arXiv subjects

S K Adhikari

Publications and source records attributed to S K Adhikari.

11 recordsLinked to original sources

arXiv2025

Dynamically stable two- and four-droplet solitons in a very strongly dipolar NaCs condensate

A strongly dipolar Bose-Einstein condensate (BEC) of Dy atoms could sustain different types of states not possible in a non-dipolar BEC. Motivated by the observation of a very strongly dipolar condensate of NaCs molecules [N. Bigagli et al., Nature 631, 289 (2024)], with dipolar interaction stronger by more than an order of magnitude compared to that of Dy atoms, we demonstrate that in a very strongly dipolar NaCs BEC, it is possible to have a two- and a four-droplet metastable soliton, axially free along the polarization $z$ direction. In this study we employ imaginary-time propagation of an improved mean-field model, including the Lee-Huang-Yang interaction. The dipolar solitons are subject to an expulsive Gaussian potential at the center and a harmonic potential $-$ both acting in the $x$-$y$ plane. The phase-coherent solitons, possessing the isolated droplets, are free to move along the $z$ axis without any relative motion between the droplets. The dynamical stability and mobility of these solitons are demonstrated by real-time propagation employing the converged imaginary-time wave function as the initial state.

cond-mat.quant-gas↗

arXiv2021

Symbiotic solitons in a quasi-one- and quasi-two-dimensional spin-1 condensates

We study the formation of spin-1 symbiotic spinor solitons in a quasi-one- (quasi-1D) and quasi-two-dimensional (quasi-2D) hyper-fine spin $F=1$ ferromagnetic Bose-Einstein condensate (BEC). The symbiotic solitons necessarily have a repulsive intraspecies interaction and are bound due to an attractive interspecies interaction. Due to a collapse instability in higher dimensions, an additional spin-orbit coupling is necessary to stabilize a quasi-2D symbiotic spinor soliton. Although a quasi-1D symbiotic soliton has a simple Gaussian-type density distribution, novel spatial periodic structure in density is found in quasi-2D symbiotic SO-coupled spinor solitons. For a weak SO coupling, the quasi-2D solitons are of the $(-1, 0, +1)$ or $(+1, 0, -1)$ type with intrinsic vorticity and multi-ring structure, for Rashba or Dresselhaus SO coupling, respectively, where the numbers in the parentheses are angular momenta projections in spin components $F_z = +1, 0, -1$, respectively. For a strong SO coupling, stripe and superlattice solitons, respectively, with a stripe and square-lattice modulation in density, are found in addition to the multi-ring solitons. The stationary states were obtained by imaginary-time propagation of a mean-field model; dynamical stability of the solitons was established by real-time propagation over a long period of time. The possibility of the creation of such a soliton by removing the trap of a confined spin-1 BEC in a laboratory is also demonstrated.

cond-mat.quant-gas↗

arXiv2019

Stable multi-peak vector solitons in spin-orbit coupled spin-1 polar condensates

We demonstrate the formation of multi-peak three-component stationary stripe vector solitons in a quasi-one-dimensional spin-orbit-coupled hyper-fine spin $F = 1$ polar Bose-Einstein condensate. The present investigation is carried out through a numerical solution by imaginary-time propagation and an analytic variational approximation of the underlying mean-field Gross-Pitaevskii equation. Simple analytic results for energy and component densities were found to be in excellent agreement with the numerical results for solitons with more than 100 pronounced maxima and minima. The vector solitons are one of the two types: dark-bright-dark or bright-dark-bright. In the former a maximum density in component $ F_z = 0 $ at the center is accompanied by a zero in components $F_z = \pm 1$. The opposite happens in the latter case. The vector solitons are demonstrated to be mobile and dynamically stable. The collision between two such vector solitons is found to be quasi elastic at large velocities with the conservation of total density of each vector soliton. However, at very small velocity, the collision is inelastic with a destruction of the initial vector solitons. It is possible to observe and study the predicted SO-coupled vector solitons in a laboratory.

