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Sadhan K. Adhikari

Publications and source records attributed to Sadhan K. Adhikari.

At least 55 records · Page 3Linked to original sources
arXiv2005

Bound states of attractive Bose-Einstein condensates in shallow traps in two and three dimensions

Using variational and numerical solutions of the mean-field Gross-Pitaevskii equation for attractive interaction (with cubic or Kerr nonlinearity) we show that a stable bound state can appear in a Bose-Einstein condensate (BEC) in a localized exponentially-screened radially-symmetric harmonic potential well in two and three dimensions. We also consider an axially-symmetric configuration with zero axial trap and a exponentially-screened radial trap so that the resulting bound state can freely move along the axial direction like a soliton. The binding of the present states in shallow wells is mostly due to the nonlinear interaction with the trap playing a minor role. Hence these BEC states are more suitable to study the effect of the nonlinear force on the dynamics. We illustrate the highly nonlinear nature of breathing oscillation of these states. Such bound states could be created in BECs and studied in the laboratory with present knowhow.

cond-mat.other↗
arXiv2005

Evolution of a collapsing and exploding Bose-Einstein condensate in different trap symmetries

Based on the time-dependent Gross-Pitaevskii equation we study the evolution of a collapsing and exploding Bose-Einstein condensate in different trap symmetries to see the effect of confinement on collapse and subsequent explosion, which can be verified in future experiments. We make prediction for the evolution of the shape of the condensate and the number of atoms in it for different trap symmetries (cigar to pancake) as well as in the presence of an optical lattice potential. We also make prediction for the jet formation in different cases when the collapse is suddenly terminated by changing the scattering length to zero via a Feshbach resonance.

cond-mat.other↗
arXiv2004

Stabilization of a (3+1)D soliton in a Kerr medium by a rapidly oscillating dispersion coefficient

Using the numerical solution of the nonlinear Schroedinger equation and a variational method it is shown that (3+1)-dimensional spatiotemporal optical solitons can be stabilized by a rapidly oscillating dispersion coefficient in a Kerr medium with cubic nonlinearity. This has immediate consequence in generating dispersion-managed robust optical soliton in communication as well as possible stabilized Bose-Einstein condensates in periodic optical-lattice potential via an effective-mass formulation. We also critically compare the present stabilization with that obtained by a rapid sinusoidal oscillation of the Kerr nonlinearity parameter.

nlin.PS↗
arXiv2004

Mean-field description of dynamical collapse of a fermionic condensate in a trapped boson-fermion mixture

We suggest a time-dependent dynamical mean-field-hydrodynamic model for the collapse of a trapped boson-fermion condensate and perform numerical simulation based on it to understand some aspects of the experiment by Modugno et al. [Science 297, 2240 (2002)] on the collapse of the fermionic condensate in the 40K-87Rb mixture. We show that the mean-field model explains the formation of a stationary boson-fermion condensate at zero temparature with relative sizes compatible with experiment. This model is also found to yield a faithful representation of the collapse dynamics in qualitative agreement with experiment. In particular we consider the collapse of the fermionic condensate associated with (a) an increase of the number of bosonic atoms as in the experiment and (b) an increase of the attractive boson-fermion interaction using a Feshbach resonance. Suggestion for experiments of fermionic collapse using a Feshbach resonance is made.

cond-mat.other↗
arXiv2004

Stabilization of bright solitons and vortex solitons in a trapless three-dimensional Bose-Einstein condensate by temporal modulation of the scattering length

Using variational and numerical solutions of the mean-field Gross-Pitaevskii equation we show that a bright soliton can be stabilized in a trapless three-dimensional attractive Bose-Einstein condensate (BEC) by a rapid periodic temporal modulation of scattering length alone by using a Feshbach resonance. This scheme also stabilizes a rotating vortex soliton in two dimensions. Apart from possible experimental application in BEC, the present study suggests that the spatiotemporal solitons of nonlinear optics in three dimensions can also be stabilized in a layered Kerr medium with sign-changing nonlinearity along the propagation direction.

