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Bimalendu Deb

Publications and source records attributed to Bimalendu Deb.

At least 73 records · Page 4Linked to original sources
arXiv2012

Resonant Manipulation of d-wave Interaction of Cold Atoms with Two Lasers and a Magnetic Field

We present a theory for manipulation of d-wave interaction of cold atoms with two lasers strongly driving two photoassociative transitions. The theory predicts the occurrence of a coherence between two excited ro-vibrational bound states due to the photoassociative dipole-couplings of ground-state d-wave scattering state to the bound states. We show that this excited-state coherence significantly influences atom-atom interaction. In particular, this leads to the enhancement of d-wave elastic scattering and to the suppression of inelastic scattering. In the presence of an s-wave magnetic Feshbach resonance, the two lasers can couple the s-wave resonance with the d-wave scattering state leading to the further enhancement in d-wave scattering at relatively low energy. Our numerical calculations based on realistic parameters show that d-wave manipulation would be most effective in case of atoms having excited diatomic states with narrow natural linewidth. We estimate that at 100 $μ$K the inelastic scattering rate in Yb can be reduced to 20 s$^{-1}$ while the elastic scattering rate can be two orders of magnitude larger.

cond-mat.quant-gas↗
arXiv2012

Electric field induced saturation effects in photoassociation of a pair of heteronuclear atoms

We theoretically study saturation effects induced by an external static electric field on photoassociation (PA) of a heteronuclear atom pair. A static electric field influences scattering wave-function of two heteronuclear atoms as described in [D. Chakraborty, J. Hazra and B. Deb, J. Phys. B. {\bf 44} 095201 (2011)]. For certain values of electric field strengths there exist anisotropic resonances in ground state scattering leading to a large modification of scattering wave-function at short and intermediate separations where photoassociative Franck-Condon overlap is significant. Photoassociation rate as a function of collision energy shows a splitting near resonant electric field in the mili Kelvin energy regime. This splitting with a prominent dip occurs due to resonant enhancement of free-bound stimulated linewidth leading to saturation in free-bound transitions. We study electric field induced saturation effects on both one- and two-colour PA. Our results suggest that a static electric field may influence the formation of ground state polar molecules in two-colour PA.

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↗
arXiv2011

Resonant enhancement of ultracold photoassociation rate by electric field induced anisotropic interaction

We study the effects of a static electric field on the photoassociation of a heteronuclear atom-pair into a polar molecule. The interaction of permanent dipole moment with a static electric field largely affects the ground state continuum wave function of the atom-pair at short separations where photoassociation transitions occur according to Franck-Condon principle. Electric field induced anisotropic interaction between two heteronuclear ground state atoms leads to scattering resonances at some specific electric fields. Near such resonances the amplitude of scattering wave function at short separation increases by several orders of magnitude. As a result, photoaasociation rate is enhanced by several orders of magnitude near the resonances. We discuss in detail electric field modified atom-atom scattering properties and resonances. We calculate photoassociation rate that shows giant enhancement due to electric field tunable anisotropic resonances. We present selected results among which particularly important are the excitations of higher rotational levels in ultracold photoassociation due to electric field tunable resonances.

physics.atom-ph↗
arXiv2010

Magneto-optical Feshbach resonance: Controlling cold collision with quantum interference

We propose a method of controlling two-atom interaction using both magnetic and laser fields. We analyse the role of quantum interference between magnetic and optical Feshbach resonances in controlling cold collision. In particular, we demonstrate that this method allows us to suppress inelastic and enhance elastic scattering cross sections. Quantum interference is shown to modify significantly the threshold behaviour and resonant interaction of ultracold atoms. Furthermore, we show that it is possible to manipulate not only the spherically symmetric s-wave interaction but also the anisotropic higher partial-wave interactions which are particularly important for high temperature superfluid or superconducting phases of matter.

physics.atom-ph↗
arXiv2009

Rotational excitations in two-color photoassociation

We show that it is possible to excite higher rotational states J > 2 in ultracold photoassociation by two laser fields. Usually higher J states are suppressed in photoassociation at ultracold temperatures in the regime of Wigner threshold laws. We propose a scheme in which one strong laser field drives photoassociation transition close to either J = 1 or J = 2 rotational state of a particular vibrational level of an electronically excited molecule. The other laser field is tuned near photoassociation resonance with J > 2 rotational levels of the same vibrational state. The strong laser field induces a strong continnum-bound dipole coupling. The resulting dipole force between two colliding atoms modifies the continnum states forming continnum-bound dressed states with a significant component of higher partial waves in the continnum configuration. When the second laser is scanned near the resonance of the higher J states, these states become populated due to photoassociative transitions from the modified continnum.

