Atom vortex beams

The concept that all de Broglie particles can form vortex beams is analyzed for neutral atoms. It is shown how atoms diffracted from a suitably constructed optical mask configuration employing light of $l$ units of orbital angular momentum and at far-off resonance with an atomic transition can lead to the generation of a discrete set of atom vortex beams each endowed with the property of quantized orbital angular momentum about the beam axis in units of $\hslash l$. Selection criteria of atom vortex beams are derived and the functioning of the mask configuration for angular dispersion of beams in terms of de Broglie wavelength is analyzed. Prospects of applications in the areas of atom interferometry and dispersion, and quantum information processing via atom vortices are pointed out.

Figure 1

(a) Schematic representation of the diffraction of the atoms through the light mask made up of a Laguerre-Gaussian doughnut beam of winding number $l$ interfering with a tilted plane wave $l=2$; (b) after the diffraction process the different atom vortices are shown separated in space and are labeled $n=0,\pm 1\pm 2,...$ with the $n$th vortex carrying orbital angular momentum $nl\hslash$.

Figure 2

The forklike light mask displaying the intensity of the field given by Eq. (1), for a winding number $l=1$. Lighter gray areas correspond to higher intensity.