cond-mat.quant-gas↗

arXiv2019

Phase-separation of vector solitons in spin-orbit coupled spin-1 condensates

We study the phase-separation in three-component bright vector solitons in a quasi-one-dimensional spin-orbit-coupled hyper-fine spin $F=1$ ferromagnetic Bose-Einstein condensate upon an increase of the strength of spin-orbit (SO) coupling $p_x Σ_z$ above a critical value, where $p_x$ is the linear momentum and $Σ_z$ is the $z$-component of the spin-1 matrix. The bright vector solitons are demonstrated to be mobile and dynamically stable. The collision between two such vector solitons is found to be elastic at all velocities with the conservation of density of each vector soliton. The two colliding vector solitons repel at small separation and at very small colliding velocity, they come close and bounce back with the same velocity without ever encountering each other. This repulsion produced by SO coupling is responsible for the phase separation in a vector soliton for large strengths of SO coupling. { The collision dynamics is found to be completely insensitive to the relative phase of the colliding solitons.} However, in the absence of SO coupling, at very small velocity, the two colliding vector solitons attract each other and form a vector soliton molecule and the collision dynamics is sensitive to the relative phase as in scalar solitons. The present investigation is carried out through a numerical solution and an analytic variational approximation of the underlying mean-field Gross-Pitaevskii equation.

cond-mat.quant-gas↗

arXiv2019

Symmetry-breaking vortex-lattice of a binary superfluid in a rotating bucket

We study spontaneous-symmetry-broken phase-separated vortex lattice in a weakly interacting uniform rapidly rotating binary Bose superfluid contained in a quasi-two-dimensional circular or square bucket. For the inter-species repulsion above a critical value, the two superfluid components separate and form a demixed phase with practically no overlap in the vortex lattices of the two components, which will permit an efficient experimental observation of such vortices and study their properties. In case of a circular bucket with equal intra-species energies of the two components, the two components separate into two non-overlapping semicircular domains for all frequencies of rotation $Ω$ generating distinct demixed vortex lattices. In case of a binary Bose superfluid in both circular and square buckets, (a) the number of vortices increases linearly with $Ω$ in agreement with a suggestion by Feynman, and (b) the rotational energy in the rotating frame decreases quadratically with $Ω$ in agreement with a suggestion by Fetter.

cond-mat.quant-gas↗

arXiv2018

Improved effective-range expansions for small and large values of scattering length

The textbook effective-range expansion of scattering theory is useful in the analysis of low-energy scattering phenomenology when the scattering length $|a|$ is much larger than the range $R$ of the scattering potential: $|a|\gg R$. Nevertheless, the same has been used for systems where the scattering length is much smaller than the range of the potential, which could be the case in many scattering problems. We suggest and numerically study improved two-parameter effective-range expansions for the cases $|a| > R$ and $|a| < R$. The improved effective-range expansion for $|a| > R$ reduces to the textbook expansion for $|a|/R \gg 1$.

quant-ph↗

arXiv2018

A self-bound matter-wave boson-fermion quantum ball

We demonstrate the possibility of creating a self-bound stable three-dimensional matter-wave spherical boson-fermion quantum ball in the presence of an attractive boson-fermion interaction and a small repulsive three-boson interaction. The three-boson interaction could be attractive or repulsive whereas the fermions are taken to be in a fully-paired super-fluid state in the Bardeen- Cooper-Schreifer ( quasi-noninteracting weak-coupling) limit. We also include the Lee-Huang-Yang (LHY) correction to a repulsive bosonic interaction term. The repulsive three-boson interaction and the LHY correction can stop a global collapse while acting jointly or separately. The present study is based on a mean-field model, where the bosons are subject to a Gross-Pitaevskii (GP) Lagrangian functional and the fully-paired fermions are described by a Galilean-invariant density functional Lagrangian. The boson-fermion interaction is taken to be the mean-field Hartree interaction, quite similar to the interaction term in the GP equation. The study is illustrated by a variational and a numerical solution of the mean-field model for the boson-fermion $^7$Li- $^6$Li system.

