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Observation of mechanical Faraday effect in gas media

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 Added by Valery Milner
 Publication date 2021
  fields Physics
and research's language is English




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We report the experimental observation of the rotation of the polarization plane of light propagating in a gas of fast-spinning molecules (molecular super-rotors). In the observed effect, related to Fermis prediction of polarization drag by a rotating medium, the vector of linear polarization tilts in the direction of molecular rotation due to the rotation-induced difference in the refractive indices for the left and right circularly polarized components. We use an optical centrifuge to bring the molecules in a gas sample to ultrafast unidirectional rotation and measure the polarization drag angles of the order of 0.2 milliradians in a number of gases under ambient conditions. We demonstrate an all-optical control of the drag magnitude and direction, and investigate the robustness of the mechanical Faraday effect with respect to molecular collisions.



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It is proposed to employ the P,T-odd Faraday effect, i.e. rotation of the polarization plane of the light propagating through a medium in presence of the electric field, as a tool for observation of P,T-odd effects caused by CP violation within the Standard Model. For this purpose the vapors of heavy atoms like Tl, Pb, Bi are most suitable. Estimates within the Standard Model show: provided that applied field is about 10^5 V/cm and the optical length can be as large as 70000 km, the rotation angle may reach the value corresponding to the recently observable values (10^{-9} rad). These estimates demonstrate that the P,T-odd Faraday effect observations may effectively compete with the recent measurements of the electron spin rotation in an external electric field, performed with diatomic molecules. These measurements exclude the P,T-odd effects at the level 9 orders of magnitude higher than the predictions of the Standard Model.
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Accurate evaluation of the $mathcal{P}$,$mathcal{T}$-odd Faraday effect (rotation of the polarization plane for the light propagating through a medium in presence of an external electric field) is presented. This effect can arise only due to the $mathcal{P}$,$mathcal{T}$-odd interactions and is different from the ordinary Faraday effect, i.e. the light polarization plane rotation in an external magnetic field. The rotation angle is evaluated for the ICAS (intracavity absorption spectroscopy) type experiments with Xe and Hg atoms. The results show that Hg atom may become a good candidate for a search for the $mathcal{P}$,$mathcal{T}$-odd effects in atomic physics.
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