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arXiv:1906.01968

Dynamics of the creation of a rotating Bose-Einstein condensate by two-photon Raman transition using Laguerre-Gaussian pulse

K. Mukherjee, Soumik Bandyopadhyay, D. Angom, A. Martin, Sonjoy Majumder

Published Jun 3, 2019• 0 citations
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Abstract

We examine the dynamics associated with the creation of a vortex in a Bose-Einstein condensate (BEC), from another nonrotating BEC using two-photon Raman transition with Gaussian (G) and Laguerre-Gaussian (LG) laser pulses. In particular, we consider BEC of Rb atoms at their hyperfine ground states confined in a quasi two dimensional harmonic trap. Optical dipole potentials created by G and LG laser pulses modify the harmonic trap in such a way that density profiles of the condensates during the Raman transition process depend on the sign of the generated vortex. We investigate the role played by the Raman coupling parameter manifested through dimensionless peak Rabi frequency and intercomponent interaction on the dynamics of the population transfer process and on the final population of the rotating condensate. During the Raman transition process, the two BECs tend to have larger overlap with each other for stronger intercomponent interaction strength.

DOI
10.48550/arxiv.1906.01968

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We present numerical simulations to unravel the dynamics associated with the creation of a vortex in a Bose–Einstein condensate (BEC), from another nonrotating BEC using two-photon Raman transition with Gaussian (G) and Laguerre–Gaussian (LG) laser pulses. In particular, we consider BEC of Rb atoms at their hyperfine ground states confined in a quasi two dimensional harmonic trap. Optical dipole potentials created by G and LG laser pulses modify the harmonic trap in such a way that density patterns of the condensates during the Raman transition process depend on the sign of the generated vortex. We investigate the role played by the Raman coupling parameter manifested through dimensionless peak Rabi frequency and intercomponent interaction on the dynamics during the population transfer process and on the final population of the rotating condensate. During the Raman transition process, the two BECs tend to have larger overlap with each other for stronger intercomponent interaction strength.
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The density profiles of two component Bose-Einstein condensate (BEC) are studied across the trap using the microscopic interaction with Laguerre-Gaussian (LG) beam. We consider 87^{87}87Rb BEC in two hyperfine spin states as components and the wavelength of the LG beam is comparable to the atomic de-Broglie wavelength. Competitions between intra- and inter-component interactions produce interesting density structures of the ground state of BEC. Properties of the BEC components are realized from the estimation of the Rabi frequency of two photon stimulated Raman transition over the inter-coupling strengths. We demonstrate interference of vortex-antivortex in terms of inter-component interactions when both the components are subjected to appropriate Raman transitions.
A coherent coupler is proposed to spin a Bose-Einstein condensate composed of ultracold alkali atoms into a vortex state. The proposal is based on a Raman transition induced by two copropagating ${\ensuremath{\sigma}}^{+}$ and ${\ensuremath{\sigma}}^{\ensuremath{-}}$ polarized Laguerre-Gaussian laser beams with different frequencies. We show that the transfer of angular momentum of photons to the condensed atoms through a Raman transition leads to a coherent coupling of the ground-state condensate to a rotating condensate in a vortex state. The detection of such a vortex state is discussed.
We demonstrate the coherent transfer of the orbital angular momentum of a photon to an atom in quantized units of h, using a 2-photon stimulated Raman process with Laguerre-Gaussian beams to generate an atomic vortex state in a Bose-Einstein condensate of sodium atoms. We show that the process is coherent by creating superpositions of different vortex states, where the relative phase between the states is determined by the relative phases of the optical fields. Furthermore, we create vortices of charge 2 by transferring to each atom the orbital angular momentum of two photons. We subsequently use our technique to induce rotation of the condensate confined in an asymmetric, ring-shaped hybrid optical and magnetic trap. We observe the cloud rotating for up to 13 seconds, due to the superfluid character of the condensate.
We present the theory of microscopic interaction of the spin-orbit coupled focused Laguerre-Gaussian beam with the two-component Bose–Einstein condensate , composed of two hyperfine states of 87 Rb in a harmonic trap. We have shown that Raman Rabi frequency distributions over the inter-component coupling identify phase separation coupling strength. A significant enhancement of side-band transitions due to non-paraxial nature of vortex beam is observed for particular values of inter-component coupling around 1.25 and 0.64 in unit of 5.5 nm for 10 5 and 10 6 number of atoms, respectively. The uncertainty in the estimation of these coupling strengths is improved with the focusing angles of the beam. We discuss an experimental scheme to verify this non-paraxial effect on ultra-cold atoms.