Searcharxiv⌕ Search

arXiv subjects

Arpita Rakshit

Publications and source records attributed to Arpita Rakshit.

9 recordsLinked to original sources
arXiv2026

Multichannel Quantum Defect Theory with Numerical Reference Functions: Applications to Cold Atomic Collisions

We develop a method for calculating multichannel wavefunctions in the spirit of quantum defect theory, based on numerically calculated reference functions. We benchmark the method by calculating cold collisional properties of $^{85}$Rb and $^6$Li in the presence of external magnetic fields tuned across specific $s$-wave Feshbach resonances and thereby reproducing known results. We then apply the method to calculate experimentally observed $d$-wave Feshbach resonance {[\textit{Phys. Rev. Lett.} {\bf 119}, 203402 (2017)]} %MDPI: Is this a reference citation? If so, please note that ref. citations are not allowed in Abstract and should be removed. in $^{87}$Rb-$^{85}$Rb cold collisions. Our numerical results for this $d$-wave resonance show good agreement with the experimental observations. The method is applicable to arbitrary interaction potentials and to any energy range near the scattering threshold. The implementation of our method to any multichannel two-body scattering problem is straightforward.

physics.chem-ph↗
arXiv2018

Structure, spectroscopy and cold collisions of the (SrNa)$^+$ ionic system

We perform a study on extended adiabatic potential energy curves of nearly 38 states of 1,3$Σ^+$, 1,3$Π$ and 1,3$Δ$ symmetries for the (SrNa)$^+$ ion, though only the ground and first two excited states are used for the study of scattering processes. Full Interaction Configuration (CI) calculations are carried out for this molecule using the pseudopotential approach. In this context, it is considered that two active electrons interact with the ionic cores and all single and double excitations were included in the CI calculations. A correction including the core-core electron interactions is also considered. Using the accurate potential energy data, the ground state scattering wave functions and cross sections are obtained for a wide range of energies. We find that, in order to get convergent results for the total scattering cross sections for energies of the order 1 K, one need to take into account at least 87 partial waves. In the low energy limit ( < 1 mK), elastic scattering cross sections exhibit Wigner law threshold law behavior while in the high energy limit the cross sections go as $E^{-1/3}$. A qualitative discussion about the possibility of forming the cold molecular ion by photoassociative spectroscopy is presented.

physics.atom-ph↗
arXiv2016

Interactions and low energy collisions between an alkali ion and an alkali atom of different nucleus

We study theoretically interaction potentials and low energy collisions between different alkali atoms and alkali ions. Specifically, we consider systems like X + Y$^{+}$, where X(Y$^{+})$ is either Li(Cs$^+$) or Cs(Li$^+$), Na(Cs$^+$) or Cs(Na$^+$) and Li(Rb$^+$) or Rb(Li$^+$). We calculate the molecular potentials of the ground and first two excited states of these three systems using pseudopotential method and compare our results with those obtained by others. We derive ground-state scattering wave functions and analyze cold collisional properties of these systems for a wide range of energies. We find that, in order to get convergent results for the total scattering cross sections for energies of the order 1 K, one needs to take into account at least 60 partial waves. Low energy scattering properties calculated in this paper may serve as a precursor for experimental exploration of quantum collisions between an alkali atom and an alkali ion of different nucleus.

physics.atom-ph↗
arXiv2015

A model study on atom-atom interactions with large scattering length in quasi-two dimensional traps

We carry out a model study on two-atom interactions and bound states in quasi-two dimensional traps. The interactions are modeled by two-parameter potentials with parameters being the range $r_0$ and the $s$-wave scattering length $a_s$. We show that one can make use of two forms of finite-range model potentials, one for $a_s > 0$ and the other for $a_s < 0$. Both potentials reduce to same form in the limits $a_s \rightarrow \pm \infty $. We investigate into the dependence of the binding energies and the wave functions of two-atom trap-bound states on $a_s$ and $r_0$. In particular, we study the effects of $a_s$ ranging from large negative to large positive values on the bound state properties. Our results show that long-range interactions with infinite scattering length significantly alter the ground-state energy of the two atoms in a quasi-two or two dimensional trap. In contrast, short-range interactions can not significantly change the ground-state energy of two atoms in a 2D harmonic trap.

