arXiv subjects

Somnath Naskar

Publications and source records attributed to Somnath Naskar.

6 recordsLinked to original sources

arXiv2020

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↗

arXiv2019

Suppressing deleterious effects of spontaneous emission in creating bound states in cold atom continuum

In a previous paper [B. Deb and G. S. Agarwal, Phys. Rev. A 90, 063417 (2014)], it was theoretically shown that, magneto-optical manipulation of low energy scattering resonances and atom-molecule transitions could lead to the formation of a bound state in continuum (BIC), provided there is no spontaneous emission. We find that even an exceedingly small spontaneous decay from exited molecular states can spoil the BIC. In this paper, we show how to circumvent the detrimental effect of spontaneous emission by making use of vacuum-induced coherence (VIC) which results in the cancellation or suppression of spontaneous emission. VIC occurs due to the destructive interference between two spontaneous decay pathways. An essential condition for VIC is the non-orthogonality of the transition dipole moments associated with the decays. Furthermore, the interference between decay pathways requires that the spacing between the two decaying states must be comparable to or smaller than the square root of the product of the two spontaneous linewidths. We demonstrate that these conditions can be fulfilled by microwave dressing of two appropriately chosen molecular excited states, opening a promising prospect for the experimental realization of BIC of cold atoms.

quant-ph↗

arXiv2018

Spectroscopic properties of the molecular ions BeX^+ (X=Na, K, Rb): Forming cold molecular ions from an ion-atom mixture by stimulated Raman adiabatic process

In this theoretical work, we calculate potential energy curves, spectroscopic pa- rameters and transition dipole moments of molecular ions BeX^+ (X=Na, K, Rb) composed of alkaline ion Be and alkali atom X with a quantum chemistry approach based on the pseudopotential model, Gaussian basis sets, effective core polarization potentials, and full configuration interaction (CI). We study in detail collisions of the alkaline ion and alkali atom in quantum regime. Besides, we study the possibility of the formation of molecular ions from the ion-atom colliding systems by stimu- lated Raman adiabatic process and discuss the parameters regime under which the population transfer is feasible. Our results are important for ion-atom cold collisions and experimental realization of cold molecular ion formation.

physics.atom-ph↗

arXiv2017

Optical cooling of interacting atoms in a tightly confined trap

In a recent paper, we have proposed a novel laser cooling scheme for reducing collisional energy of a pair of atoms by using photoassociative transitions. In that paper, we considered two atoms in free space, that is we have not considered the effects of trap on the cooling process. Here in this paper, we qualitatively discuss the possibility of extending this idea for Raman sideband cooling of a pair of interacting atoms trapped in Lamb-Dicke (LD) regime. Apart from cooling, our method may be important for manipulating on-site interaction of atoms in an optical lattice.

physics.atom-ph↗

arXiv2016

Formation of a molecular ion by photoassociative Raman processes

We show theoretically that it is possible to form a cold molecular ion from a pair of colliding atom and ion at low energy by photoassociative two-photon Raman processes. We explore the possibility of stimulated Raman adiabatic passage (STIRAP) from the continuum of ion-atom scattering states to an ionic molecular state. We provide physical conditions under which coherent population transfer is possible in stimulated Raman photoassociation. Our results are important for experimental realization of PA in ion-atom cold collisions.

physics.atom-ph↗

arXiv2016

Photoassociative cooling and trapping of a pair of interacting atoms

We show that it is possible to cool interacting pairs of atoms by a lin $\perp$ lin Sisyphus-like laser cooling scheme using counter-propagating photoassociation (PA) lasers. It is shown that the center-of-mass motion (c.m.) of atom pairs can be trapped in molecular spin-dependent periodic potentials generated by the lasers. The proposed scheme is most effective for narrow-line PA transitions. We illustrate this with numerical calculations using fermionic $^{171}$Yb atoms as an example.

physics.atm-clus↗