arXiv subjects

Rhombik Roy

Publications and source records attributed to Rhombik Roy.

15 recordsLinked to original sources

arXiv2026

Hidden Ergodic Relaxation in the Quench Dynamics of a Bichromatic Mott Lattice

We investigate the nonequilibrium dynamics of strongly interacting bosons in a finite bichromatic Mott lattice following a sudden quench of the secondary lattice amplitude. The coefficient entropies and second R\'enyi entropy exhibit pronounced growth toward their Gaussian Orthogonal Ensemble (GOE) predictions from random-matrix theory, consistent with GOE-like statistical spreading in the employed multiconfigurational representation. In striking contrast, experimentally accessible observables, including the momentum distribution, fragmentation, and Glauber correlation functions, remain nearly unchanged throughout the evolution. For the sampled strong quenches, the coefficient entropies, second R\'enyi entropy, and the $N$-body coefficient spreading collapse onto a common relaxation trajectory that becomes largely independent of the perturbation strength. Our results reveal an emergent hidden ergodic relaxation beneath the persistent local Mott-like order. An effective embedded random-matrix model captures the qualitative crossover from restricted to extensive Hilbert-space spreading, providing an interpretive framework for the observed relaxation dynamics.

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.

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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

Inferring rotations using a bosonic Josephson junction

Rotation and quantum tunneling are fundamental concepts in physics, and their interplay in the ultracold atomic systems is of particular interest. In this theoretical work, we explore how tunneling dynamics in a bosonic Josephson junction are modified when the system is placed in a rotating, non-inertial frame. We show that the tunneling dynamics of ultracold bosons in a two-dimensional double-well potential offer an alternative pathway for inferring the rotation frequency. Using the mean-field and many-body analyses, we demonstrate that rotation strongly modifies the tunneling time period as well as the momentum and angular momentum dynamics. When the rotation axis passes through the center of the double well, the observables show distinct dynamical responses with increasing rotation frequency, enabling the rotation frequency to be assessed from changes in the tunneling dynamics. When the potential is displaced from the rotation axis, the rotation induces asymmetric tunneling and partial self-trapping, allowing both the rotation frequency and the displacement to be inferred. We further show that for an off-centered double well, the tunneling dynamics exhibit a pronounced orientation dependence, enabling the orientation of the double well to be inferred from the observed dynamics. The many-body analysis further shows that the depletion dynamics are strongly influenced by rotation, providing an additional tool for assessing the rotation frequency. Finally, we study the effect of time-dependent rotation in which the double well is gradually set into motion in the laboratory frame and identify distinct dynamical signatures that depend sensitively on the switching time. Together, these results establish a comprehensive framework for inferring the rotation frequency, radial displacement, and orientation directly from the tunneling dynamics.

cond-mat.quant-gas↗

arXiv2025

Dynamics and transport of Bose-Einstein condensates in bent potentials

The dynamics of bosons in curved geometries have recently attracted significant interest in quantum many-body physics. Leveraging recent experimental advances in tailored trapping landscapes, we investigate the quantum transport of weakly interacting bosons in two-dimensional bent trapping potentials, showing that geometry alone can serve as a precise control knob for tunneling dynamics. Using time-adaptive many-body simulations, complemented by mean-field analysis and exact diagonalization, we analyze both static and dynamical properties of bosons confined in the bent potential. We reveal how bending an initially straight channel induces a transition from density localization to delocalization and drives the buildup of correlations in the ground state. In the dynamics, the bent acts as a tunable barrier that enables controllable tunneling: weak curvature allows coherent tunnelling across the bend, while stronger bent suppresses transport and enhances self-trapping. The tunneling rate can be precisely tuned by geometric parameters, establishing bent traps as versatile platforms for geometry-controlled quantum transport.

cond-mat.quant-gas↗

arXiv2025

Interplay of asymmetry and fragmentation in the many-body tunneling dynamics of two-dimensional bosonic Josephson junctions

It is well known that the many-body tunneling of a bosonic condensate leads to (longitudinal) fragmentation along the tunneling direction. In this work, we prepare the initial ground state as a (transversely) fragmented system by introducing a barrier oriented orthogonally to the tunneling direction and allow it to tunnel through a two-dimensional longitudinally and transversely-asymmetric bosonic Josephson junctions. For a fixed barrier height, we find that the initial transversal fragmentation is essentially independent of the asymmetry along the tunneling direction but reduces when the asymmetry is oriented orthogonally to the junction. We investigate the interplay between the interference of fragmentations and asymmetry in the junction by analyzing the rate of density collapse in the survival probability, the uncertainty product, and the nontrivial dynamics of the occupation of the first excited orbital. The interference of fragmentations is quantified by the ratio between the reduction of transverse fragmentation and the development of longitudinal fragmentation. We show that asymmetry along the junction (orthogonal to the junction) delays (accelerates), compared to the symmetric potential, in obtaining the maximal interference of fragmentations. Notably, self-trapping opposes the interference, whereas a resonant tunneling condition enhances it. Overall, we demonstrate that the influence of asymmetry on the competition between longitudinal and transversal fragmentations, which together govern the macroscopic tunneling dynamics of interacting bosons, arises purely from the many-body effects and has no counterpart in the mean-field theory.

cond-mat.quant-gas↗

arXiv2025

Rotation-mediated bosonic Josephson junctions in position and momentum spaces

In ultracold atoms, bosons tunneling in a double-well potential can produce a typical Josephson junction in real space. A major advancement in quantum matter and simulations is anticipated by the recently found momentum-space Josephson junctions, which elucidates the supercurrent flow between spin-orbit coupled Bose-Einstein condensates at two distinct independent momentum states. For the first time, our study unveils specific protocols to engineer momentum-space Josephson dynamics for scalar bosons (or a single-component condensate) in a rotating frame through modulation of the geometry of a double-well trapping potential and rotation frequencies. In this setup, the rotation simultaneously results in effective double wells both in position and in momentum spaces, and the dynamics of the corresponding Josephson junctions is hosted in these double wells. Consequently, it is observed that the rotation generates momentum-space Josephson dynamics of the condensate along the transverse direction and position-space Josephson dynamics along the longitudinal direction; these effects are particularly noticeable for high rotation frequencies. Additionally, the rotation-induced momentum-space junctions are highly significant in both the mean-field and many-body dynamics. Our protocols offer a framework for investigating momentum-space Josephson junctions for single-component condensates in both theoretical and experimental contexts, as well as their significant applications in quantum mechanical devices.

