Abstract
We present a novel approach for the optical manipulation of neutral atoms in annular light structures produced by the phenomenon of conical refraction occurring in biaxial optical crystals. For a beam focused to a plane behind the crystal, the focal plane exhibits two concentric bright rings enclosing a ring of null intensity called the Poggendorff ring. We demonstrate both theoretically and experimentally that the Poggendorff dark ring of conical refraction is confined in three dimensions by regions of higher intensity. We derive the positions of the confining intensity maxima and minima and discuss the application of the Poggendorff ring for trapping ultra-cold atoms using the repulsive dipole force of blue-detuned light. We give analytical expressions for the trapping frequencies and potential depths along both the radial and the axial directions. Finally, we present realistic numerical simulations of the dynamics of a 87Rb Bose-Einstein condensate trapped inside the Poggendorff ring which are in good agreement with corresponding experimental results.
Highlights
Optical ring potentials (ORPs) with axial symmetry are considered as basic building blocks and the simplest nontrivial closed-loop circuits in atomtronics [1,2,3,4,5] and atom interferometry [6]
We have presented a novel approach for generating toroidal optical traps for ultracold neutral atoms by applying the Poggendorff dark ring (PDR) as a blue-detuned toroidal trap for Bose-Einstein condensates (BECs) We have studied the normalized intensity distribution around the annular ring structure of the conical refraction (CR) phenomenon in biaxial crystals
For a well developed CR ring, i.e. when R0 w0, experimental results of the intensity distribution are compared with the exact paraxial solution and with its asymptotic approximation
Summary
Optical ring potentials (ORPs) with axial symmetry are considered as basic building blocks and the simplest nontrivial closed-loop circuits in atomtronics [1,2,3,4,5] and atom interferometry [6]. Blue-detuned ORPs have been experimentally reported by means of LG beams generated with spatial light modulators (SLMs) [22] and by amplitude masks [23,24,25] These two techniques might experience the following limita-. We discuss the use of the PDR as a blue-detuned ORP for ultra-cold atoms and demonstrate this with a 87Rb BEC This technique has the advantage of the easy generation of the toroidal dark trap, which only needs a focused Gaussian beam and a biaxial crystal. CR provides the full conversion of the input power into the toroidal dark trap, in contrast to the previously reported methods which introduce losses due to diffraction in the generation of LG beams These features make the CR toroidal dark-focus beam very attractive for particle [34] and atom [10, 11, 19] trapping, in particular with blue-detuned light beams [9].
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