented bosons independently spreads out with time whereas the mean-field pictures the expansion of the whole cloud. We also present the three different time scale of dynamics of the inner core, outer core and the cloud as a whole. We analyze the key role played by the dynamical fragmentation during expansion. A Strong evidence of the many-body effects is presented in the dynamics of two- and three-body densities which exhibit correlation hole and pronounced delocalization effect.

cond-mat.quant-gas↗

arXiv2022

Tsallis statistics and thermofractals: applications to high energy and hadron physics

We study the applications of non-extensive Tsallis statistics to high energy and hadron physics. These applications include studies of $pp$ collisions, equation of state of QCD, as well as Bose-Einstein condensation. We also analyze the connections of Tsallis statistics with thermofractals, and address some of the conceptual aspects of the fractal approach, which are expressed in terms of the renormalization group equation and the self-energy corrections to the parton mass. We associate these well-known concepts with the origins of the fractal structure in the quantum field theory.

hep-ph↗

arXiv2021

Stability of a Bose condensed mixture on a bubble trap

Stability and dynamical behavior of binary Bose-Einstein condensed mixtures trapped on the surface of a rigid spherical shell are investigated in the mean-field level, exploring the miscibility with and without vortex charges, considering repulsive and attractive interactions. In order to compute the critical points for the stability, we follow the Bogoliubov-de Gennes method for the analysis of perturbed solutions, with the constraint that initially the stationary states are in a complete miscible configuration. For the perturbed equal density mixture, of a homogeneous uniform gas and when hidden vorticity is verified, with the species having opposite azimuthal circulation, we consider small perturbation analysis for each unstable mode, providing a complete diagram with the intra- and inter-species interaction role on the stability of the miscible system. Finally, beyond small perturbation analysis, we explore the dynamics of some repulsive and attractive inter-species states by full numerical solutions of the time-dependent Gross-Pitaevskii equation.

cond-mat.quant-gas↗

arXiv2021

Effect of Rashba spin-orbit and Rabi couplings on the excitation spectrum of binary Bose-Einstein condensates

We present the collective excitation spectrum analysis of binary Bose-Einstein condensates (BECs) with spin-orbit (SO) and Rabi couplings in a quasi-two-dimensional system. In particular, we investigate the role of SO and Rabi coupling strengths in determining the dynamical stability of the coupled BECs using Bogoliubov-de Gennes (BdG) theory. Using the eigenergy of BdG spectrum, we confirm the existence of phonon, roton, and maxon modes with weak repulsive intra- and inter-species contact interactions. The depth of the minimum corresponding to the roton mode depends strongly on the coupling strength. We find that the increase of the SO coupling leads to instability, while the increase in the Rabi coupling stabilizes the system. Also the eigenvectors of BdG spectrum indicates the presence of density like mode in the stable regime and spin like modes in unstable regimes. A phase diagram demonstrating the stability regime in the plane of SO and Rabi coupling strengths is obtained. Finally, we complement the observation of the excitation spectrum with the direct numerical simulation results of coupled Gross-Pitaevskii equations.

cond-mat.quant-gas↗

arXiv2020

Breakup of rotating asymmetric quartic-quadratic trapped condensates

The threshold conditions for a rotating pancake-like asymmetric quartic-quadratic confined condensate to break in two localized fragments, as well as to produce giant vortex at the center within the vortex-pattern distributions, are investigated within the Thomas-Fermi (TF) approximation and exact numerical solution of the corresponding Gross-Pitaevskii (GP) formalism. By comparing the TF predictions with exact GP solutions, in our investigation with two different quartic-quadratic trap geometries, of particular relevance is to observe that the TF approach is not only very useful to display the averaged density distribution, but also quite realistic in establishing the critical rotational conditions for the breakup occurrence and possible giant-vortex formation. It provides almost exact results to define the contour of the condensate distribution, even for high rotating system, after the system split in two (still confined) clouds. The applicability of the Feynman rule to the vortex distribution (full-numerical GP solutions) is also being confirmed for these non-homogeneous asymmetric trap configurations. This study is expected to be relevant for manipulating the rotation and trap parameters in addition to Feshbach resonance techniques. It can also be helpful to define initial conditions for any further studies on dynamical evolution of vortex pattern distributions.

physics.atom-ph↗