arXiv subjects

Neelam Shukla

Publications and source records attributed to Neelam Shukla.

7 recordsLinked to original sources

arXiv2026

Scissors modes in generalized Gross-Pitaevskii equations

We investigate scissors modes in nonlinear systems with arbitrary power-law dependence of the nonlinear term. Through analytical derivation, we establish a general expression demonstrating that, in the Thomas-Fermi regime, the frequency of the scissors mode is independent of the specific form of the nonlinearity. We conclude that the scissors mode is a shear mode that does not probe the compressibility of the system, which depends on nonlinearity. To validate our findings, we perform numerical simulations of experimentally relevant Lee-Huang-Yang (LHY) systems. Our results illustrate the transition of the scissors mode frequency from the non-interacting to the strongly interacting (Thomas-Fermi) regime. Finally, we demonstrate that the scissors mode frequency remains clearly identifiable even under strong quenches, which should facilitate the experimental observation of our findings.

cond-mat.quant-gas↗

arXiv2025

Two- and three-body dispersion coefficients for interaction of Cu and Ag atoms with {Group} I, II, and XII elements

The mounting interest in conducting thorough analyses and studies of long-range interactions stems from their wide-ranging applications in cold atomic physics, making it a compelling area for research. In this work, we have evaluated long range van der Waals dispersion (vdW) interactions of Cu and Ag atoms with atoms of group I (Li, Na, K, Rb, Cs, and Fr), II (Be, Mg, Ca, Sr, and {Ba}), XII (Zn, Cd, and Hg) {as well as} singly charged ions of group II (Be$^+$, Mg$^+$, Ca$^+$, Sr$^+$, and {Ba$^+$}) and XII (Zn$^+$, Cd$^+$, and Hg$^+$) by calculating $C_6$(two-body) and $C_9$ (three-body) vdW dispersion coefficients. In order to obtain these $C_6$ and $C_9$ coefficients, we have evaluated the dynamic dipole polarizability of the considered atoms using appropriate relativistic methods and the sum-over-states approach. To ascertain the accuracy of our results, we have compared the evaluated static dipole polarizabilities of Cu and Ag atoms and their oscillator strengths for dominant transitions {with} available literature. The calculated values of $C_6$ dispersion coefficients have also been compared with the previously reported results.

physics.atom-ph↗

arXiv2024

Properties of a static dipolar impurity in a 2D dipolar BEC

We study a system of ultra cold dipolar Bose gas atoms confined in a two-dimensional (2D) harmonic trap with a dipolar impurity implanted at the center of the trap. Due to recent experimental progress in dipolar condensates, we focused on calculating properties of dipolar impurity systems that might guide experimentalists if they choose to study impurities in dipolar gases. We used the Gross-Pitaevskii formalism solved numerically via the split-step Crank-Nicolson method. We chose parameters of the background gas to be consistent with dysprosium (Dy), one of the strongest magnetic dipoles and of current experimental interest, and used chromium (Cr), erbium (Er), terbium (Tb), and Dy for the impurity. The dipole moments were aligned by an external field along what was chosen to be the z-axis, and studied 2D confinements that were perpendicular or parallel to the external field. We show density contour plots for the two confinements, 1D cross sections of the densities, calculated self-energies of the impurities while varying both number of atoms in the condensate and the symmetry of the trap. We also calculated the time evolution of the density of an initially pure system where an impurity is introduced. Our results found that while the self-energy increases in magnitude with increasing number of particles, it is reduced when the trap anisotropy follows the natural anisotropy of the gas, i.e., elongated along the z-axis in the case of parallel confinement. This work builds upon work done in Bose gases with zero-range interactions and demonstrates some of the features that could be found when exploring dipolar impurities in 2D Bose gases.

cond-mat.quant-gas↗

arXiv2024

Anisotropic potential immersed in a dipolar Bose-Einstein condensate

We study a modified three-dimensional Gross-Pitaevski equation that describes a static impurity in a dipolar Bose-Einstein condensate (BEC). Our focus is on the interplay between the shape of the impurity and the anisotropy of the medium manifested in the energy and the density of the system. Without external confinement, properties of the system are derived with basic analytical approaches. For a system in a harmonic trap, the model is investigated numerically, using the split-step Crank-Nicolson method. Our results demonstrate that the impurity would prefer to change its shape to accommodate the anisotropic character of the bath, in particular it would prefer to align itself with the direction of the dipoles. Our work complements studies of impurities in Bose gases with zero-range interactions, and paves the way for studies of dipolar polarons with a modified Gross-Pitaevski equation.