physics.atom-ph↗
arXiv2014

Optical Feshbach resonances through a molecular dark state: Efficient manipulation of $p$-wave resonances in fermionic $^{171}$Yb atoms

In a recent experiment by Yamazaki {\it et al.} [Phys.Rev. A {\bf 87} 010704 (R) (2013) ], $p$-wave optical Feshbach resonance in fermionic $^{171}$Yb atoms using purely long-range molecular excited states has been demonstrated. We theoretically show that, if two purely long range excited states of $^{171}$Yb are coupled to the ground-state continuum of scattering states with two lasers, then it is possible to significantly suppress photoassociative atom loss by a dark resonance in the excited states. We present a general theoretical framework for creating a dark state in electronically excited molecular potential for the purpose of increasing the efficiency of an optical Feshbach resonance. This can be accomplished by properly adjusting the relative intensity, phase, polarizations and frequency detunings of two lasers. We present selective numerical results on atom loss spectra, $p$-wave elastic and inelastic scattering cross sections of $^{171}$Yb atoms to illustrate the effects of the molecular dark state on optical Feshbach resonance.

physics.atom-ph↗
arXiv2014

Decay dynamics in a strongly driven atom-molecule coupled system

Within the framework of master equation, we study decay dynamics of an atom-molecule system strongly coupled by two photoassociation lasers. Summing over the infinite number of electromagnetic vacuum modes that are coupled to the laser-dressed atom-molecule system, we obtain an integro-differential master equation for the the system's reduced density matrix. The equation is numerically solved to describe system dynamics in the presence of decay. In particular, we discuss correlated spontaneous emission from a pair of electronically excited diatomic ro-vibrational states due to their laser induced coupling to the ground continuum of atomic scattering states. This allows us to calculate time-dependence of emitted radiation intensity. It exhibits quantum beats due to coherent dynamics. The phase difference between the two driving fields is found to significantly affect the decay dynamics and the beats. Our results demonstrate the possibility to control decay from the molecular excited states and the decoherence between them by changing the relative intensity and the phase between the lasers. We further show that, if the ground-state continuum has a shape resonance at a low energy, then the quantum beats show two distinctive time scales of oscillations in the strong coupling regime. One of the time scales originates from the energy gap between the two excited states while the other time scale corresponds to the collision energy at which free-bound Franck-Condon overlap is resonantly peaked due to the shape resonance.

physics.atom-ph↗
arXiv2012

Vacuum-Induced Coherence in Ultracold Photoassociative Ro-Vibrational Excitations

We show that coherence between two excited ro-vibrational states belonging to the same molecular electronic configuration arises quite naturally due to their interaction with electromagnetic vacuum. For initial preparation of a molecule in the desired ro-vibrational states, we propose to employ the method of ultracold photoassociation. Spontaneous decay of the excited molecule then gives rise to vacuum induced coherence between the excited ro-vibrational states. We demonstrate theoretically an interesting interplay of effects due to vacuum induced coherence and photoassociation. We apply our theory to photoassociation of bosonic Ytterbium (^{174}Yb) atoms which appear to be a promising system for exploring such interplay. The effects discussed here can be important for controlling decoherence and dissipation in molecular systems.

physics.atom-ph↗
arXiv2009

Suppression of power-broadening in strong-coupling photoassociation in the presence of a Feshbach resonance

Photoassociation (PA) spectrum in the presence of a magnetic Feshbach resonance is analyzed. Nonperturbative solution of the problem yields analytical expressions for PA linewidth and shift which are applicable for arbitrary PA laser intensity and magnetic field tuning of Feshbach Resonance. We show that by tuning magnetic field close to Fano minimum, it is possible to suppress power broadening at increased laser intensities. This occurs due to quantum interference of PA transitions from unperturbed and perturbed continuum. Line narrowing at high laser intensities is accompanied by large spectral shifts. We briefly discuss important consequences of line narrowing in cold collisions.

physics.atom-ph↗