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↗
arXiv2009

Feshbach Resonance Induced Fano Interference in Photoassociation

We consider photoassociation from a state of two free atoms when the continuum state is close to a magnetic field induced Feshbach resonance and analyze Fano interference in photoassociation. We show that the minimum in photoassociation profiles characterized by the Fano asymmetry parameter $q$ is independent of laser intensity, while the maximum explicitly depends on laser intensity. We further discuss the possibility of nonlinear Fano effect in photoassociation near a Feshbach resonance.

physics.atom-ph↗
arXiv2007

Finite temperature effects in light scattering off Cooper-paired Fermi atoms

We study stimulated light scattering off a superfluid Fermi gas of atoms at finite temperature. We derive response function that takes into account vertex correction due to final state interactions; and analyze finite temperature effects on collective and quasiparticle excitations of a uniform superfluid Fermi gas. Light polarization is shown to play an important role in excitations. Our results suggest that it is possible to excite Bogoliubov-Anderson phonon at a large scattering length by light scattering.

cond-mat.other↗
arXiv2006

Pair-correlation in Bose-Einstein Condensate and Fermi Superfluid of Atomic Gases

We describe pair-correlation inherent in the structure of many-particle ground state of quantum gases, namely, Bose Einstein condensate and Cooper-paired Fermi superfluid of atomic gases. We make a comparative study on the pair-correlation properties of these two systems. We discuss how to probe this pair-correlation by stimulated light scattering. This intrinsic pair-correlation may serve as a resource for many-particle entanglement.

cond-mat.supr-con↗
arXiv2005

Light scattering in Cooper-paired Fermi atoms

We present a detailed theoretical study of light scattering off superfluid trapped Fermi gas of atoms at zero temperature. We apply Nambu-Gorkov formalism of superconductivity to calculate the response function of superfluid gas due to stimulated light scattering taking into account the final state interactions. The polarization of light has been shown to play a significant role in response of Cooper-pairs in the presence of a magnetic field. Particularly important is a scheme of polarization-selective light scattering by either spin-component of the Cooper-pairs leading to the single-particle excitations of one spin-component only. These excitations have a threshold of $2Δ$ where $Δ$ is the superfluid gap energy. Furthermore, polarization-selective light scattering allows for unequal energy and momentum transfer to the two partner atoms of a Cooper-pair. In the regime of low energy ($<< 2Δ$) and low momentum ($<2Δ/(\hbar v_F)$, $v_F$ being the Fermi velocity) transfer, a small difference in momentum transfers to the two spin-components may be useful in exciting Bogoliubov-Anderson phonon mode. We present detailed results on the dynamic structure factor (DSF) deduced from the response function making use of generalized fluctuation-dissipation theorem. Model calculations using local density approximation for trapped superfluid Fermi gas shows that when the energy transfer is less than $2Δ_0$, where $Δ_0$ refers to the gap at the trap center, DSF as a function of energy transfer has reduced gradient compared to that of normal Fermi gas.

cond-mat.other↗
arXiv2005

Probing pairing gap in Fermi atoms by light scattering

We study stimulated scattering of polarized light in a two-component Fermi gas of atoms at zero temperature. Within the framework of Nambu-Gorkov formalism, we calculate the response function of superfluid gas taking into account the final state interactions. The dynamic structure factor deduced from the response function provides information about the pairing gap and the momentum distributions of atoms. Model calculations using local density approximation indicates that the pairing gap of trapped Fermi gas may be detectable by Bragg spectroscopy due to stimulated scattering.

cond-mat.other↗
arXiv2004

Interior gap superfluidity in a two-component Fermi gas of atoms

A new superfluid phase in Fermi matter, termed as "interior gap" (IG) or "breached pair", has been recently predicted by Liu and Wilczek [Phys.Rev.Lett. {\bf 90}, 047002 (2003)]. This results from pairing between fermions of two species having essentially different Fermi surfaces. Using a nonperturbative variational approach, we analyze the features, such as energy gap, momentum distributions, and elementary excitations associated with the predicted phase. We discuss possible realization of this phase in two-component Fermi gases in an optical trap.

cond-mat.other↗
arXiv2004

Bragg scattering of light in a strongly interacting trapped Fermi gas of atoms

We study Bragg scattering of laser light by trapped Fermi atoms having two hyperfine spin components in the unitarity-limited strongly interacting regime at zero temperature. We calculate the dynamic structure function of the superfluid trapped Fermi gas in the unitarity limit. Model calculation using local density approximation shows that, the superfluid pairing gap in the unitarity limit is detectable from the measurements of dynamic structure function by Bragg spectroscopy, while in the weak-coupling BCS limit, the gap eludes such spectroscopic detection.

cond-mat.supr-con↗
arXiv2001

Laser-Induced Entangled Giant Quasi-Molecules in Optical Lattices

We analyze atom-atom interactions in optical lattices due to a laser-induced long-range interatomic force which prevails over the usual London-van der-Waals forces. This force, which can be generated by an intense laser field at a wavelength longer than that of the lattice-generating laser, is shown to bind pairs of cold atoms trapped at different lattice sites, and cause their translational quantum correlations (spatial entanglement).

quant-ph↗