cond-mat.other↗
arXiv2004

Mean-field model of jet formation in a collapsing Bose-Einstein condensate

We perform a systematic numerical study, based on the time-dependent Gross-Pitaevskii equation, of jet formation in collapsing and exploding Bose-Einstein condensates as in the experiment by Donley et al [2001 Nature 412 295]. In the actual experiment, via a Feshbach resonance, the scattering length of atomic interaction was suddenly changed from positive to negative on a pre-formed condensate. Consequently, the condensate collapsed and ejected atoms via explosion. On a disruption of collapse by suddenly changing the scattering length to zero a radial jet of atoms was formed in the experiment. We present a satisfactory account of jet formation under the experimental conditions as well as make predictions beyond experimental conditions which can be verified in future experiments.

cond-mat.soft↗
arXiv2003

Bright vortex solitons in Bose Condensates

We suggest the possibility of observing and studying bright vortex solitons in attractive Bose-Einstein condensates in three dimensions with a radial trap. Such systems lie on the verge of critical stability and we discuss the conditions of their stability. We study the interaction between two such solitons. Unlike the text-book solitons in one dimension, the interaction between two radially trapped and axially free three-dimensional solitons is inelastic in nature and involves exchange of particles and deformation in shape. The interaction remains repulsive for all phase delta between them except for delta \approx 0.

cond-mat.soft↗
arXiv2003

Bose-Einstein Condensation Dynamics from the Numerical Solution of the Gross-Pitaevskii Equation by the Pseudospectral Method

We study certain stationary and time-evolution problems of trapped Bose-Einstein condensates of weakly interacting alkali atoms described by a nonlinear Gross-Pitaevskii (GP) equation. We suggest a pseudospectral method involving Laguerre polynomials to solve the time dependent GP for a spherically symmetric trap potential. The radial wavefunction and energy values have been calculated for different nonlinearities. Further, we study the effect of suddenly changing the interatomic scattering length or harmonic oscillator trap potential in the condensate. We also investigate the frequency of oscillation due to the variation in the strength of nonlinearity.

cond-mat.soft↗
arXiv2003

Mean-field model of interaction between bright vortex solitons in Bose-Einstein condensates

Using the explicit numerical solution of the axially-symmetric Gross-Pitaevskii equation we study the dynamics of interaction among vortex solitons in a rotating matter-wave bright soliton train in a radially trapped and axially free Bose-Einstein condensate to understand certain features of the experiment by Strecker et al.[2002 Nature 417 150]. In a soliton train, solitons of opposite phase (phase delta = pi) repel and stay apart without changing shape; solitons with delta = 0 attract, interact and coalesce, but eventually come out; solitons with a general delta usually repel but interact inelastically by exchanging matter. We study and suggest future experiments with vortex solitons.

cond-mat.soft↗
arXiv2003

Coulomb three-body systems and charge transfer collisions in a configuration-space approach

Some low-energy three-body muon- and electron-transfer processes are considered within the Faddeev-Hahn formulation using two-, six-, and ten-state close-coupling approximation. We test our approach in bound-state problems for systems H$_2^+$ and ($μ^-$dd)$^+$ within six- and ten-state schemes, where $d$ is a deuteron and $μ$ a muon. We present results in the six-state model for muonium formation from hydrogen. We also present results for muon-transfer rates from muonic hydrogen isotopes to bare nuclei S$^{16}$ and Ar$^{18}$ in reasonable agreement with experiment. For these heavier targets a polarization potential is included and Coulomb potentials are treated exactly without approximation or cut off.

physics.atm-clus↗
arXiv2003

Matter-wave interference, Josephson oscillation and its disruption in a Bose-Einstein condensate on an optical lattice

Using the axially-symmetric time-dependent mean-field Gross-Pitaevskii equation we study the Josephson oscillation in a repulsive Bose-Einstein condensate trapped by a harmonic plus an one-dimensional optical-lattice potential to describe the experiments by Cataliotti et. al. [Science 293 (2001) 843, New J. Phys. 5 (2003) 71.1]. After a study of the formation of matter-wave interference upon releasing the condensate from the optical trap, we directly investigate the alternating atomic superfluid Josephson current upon displacing the harmonic trap along the optical axis. The Josephson current is found to be disrupted upon displacing the harmonic trap through a distance greater than a critical distance signaling a superfluid to a classical insulator transition in the condensate.

cond-mat.soft↗
arXiv2003

Expansion of a Bose-Einstein condensate formed on a joint harmonic and one-dimensional optical-lattice potentials

