arXiv subjects

Abhik Kumar Saha

Publications and source records attributed to Abhik Kumar Saha.

9 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

Vibrational resonance in a one-dimensional dissipative Bose-Josephson junction

We investigate the linear and nonlinear response of a one-dimensional dissipative Bose-Josephson junction subjected simultaneously to a weak low-frequency probe and a rapidly oscillating high-frequency external drive. Starting from the dissipative two-mode Bose-Josephson equations, we derive an effective higher-order nonlinear equation for the population imbalance by retaining the leading nonlinear correction. Using time-scale separation and perturbative analysis, we obtain analytical expressions for both the linear response at the fundamental frequency and the nonlinear response at the second harmonic. We show that the high-frequency modulation modifies the effective potential landscape and dynamically breaks the symmetry around the stationary state, giving rise to a finite second-harmonic response that is absent without the rapidly oscillating field. Both the linear and nonlinear response amplitudes exhibit resonance-like enhancement for optimal values of the high-frequency driving strength. We further analyze the dependence of the resonance characteristics on interaction strength, dissipation, and driving parameters in both the zero-phase and $π$-phase modes and compare the analytical predictions with direct numerical simulations. Our results demonstrate a controllable mechanism toward realizing linear and nonlinear vibrational resonance in a one-dimensional dissipative Bose-Josephson junction and open new possibilities for controlling collective dynamics in driven ultracold bosonic systems.

cond-mat.quant-gas↗

arXiv2026

Information scrambling in all-to-all interacting models

Information scrambling is a hallmark of quantum chaos and thermalization in isolated quantum many-body systems. We investigate scrambling dynamics in the all-to-all interacting spin Sachdev-Ye-Kitaev (SYK)-$q$ model using both pure- and mixed-state entanglement measures. We show that von-Neumann and Rényi entropies exhibit rapid growth followed by saturation near Haar-random values, signaling efficient scrambling. The scrambling rate reveals a nontrivial dependence on the interaction order, system size, and Hamiltonian scaling. We further employ mixed-state entanglement as a powerful probe of information scrambling. We numerically find a universal relation between the Rényi-1/2 mutual information and entanglement negativity for minimal interaction order in the early growth regime. Furthermore, entanglement negativity displays a Page-curve-like behavior under unequal subsystem partitioning, characterized by the birth, spread, and eventual death of quantum correlations. Our results provide a generic description of information scrambling using entanglement dynamics in all-to-all interacting spin systems with multi-body interactions.

quant-ph↗

arXiv2024

Characterizing far from equilibrium states of the one-dimensional nonlinear Schr{ö}dinger equation

We use the mathematical toolbox of the inverse scattering transform to study quantitatively the number of solitons in far from equilibrium one-dimensional systems described by the defocusing nonlinear Schr{ö}dinger equation. We present a simple method to identify the discrete eigenvalues in the Lax spectrum and provide a extensive benchmark of its efficiency. Our method can be applied in principle to all physical systems described by the defocusing nonlinear Schr{ö}dinger equation and allows to identify the solitons velocity distribution in numerical simulations and possibly experiments.

nlin.PS↗

arXiv2022

Phase diffusion and fluctuations in a dissipative Bose-Josephson junction

We analyze the phase diffusion, quantum fluctuations and their spectral features of an one-dimensional Bose-Josephson junction (BJJ) coupled to a bosonic heat bath. We show the dependence of the phase diffusion coefficient on the on-site interaction parameter $U$ and the temperature in zero-phase and $π$-phase modes. We find that in the $π$-phase mode, the phase diffusion co-efficient as a function of $U$ decreases so long as $U$ is below a critical value while it increases above the critical value. This criticality of on-site interaction reflects a transition between Josephson oscillation and macroscopic quantum self-trapping (MQST) regime. Based on the thermal canonical Wigner distribution, we calculate the coherence factor to understand its dependence on temperature and on-site interaction energy in Josephson oscillation and MQST regime. Furthermore, we discuss coherent and incoherent spectral properties in connection with the fluctuations of the relative phase and the population imbalance in both zero and $π$-phase modes from weak to strong dissipation regime.

