Bimalendu Deb

Low voltage electrodeposition of diamond-like carbon films

Abstract Diamond-like carbon (DLC) films were deposited by electrodeposition technique onto SnO 2 -coated glass substrates by using a mixture of acetic acid and water as electrolyte. The applied voltage between the electrodes was mere 2.1 V. The films have rough surface and distinct broad characteristic peaks at ∼1336 and ∼1601 cm −1 dominated the Raman spectra. Band gap and refractive index of the films varied between 2.3–2.65 eV and 1.25–1.3, respectively. Photoluminscence studies indicate excitonic transition at ∼2.62 eV.

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 analyse 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 the nonlinear Fano effect in photoassociation near a Feshbach resonance.

Ion-atom cold collision: Formation of cold molecular ion by radiative processes

Molecular ions are important for a variety of fundamental studies in physics. For instance, it is proposed that cold molecular ions would be useful for measuring electron dipole moment (EDM) [1, 2]. Study of cold molecular ions has relevance in diverse areas such as metrology [3, 4] and astrochemistry [5]. Recently, molecular ions are cooled into ro-vibrational ground states by all optical [6], laser and sympathetic cooling methods [7, 8]. A large variety of diatomic and triatomic molecular ions are also cooled by sympathetic method [9–11]. Other methods such as photoassociative ionisation [12–16], buffer gas [17], and rotational cooling [18] have been widely used for producing low energy molecular ions. Since cooling of neutral atoms and atomic ions down to sub-milliKelvin temperature regime is possible with currently available technology of laser cooling, it is now natural to ask ourselves: Is it possible to form cold molecular ion by atom-ion cold collision? Recent progress in developing hybrid traps [19–22] where both atomic ions and neutral atoms can be simultaneously confined provides new opportunity for exploring ion-atom quantum dynamics and charge transfer reactions at ultralow

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

The photoassociation (PA) spectrum is analysed in the presence of a magnetic Feshbach resonance. A 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 the magnetic field close to the 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 the important consequences of line narrowing in cold collisions.

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.

Manipulating Higher Partial-Wave Atom-Atom Interactions by Strong Photoassociative Coupling

We show that it is possible to change not only s-wave but also higher partial-wave atom-atom interactions in a cold collision in the presence of relatively intense laser fields tuned near a photoassociative transition.

Resonant enhancement of the ultracold photoassociation rate by an 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.

Creation and manipulation of bound states in the continuum with lasers: Applications to cold atoms and molecules

We show theoretically that it is possible to create and manipulate a pair of bound states in continuum in ultracold atoms by two lasers in the presence of a magnetically tunable Feshbach resonance. These bound states are formed due to coherent superposition of two electronically excited molecular bound states and a quasi-bound state in ground-state potential. These superposition states are decoupled from the continuum of two-atom collisional states. Hence, in the absence of other damping processes they are non-decaying. We analyze in detail the physical conditions that can lead to the formation of such states in cold collisions between atoms, and discuss the possible experimental signatures of such states. An extremely narrow and asymmetric shape with a distinct minimum of photoassociative absorption spectrum or scattering cross section as a function of collision energy will indicate the occurrence of a bound state in continuum (BIC). We prove that the minimum will occur at an energy at which the BIC is formed. We discuss how a BIC will be useful for efficient creation of Feshbach molecules and manipulation of cold collisions. Experimental realizations of BIC will pave the way for a new kind of bound-bound spectroscopy in ultracold atoms.

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

We study theoretically interaction potentials and low-energy collisions between different alkali atoms and alkali ions. Specifically, we consider systems such as X + , where X( 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 a pseudopotential method and compare our results with those obtained by others. We derive ground-state scattering wave functions and analyze the 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. The 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 a different nucleus.

Entangling two Bose-Einstein condensates by stimulated Bragg scattering

We propose an experiment for entangling two spatially separated Bose-Einstein condensates by Bragg scattering of light. When Bragg scattering in two condensates is stimulated by a common probe, the resulting quasiparticles or particles in the two condensates get entangled due to quantum communication between the condensates via the probe beam. The entanglement is shown to be significant and occurs in both number and quadrature phase variables and depends strongly on the relative detuning of the two pumps and the relative atom-field coupling strengths of the two condensates. We present two methods of detecting the generated entanglement.