Enhanced Quadrupole Effects for Atoms in Optical Vortices

We show that the normally weak optical quadrupole interaction in atoms is enhanced significantly when the atom interacts at near resonance with an optical vortex. In particular, the forces and torque acting on the atom are shown here to scale up with the square of the winding number $l$ of the vortex. Because the integer $l$ can be arranged to be large, this property allows for processes involving dipole-forbidden, but quadrupole-allowed, transitions in atoms, such as cesium and oxygen, to come into play. We show that the mechanical effects of vortex light on atoms involving translational and rotational motion as well as trapping should be significantly enhanced for quadrupole transitions and present novel features with useful implications for the emerging field of atomtronics.

Figure 1

(a) The modulus squared Rabi frequency $|{\Omega }_{klp}^Q(\mathbf{R}){|}^2$, in units of ${\Omega }_0^2$ defined in Eq. (26) for an atom in a Laguerre-Gaussian doughnut mode for which $l=1$, $p=0$. Distances are in units of $w_0$. (b) The large $l$ case, $l=300$, $p=0$. The inset in each case shows the projections in the $X\mathrm{\text{−}}Y$ plane. The color code is such that from magenta to red is equivalent to from minimum to maximum. See the text for the parameters used to generate these figures and a discussion of the main features. The gray-scale color code is such that from dark gray (magenta) to light gray (red) is equivalent to from minimum to maximum.

Figure 2

The quadrupole optical potential distribution in millidegrees Kelvin (mK) for a doughnut mode with large $l$ where $l=300$, $p=0$. The color code is the same as in Fig. 1; magenta now represents the lowest negative values of the quadrupolar trapping potential. The inset shows the projection in the $X\mathrm{\text{−}}Y$ plane. See the text for the parameters used to generate this plot and a discussion of the main features. The gray-scale color code is such that from dark gray (magenta) to light gray (red) is equivalent to from minimum to maximum.