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arXiv:2211.06000 · Physical Review A

Direction-dependent coupling between a nanofiber-guided light field and a two-level atom with an electric quadrupole transition

Fam Le Kien, Síle Nic Chormaic, Thomas Busch

Published Jan 19, 2023• 4 citations
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Abstract

We study the directional dependence of the coupling between a nanofiber-guided light field and a two-level atom with an electric quadrupole transition. We examine the situation where the nanofiber is aligned along the $z$ axis, the atom lies on the fiber transverse $x$ axis, the quantization axis for the atomic internal states is the other orthogonal transverse $y$ axis, the atomic upper and lower levels are the magnetic sublevels ${M}^{\ensuremath{'}}$ and $M$ of hyperfine-structure levels of an alkali-metal atom, and the field is in a quasilinearly polarized fundamental guided mode ${\mathrm{HE}}_{11}$ with the polarization $\ensuremath{\xi}=x$ or $y$. We find that the absolute value of the quadrupole Rabi frequency depends on the propagation direction of the light field in the cases of (${M}^{\ensuremath{'}}\ensuremath{-}M=\ifmmode\pm\else\textpm\fi{}1, \ensuremath{\xi}=y$) and (${M}^{\ensuremath{'}}\ensuremath{-}M=\ifmmode\pm\else\textpm\fi{}2, \ensuremath{\xi}=x$). We show that the directional dependence of the coupling leads to the directional dependence of spontaneous emission into guided modes. We find that the directional dependence of the atom-field coupling in the case of quadrupole transitions is not entirely due to spin-orbit coupling of light: there are some other contributions resulting from the gradient of the spatial phase factor of the field.

DOI
10.1103/physreva.107.013713

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