State Research Center OPTIMAS

Magic Wavelength of Rubidium

“Tug of War” for the magic wavelength. At a wavelength of 790 nano meter, strong counteracting light forces influence the atomic Rubidium. The precise position of the magic wavelength, where the counteracting forces add to zero, strongly depends on normally negligible forces (red) due to light polarization and inner electron shells. Therefore, by precisely measuring the zero-crossing, these components can be identified and characterized. (Fig. adapted from cliparts.co)

So-called magic wavelengths find extensive usage in atomic physics applications, ranging from spectroscopy and metrology to the engineering of state- and species-dependent traps for ultracold quantum gases. Besides, these systems serve as excellent test beds for atomic structure investigations beyond standard two level treatments. In an experimental study of such a magic wavelength in ultracold Rubidium, a tug of war of light forces acting on the atoms was realized that enabled the scientists to investigate normally negligible light force contributions.

Usually, the atom's electronic structure is investigated by observing the change of color, or technically speaking the wavelength of light interacting with the atom. However, this interplay is not a one-way road. When irrading the atom with a laser, the light bends the electronic structure, and exerts a force on the atom. In this particular case, the OPTIMAS scientists have investigated the interaction of a Rubidium Bose-Einstein condensate with a laser at the magic wavelength of 790 nano meter, where the light attracts and repells Rubidium simultaneously creating a situation where strong opposing forces cancel.

In this high-precision measurement the influence of circular light polarization and inner electron shells to tip the scale of the total force was identified, although being three orders of magnitude smaller than the dominant players. While the former can be exploited for an application in experiments similar to the one presented here, the latter helps to stiffen a more comprehensive picture of basic light-matter interaction.

The study by the research group of OPTIMAS-member Artur Widera was recently:
Felix Schmidt, Daniel Mayer, Michael Hohmann, Tobias Lausch, Farina Kindermann, and Artur Widera:
Precision measurement of the 87Rb tune-out wavelength in the hyperfine ground state F = 1 at 790 nm
PHYSICAL REVIEW A 93, 022507 (2016)
http://link.aps.org/doi/10.1103/PhysRevA.93.022507

“Tug of War” for the magic wavelength. At a wavelength of 790 nano meter, strong counteracting light forces influence the atomic Rubidium. The precise position of the magic wavelength, where the counteracting forces add to zero, strongly depends on normally negligible forces (red) due to light polarization and inner electron shells. Therefore, by precisely measuring the zero-crossing, these components can be identified and characterized. (Fig. adapted from cliparts.co)