We study the expansion of a Bose-Einstein condensate trapped in a combined optical-lattice and axially-symmetric harmonic potentials using the numerical solution of the mean-field Gross-Pitaevskii equation. First, we consider the expansion of such a condensate under the action of the optical-lattice potential alone. In this case the result of numerical simulation for the axial and radial sizes during expansion is in agreement with two experiments by Morsch et al.[2002 Phys. Rev. A 66 021601(R) and 2003 Laser Phys. 13 594]. Finally, we consider the expansion under the action of the harmonic potential alone. In this case the oscillation and the disappearance and revival of the resultant interference pattern is in agreement with the experiment by Müller et al. [2003 J. Opt. B 5 538].

cond-mat.soft↗
arXiv2003

Critical number of atoms in an attractive Bose-Einstein condensate on an optical plus harmonic traps

The stability of an attractive Bose-Einstein condensate on a joint one-dimensional optical lattice and an axially-symmetric harmonic trap is studied using the numerical solution of the time-dependent mean-field Gross-Pitaevskii equation and the critical number of atoms for a stable condensate is calculated. We also calculate this critical number of atoms in a double-well potential which is always greater than that in an axially-symmetric harmonic trap. The critical number of atoms in an optical trap can be made smaller or larger than the corresponding number in the absence of the optical trap by moving a node of the optical lattice potential along the axial direction of the harmonic trap. This variation of the critical number of atoms can be observed experimentally and compared with the present calculation.

cond-mat.soft↗
arXiv2003

Dynamical classical superfluid-insulator transition in a Bose-Einstein condensate on an optical lattice

We predict a dynamical classical superfluid-insulator transition in a Bose-Einstein condensate (BEC) trapped in a combined optical and axially-symmetric harmonic potentials initiated by a periodic modulation of the radial trapping potential. The transition is marked by a loss of phase coherence in the BEC and a subsequent destruction of the interference pattern upon free expansion. For a weak modulation of the radial potential the phase coherence is maintained. For a stronger modulation and a longer time of holding in the modulated trap, the phase coherence is destroyed signaling a classical superfluid-insulator transition. The results are illustrated by a complete numerical solution of the axially-symmetric mean-field Gross-Pitaevskii equation for a repulsive BEC. Suggestion for future experiment is made.

cond-mat.soft↗
arXiv2003

Loss of superfluidity in a Bose-Einstein condensate via forced resonant oscillations

We predict the loss of superfluidity in a Bose-Einstein condensate in an axially symmetric harmonic trap alone during resonant collective oscillations via a classical dynamical transition. The forced resonant oscillation can be initiated by (a) a periodic modulation of the atomic scattering length with a frequency that equals twice the radial trapping frequency or multiples thereof, or by (b) a periodic modulation of the radial trapping potential with a frequency that equals the radial trapping frequency or multiples thereof. Suggestion for future experiment is made.

cond-mat.soft↗
arXiv2003

Mean-field model for Josephson oscillation in a Bose-Einstein condensate on an one-dimensional optical trap

Using the axially-symmetric time-dependent Gross-Pitaevskii equation we study the phase coherence in a repulsive Bose-Einstein condensate (BEC) trapped by a harmonic and an one-dimensional optical lattice potential to describe the experiment by Cataliotti {\it et al.} on atomic Josephson oscillation [Science {\bf 293}, 843 (2001)]. The phase coherence is maintained after the BEC is set into oscillation by a small displacement of the magnetic trap along the optical lattice. The phase coherence in the presence of oscillating neutral current across an array of Josephson junctions manifests in an interference pattern formed upon free expansion of the BEC. The numerical response of the system to a large displacement of the magnetic trap is a classical transition from a coherent superfluid to an insulator regime and a subsequent destruction of the interference pattern in agreement with the more recent experiment by Cataliotti {\it et al.} [e-print cond-mat/0207139].

cond-mat.soft↗
arXiv2003

Loss of superfluidity in a Bose-Einstein condensate on an optical lattice via a novel classical phase transition

We predict the loss of superfluidity in a Bose-Einstein condensate (BEC) trapped in a combined optical and axially-symmetric harmonic potentials during a resonant collective excitation initiated by a periodic modulation of the atomic scattering length $a$, when the modulation frequency equals twice the radial trapping frequency or multiples thereof. This classical dynamical transition is marked by a loss of superfluidity in the BEC and a subsequent destruction of the interference pattern upon free expansion. Suggestion for future experiment is made.

cond-mat.soft↗