arXiv subjects

Gohar Hovhannesyan

Publications and source records attributed to Gohar Hovhannesyan.

5 recordsLinked to original sources

arXiv2026

Two-photon-assisted collisions in ultracold gases of polar molecules II : Optical shielding of ultracold polar molecular collisions

We theoretically investigate the collisions between ultracold polar molecules in the presence of two lasers ensuring a Raman resonant transition on individual molecules to suppress photon scattering, taking the example of bosonic $^{23}$Na$^{39}$K molecules. By varying laser detunings and intensities, we enable a repulsive long-range interaction potential between molecules. After solving a set of coupled Schrödinger equations with the Hamiltonian written in the basis of laser-dressed states of the molecule pair at infinite distance, we identify quasi-resonant conditions under which elastic collisions are favored over inelastic and reactive ones, by a factor of about 2, thus demonstrating a promising pathway for efficient two-photon optical shielding of ultracold molecular collisions. The results are analyzed in terms of scattering length of the colliding laser-dressed molecules, which exhibit prominent resonances assigned to the interaction of the entrance channel with other specific channels, consistent with the existence of a quasi-bound level of the long-range molecular pair induced by the lasers.

cond-mat.quant-gas↗

arXiv2025

Two-photon-assisted collisions in ultracold gases of polar molecules

We present a theoretical formalism to treat the ultracold dynamics of a pair of colliding polar molecules submitted to two laser fields. We express the dressed Hamiltonian including the dipole-dipole interaction of the colliding molecular pair, both in their ground and electronic excited states, as well as their interaction with the two laser fields. We apply adiabatic elimination of the electronic excited state to reduce the size of the dressed-state basis in which the dressed Hamiltoninan is expressed. In an application, we investigate the feasibility of two-photon collisional shielding between two \NaK molecules, which could be favored by the Raman resonance condition suppressing unwanted spontaneous emission and photon scattering. We demonstrate the influence of the laser Rabi frequencies on the dynamics through the computation of elastic, inelastic, and reactive collision rates.

cond-mat.quant-gas↗

arXiv2023

Extension of Judd-Ofelt theory: Application on Eu$^{3+}$, Nd$^{3+}$ and Er$^{3+}$

We present a modified version of the Judd-Ofelt theory, which describes the intensities of f-f transitions for trivalent lanthanide ions (Ln$^{3+}$) in solids. In our model, the properties of the dopant are calculated with well-established atomic-structure techniques, while the influence of the crystal-field potential is described as a perturbation, by three adjustable parameters. Compared to our previous work [G. Hovhannesyan \textit{et al.}, J. Lumin. \textbf{241}, 118456 (2022)], the spin-orbit interaction within the first excited configuration 4f$^{w-1}$5d is described in a perturbative way, whereas it is exactly taken into account in the ground configuration 4f$^w$, using all the eigenvector components of the free-ion levels. Moreover, the wavelength-dependence of the refractive index of the host material is also accounted for. We test the validity of our model on three ions: Eu$^{3+}$, Nd$^{3+}$ and Er$^{3+}$. The results of the extension are satisfactory, we are able to give a physical insight into all the transitions within the ground electronic configuration, and also to reproduce quantitatively experimental absorption oscillator strengths. We also performed calculations of standard JO parameters, and the results are in good agreement with the values reported in the literature. The code used to make the calculations is available on GitLab.

physics.atom-ph↗

arXiv2023

Improving the spectroscopic knowledge of neutral Neodymium

Laser cooling and trapping of lanthanides has opened the possibility to carry out new experiments with ultracold dipolar gases, for example for quantum simulation of solid state physics. To identify new suitable candidates for laser-cooling, it is important to have a precise spectroscopic knowledge of the atom under consideration. Along this direction, we present here a detailed modeling of the energy levels of neutral neodymium (Nd), an element belonging to the left part of the lanthanide row, which has not yet been considered for laser-cooling. Using the semi-empirical method implemented in the Cowan suite of codes, we are in particular able to interpret more than 200 experimental levels of the NIST database belonging to both parities. The optimal set of atomic parameters obtained after the least-square fitting step can serve to calculate radiative transition probabilities in the future.

physics.atom-ph↗

arXiv2021

Transition intensities of trivalent lanthanide ions in solids: Revisiting the Judd-Ofelt theory

We present a modified version of the Judd-Ofelt theory, which describes the intensities of f-f transitions by trivalent lanthanide ions (Ln$^{3+}$) in solids. In our model, the properties of the dopant are calculated with well-established atomic-structure techniques, while the influence of the crystal-field potential is described by three adjustable parameters. By applying our model to europium (Eu$^{3+}$), well-known to challenge the standard Judd-Ofelt theory, we are able to give a physical insight into all the transitions within the ground electronic configuration, and also to reproduce quantitatively experimental absorption oscillator strengths. Our model opens the possibility to interpret polarized-light transitions between individual levels of the ion-crystal system.

cond-mat.mtrl-sci↗