cond-mat.quant-gas↗

arXiv2022

Two-dipole and three-dipole interaction coefficients of GROUP XII elements

The study of long-range interactions is increasingly becoming essential due to its various applications in cold atomic physics. These interactions can be conveniently expressed in terms of dispersion coefficients. In the present work, theoretical calculations have been carried out to estimate the two-dipole ($C_6$) and three-dipole ($C_9$) dispersion coefficients between the group XII atoms and their ions, \textit{viz.}, Zn, Cd, Hg, Zn$^+$, Cd$^+$, and Hg$^+$. To obtain these coefficients, the dynamic dipole polarizabilities and reduced matrix elements required are evaluated using the relativistic methods for both the considered atoms and ions. Further, using the calculated matrix elements, the oscillator strengths corresponding to leading transitions and static dipole polarizabilities are determined. These are compared with the available values in the literature through which the accuracy of the present calculations ascertains. However, the oscillator strengths for few transitions of Zn, Cd, Hg, Zn$^+$, Cd$^+$, and Hg$^+$, are not reported earlier, and we have provided their values in this work. Thereafter, the dispersion $C_6$ and $C_9$ coefficients are calculated for various combinations of the group XII elements, and most of these coefficients were not reported earlier in the literature. Furthermore, the combinations for which the other theoretical and experimental values were available for comparison showed good agreement. We, therefore, believe that our results reported for $C_6$ and $C_9$ coefficients for various combinations of group XII elements are reliable.

physics.atom-ph↗

arXiv2022

Dispersion $C_3$ coefficients for physisorption of heavy ions and atoms with graphene and carbon nanotubes

In the present work, the calculations have been performed for dispersion interaction between heavy elements (Zn$^+$, Cd$^+$, Hg$^+$, Pb$^+$, Zn, Cd, Hg, and Pb) with graphene and carbon nanotubes by evaluating van der Waals $C_3$ coefficients using well-known Lifshitz theory. The dispersion coefficients are expressed in terms of reflection coefficients of graphene and carbon nanotubes which are calculated within the framework of Dirac model. In addition, accurate values of dynamic dipole polarizabilities at imaginary frequencies of considered ions and atoms which are vital, have been calculated using relativistic methods. The comparisons of our calculated static dipole polarizabilities for the considered elements with the values reported in the literature are also presented. The dispersion interactions of the considered heavy elements with the graphene and carbon nanotubes of different radii in a wide range of separation distances have been studied. The results have also been analysed with another subtle variable, i.e., gap parameter of graphene wall. The interaction coefficients obtained for both the materials, i.e., for graphene and carbon nanotubes are mutually compared and it is found that graphene can be said as preferable material for adsorption of these toxic heavy elements.

physics.atom-ph↗

arXiv2020

Two-dipole and three-dipole dispersion coefficients for interaction of alkaline-earth atoms with alkaline-earth atoms and alkaline-earth ions

Apropos to the growing interest in the study of long-range interactions which for their applications in cold atom physics, we have performed theoretical calculation for the two-dipole $C_6$ and three-dipole $C_9$ dispersion coefficients involving alkaline-earth atoms with alkaline-earth atoms and alkaline-earth ions. The $C_6$ and $C_9$ coefficients are expressed in terms of the dynamic dipole polarizabilities, which are calculated using relativistic methods. Thereafter, the calculated $C_6$ coefficients for the considered alkaline-earth atoms among themselves are compared with the previously reported values. Due to unavailability of any other earlier theoretical or experimental results, for the $C_6$ coefficients for alkaline-earth atoms with alkaline-earth ions and the $C_9$ coefficients, we have performed separate fitting calculations and compared. Our calculations match in an excellent manner with the fitting calculations. We have also reported the oscillator strengths for the leading transitions and static dipole polarizabilities for the ground states of the alkaline-earth ions, i.e., Mg$^+$, Ca$^+$, Sr$^+$, and Ba$^+$ as well as the alkaline-earth atoms, i.e., Mg, Ca, Sr, and Ba. These, when compared with the available experimental results, show good agreement.

physics.atom-ph↗