Bose-Einstein condensates (BECs) provide the opportunity to study the rotational properties of quantum fluids in a low density regime. Early experiments created scalar vortices in single-component BECs, and showed that they share many of the characteristics of denser superfluids such as quantized angular momentum and persistent current.
Vortices have also been created in multi-component, or spinor, BECs, in which case the wave function, or macroscopic order parameter, of the condensate is a vector. A vortex in one of the components of a spinor BEC is equivalent to a scalar vortex in a single-component condensate; the vortex core, however, can be filled with atoms in one of the other populated spin states, leaving the overall density of the cloud non-singular.
''Coreless'' vortices can be coherently created by transferring orbital angular momentum from a Laguerre-Gaussian (LG) beam to the condensate through the use of a two-photon Raman technique. This coherent population transfer interaction, along with the fundamental differences between the rotational properties of scalar and coreless vortices are discussed, and analysis is presented on several specific spin textures including two and three-component coreless vortices created in either a spin-1 or spin-2 87Rb BEC. The rotation of the vortices is confirmed directly through matter-wave interference.
The coreless vortex creation process can be interpreted as the coherent transfer of optical information from the LG beam to matter: the two-photon Raman interaction in a lambda configuration writes the difference in the electric fields into the vectorial wave function of the spinor BEC. This process simultaneously transfers population between the initial and final states of the lambda system, creating a ground state coherence between the populated states.
If the two Raman beams are a defocused Gaussian and a tightly focused LG beam, then the doughnut intensity profile and the azimuthal phase winding of the LG beam is written into the condensate in the form of a two-component coreless vortex. This optical information can then be retrieved from the BEC through the application of a uniform intensity ''read'' beam to one transition of the lambda system. The interaction between this read beam and the ground state coherence generates light on the other transition of the lambda with an intensity profile and phase corresponding to the initial LG beam.
A model is presented that uses the density matrix formalism to describe this transfer and retrieval of optical information in all three spatial dimensions as well as time. The dependence of the intensity profile, phase, and total energy of the generated light is investigated as function of the intensity and single-photon detuning of the read beam for both the case of a homogeneous BEC and one with a Gaussian density distribution.
|Advisor:||Bigelow, Nicholas P.|
|Commitee:||Alonso, Miguel A., Jordan, Andrew N., Novotny, Lukas, Tang, Ching W.|
|School:||University of Rochester|
|Department:||Hajim School of Engineering and Applied Sciences|
|School Location:||United States -- New York|
|Source:||DAI-B 74/03(E), Dissertation Abstracts International|
|Subjects:||Physics, Theoretical physics|
|Keywords:||Bose-Einstein condensate, Coreless vortices, Quantum fluids, Spinors|
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