cond-mat.quant-gas↗

arXiv2017

Elastic collision and breather formation of spatiotemporal vortex light bullets in a cubic-quintic nonlinear medium

The statics and dynamics of a stable, mobile three-dimensional (3D) spatiotemporal vortex light bullet in a cubic-quintic nonlinear medium with a focusing cubic nonlinearity above a critical value and any defocusing quintic nonlinearity is considered. The present study is based on an analytic variational approximation and a full numerical solution of the 3D nonlinear Schrödinger equation. The 3D vortex bullet can propagate with a constant velocity. Stability of the vortex bullet is established numerically and variationally. The collision between two vortex bullets moving along the angular momentum axis is considered. At large velocities the collision is quasi elastic with the bullets emerging after collision with practically no distortion. At small velocities two bullets coalesce to form a single entity called a breather.

nlin.PS↗

arXiv2017

Elastic collision and molecule formation of spatiotemporal light bullets in a cubic-quintic nonlinear medium

We consider the statics and dynamics of a stable, mobile three-dimensional (3D) spatiotemporal light bullet in a cubic-quintic nonlinear medium with a focusing cubic nonlinearity above a critical value and any defocusing quintic nonlinearity. The 3D light bullet can propagate with a constant velocity in any direction. Stability of the light bullet under a small perturbation is established numerically.We consider frontal collision between two light bullets with different relative velocities. At large velocities the collision is elastic with the bullets emerge after collision with practically no distortion. At small velocities two bullets coalesce to form a bullet molecule. At a small range of intermediate velocities the localized bullets could form a single entity which expands indefinitely leading to a destruction of the bullets after collision. The present study is based on an analytic Lagrange variational approximation and a full numerical solution of the 3D nonlinear Schrödinger equation.

cond-mat.quant-gas↗

arXiv2016

Two-dimensional bright and dark-in-bright dipolar Bose-Einstein condensate solitons on a one-dimensional optical lattice

We study the statics and dynamics of anisotropic, stable, bright and dark-in-bright dipolar quasi-two-dimensional Bose-Einstein condensate (BEC) solitons on a one-dimensional (1D) optical-lattice (OL) potential. These solitons mobile in a plane perpendicular to the 1D OL trap can have both repulsive and attractive contact interactions. The dark-in-bright solitons are the excited states of the bright solitons. The solitons, when subject to a small perturbation, exhibit sustained breathing oscillation. The dark-in-bright solitons can be created by phase imprinting a bright soliton. At medium velocities the collision between two solitons is found to be quasi elastic.The results are demonstrated by a numerical simulation of the three-dimensional mean-field Gross-Pitaevskii equation in three spatial dimensions employing realistic interaction parameters for a dipolar $^{164}$Dy BEC.

cond-mat.quant-gas↗

arXiv2014

Stable, mobile, dark-in-bright, dipolar Bose-Einstein condensate soliton

We demonstrate robust, stable, mobile, quasi-one-dimensional, dark-in-bright dipolar Bose-Einstein condensate (BEC) soliton with a notch in the central plane formed due to dipolar interaction for repulsive contact interaction. At medium velocity the head on collision of two such solitons is found to be quasi elastic with practically no deformation. A proposal for creating dipolar dark-in-bright solitons in laboratories by phase imprinting is also discussed. A rich variety of such solitons can be formed in dipolar binary BEC, where one can have a dark-in-bright soliton coupled to a bright soliton or two coupled dark-in-bright solitons. The findings are illustrated using numerical simulation in three spatial dimensions employing realistic interaction parameters for a dipolar 164Dy BEC and a binary 164Dy-162Dy BEC.

cond-mat.quant-gas↗