physics.atom-ph↗

arXiv2021

Dynamical phase diagram of a one dimensional Bose gas in a box with a tunable weak-link: from Bose-Josephson oscillations to shock waves

We study the dynamics of one-dimensional bosons trapped in a box potential, in the presence of a barrier creating a tunable weak-link, thus realizing a one dimensional Bose Josephson junction. By varying the initial population imbalance and the barrier height we evidence different dynamical regimes. In particular we show that at large barriers a two mode model captures accurately the dynamics, while for low barriers the dynamics involves dispersive shock waves and solitons. We study a quench protocol that can be readily implemented in experiments and show that self-trapping resonances can occur. This phenomenon can be understood qualitatively within the two-mode model.

cond-mat.quant-gas↗

arXiv2020

Parametric oscillations in a dissipative bosonic Josephson junction

We study the dynamics of a nonlinear dissipative bosonic Josephson junction (BJJ) with a time-dependent sinusoidal perturbation in interaction term. We demonstrate parametric resonance where the system undergoes sustained periodic oscillations even in the presence of dissipation. This happens when the frequency of the perturbation is close to twice the frequency of the unperturbed Josephson oscillations and the strength of perturbation exceeds a critical threshold. We have formulated the threshold conditions for parametric oscillations. To explore the nature of the oscillations, we carry out a multiple time scale analysis of the stability boundaries in terms of the V-shaped Arnold's tongue in the parameter space. Full numerical simulations have been performed for the zero-, running- and $π$-phase modes of nonlinear Josephson effect. Our results demonstrate that in $π$-phase mode, the system is capable of making a transition from regular parametric to chaotic parametric oscillations as one crosses the stability boundary. Also, the phase difference undergoes phase slip before executing sustained parametric oscillations.

quant-ph↗

arXiv2019

Modeling atom-atom interactions at low energy by Jost-Kohn potentials

More than 65 years ago, Jost and Kohn [R. Jost and W. Kohn, {Phys. Rev.} {\bf 87}, 977 (1952)] derived an explicit expression for a class of short-range model potentials from a given effective range expansion with the $s$-wave scattering length $a_s$ being negative. For $a_s >0$, they calculated another class of short-range model potentials [R. Jost and W. Kohn, { Dan. Mat. Fys. Medd} {\bf 27}, 1 (1953)] using a method based on an adaptation from Gelfand-Levitan theory [I. M. Gel'fand and B. M. Levitan, { Dokl. Akad. Nauk. USSR} {\bf 77}, 557-560 (1951)] of inverse scattering. We here revisit the methods of Jost and Kohn in order to explore the possibility of modeling resonant finite-range interactions at low energy. We show that the Jost-Kohn potentials can account for zero-energy resonances. The $s$-wave phase shift for positive scattering length is expressed in an analytical form as a function of the binding energy of a bound state. We show that, for small binding energy, both the scattering length and the effective range are strongly influenced by the binding energy; and below a critical binding energy the effective range becomes negative provided the scattering length is large. As a consistency check, we carry out some simple calculations to show that Jost-Kohn potentials can reproduce the standard results of contact interaction in the limit of the effective range going to zero.

physics.atom-ph↗

arXiv2019

The effects of trap-confinement and interatomic interactions on Josephson effects and macroscopic quantum self-trapping for a Bose-Einstein Condensate

We theoretically study the effects of trap-confinement and interatomic interactions on Josephson oscillations (JO) and macroscopic quantum self-trapping (MQST) for a Bose-Einstein condensate (BEC) confined in a trap which has a symmetric double-well (DW) potential along z-axis and 2D harmonic potentials along x- and y-axis. We consider three types of model interaction potentials: contact, long-range dipolar and finite-range potentials. Our results show that by changing the aspect ratio between the axial and radial trap sizes, one can induce a transition from JO to MQST for contact interactions with a small scattering length. For long-range dipolar interatomic interactions, we analyze transition from Rabi to Josephson regime and Josephson to MQST regime by changing the aspect ratio of the trap for a particular dipolar orientation. For a finite-range interaction, we study the effects of relatively large scattering length and effective range on JO and MQST. We show that JO and MQST are possible even if scattering length is relatively large, particularly near a narrow Feshbach resonance due to the finite-range effects.

physics.atom-ph↗