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 Schr\"odinger 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

Rotation quenches in trapped bosonic systems

The ground state properties of strongly rotating bosons confined in an asymmetric anharmonic potential exhibit a split density distribution. However, the out-of-equilibrium dynamics of this split structure remain largely unexplored. Given that rotation is responsible for the breakup of the bosonic cloud, we investigate the out-of-equilibrium dynamics by abruptly changing the rotation frequency. Our study offers insights into the dynamics of trapped Bose-Einstein condensates in both symmetric and asymmetric anharmonic potentials under different rotation quench scenarios. In the rotationally symmetric trap, angular momentum is a good quantum number. This makes it challenging to exchange angular momentum within the system; hence, a rotation quench does practically not impact the density distribution. In contrast, the absence of angular momentum conservation in asymmetric traps results in more complex dynamics. This allows rotation quenches to either inject into or extract angular momentum from the system. We observe and analyze these intricate dynamics both for the mean-field condensed and the many-body fragmented systems. The dynamical evolution of the condensed system and the fragmented system exhibits similarities in several observables during small rotation quenches. However, these similarities diverge notably for larger quenches. Additionally, we investigate the formation and the impact of the vortices on the angular momentum dynamics of the evolving split density. All in all, our findings offer valuable insights into the dynamics of trapped interacting bosons under different rotation quenches.

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arXiv2024

Assessing small accelerations using a bosonic Josephson junction

Bosonic Josephson junctions provide a versatile platform for exploring quantum tunneling and coherence phenomena in ultracold atomic systems. While extensive research has examined the Josephson-junction dynamics in various double-well configurations, most studies have been limited to inertial reference frames. In the present work, we posed the question how placing a Josephson junction in a non-inertial reference frame would impact the quantum tunnelling. Our findings demonstrate that accelerating a Josephson junction alters the tunneling dynamics. Conversely, tunneling behavior can be used to assess the acceleration of the system. By analyzing the changes in physical properties, we can assess the acceleration of the double-well. We begin with the most simple non-inertial frame: moving with constant acceleration. The tunneling time decreases exponentially as acceleration increases, making it effective for measuring larger accelerations. However, for smaller accelerations, accurate assessment requires accounting for many-body depletion, which decreases linearly as acceleration rises. Next, we explore a more complex scenario where the acceleration is time dependent. In this case, the acceleration is mapped onto the tunneling time period and depletion, which again serve as predictors of acceleration. We go further by conducting a detailed analysis of the change in tunnelling dynamics when the system deviates from constant or zero acceleration. The quantitative analysis show that the depletion changes exponentially near constant acceleration, while around zero acceleration, the change follows a polynomial pattern. All in all, we quantify how the tunneling process, as well as the mean-field and many-body properties, evolve in a non-inertial system of increasing complexity.

cond-mat.quant-gas↗

arXiv2024

Expansion of strongly interacting dipolar bosons in 1D optical lattices

We numerically study the expansion dynamics of initially localized dipolar bosons in a homogeneous 1D optical lattice for different initial states. Comparison is made to interacting bosons with contact interaction. For shallow lattices the expansion is unimodal and ballistic, while strong lattices suppress tunneling. However for intermediate lattice depths a strong interplay between dipolar interaction and lattice depth occurs. The expansion is found to be bimodal, the central cloud expansion can be distinguished from the outer halo structure. In the regime of strongly interactions dipolar bosons exhibit two time scales, with an initial diffusion and then arrested transport in the long time; while strongly interacting bosons in the fermionized limit exhibit ballistic expansion. Our study highlights how different lattice depths and initial states can be manipulated to control tunneling dynamics.

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.

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arXiv2022

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

We solve the Schr\"odinger 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 Schr\"odinger 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.

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arXiv2022

Dynamics of order-disorder and complexity for interacting bosons in optical lattice

The present work reports on the dynamical measures of order, disorder and complexity for the interacting bosons in optical lattice. We report results both for the relaxed state as well as quench dynamics. Our key observations are: (1) Lattice depth can be taken as order-disorder parameter. (2) The superfluid to Mott insulator transition can be treated as `order-disorder' transition. Our main motivation is to find how the system organize by itself during quench and how it optimizes the complexity. We find dynamical measures of order and disorder are more sensitive tool than entropy measures. We specifically calculate the time scale of entry and exit of different phases during time evolution. Initially the system exhibits collapse revival trend, however gradually looses its ability to turn back to superfluid phase and finally Settle to Mott insulator phase.

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arXiv2021

Quantum dynamics of few dipolar bosons in a double-well potential

We study the few-body dynamics of dipolar bosons in one-dimensional double-wells. Increasing the interaction strength, by investigating one-body observables, we study in the considered few-body systems tunneling oscillations, self-trapping and the regime exhibting an equilibrating behaviour. The corresponding two-body correlation dynamics exhibits a strong interplay between the interatomic correlation due to non-local nature of the repulsion and the inter-well coherence. We also study the link between the correlation dynamics and the occupation of natural orbitals of the one-body density matrix.

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