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Researchers successfully demonstrated a two-photon excitation of cesium-133 atoms near an optical nanofiber, observing the transition from ground state 6S₁/₂ to excited state 6D₅/₂ at exceptionally low power levels. The nanofiber's evanescent field enabled efficient excitation with only tens of microwatts, approximately 10,000 times less power than conventional free-space methods. The study revealed asymmetric spectral broadening with a red-shifted tail caused by surface-induced van der Waals interactions between atoms and the nanofiber.
Why it matters
This technique could enable more efficient quantum optics experiments and sensors by dramatically reducing the power requirements for nonlinear atomic processes. The findings advance understanding of atom-surface interactions in nanophotonic systems, which is crucial for developing compact quantum technologies and integrated optical devices.
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⚠️ Preprint – Noch nicht peer-reviewed
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Abstract: We report the experimental observation of the $^{text{133}}$Cs 6S$_{text{1/2}}$ to 6D$_{text{5/2}}$ single-frequency two-photon transition at low excitation power using an optical nanofiber embedded in a cold atom cloud. We investigate the 917 nm fluorescence spectra modified by the surface-induced interaction of the nanofiber, which exhibits a pronounced asymmetric broadening with a distinct red-shifted tail. We present a systematic theoretical description of the two-photon transition process of atoms near a nanofiber surface, considering atomic angular momentum coupling, guided-mode decay rate, and surface-induced van der Waals interactions. Owing to the tight spatial confinement provided by the guided evanescent field, efficient nonlinear excitation is realized at excitation powers down to tens of microwatts, corresponding to a reduction of approximately four orders of magnitude relative to typical free-space implementations. Our work reveals the interplay among waveguide-modified radiative dynamics, surface-induced interactions, and the spatial distribution of atoms around the nanofiber, and provides insights into further studies on nonlinear optical transitions and surface-mediated atomic dynamics in waveguide quantum electrodynamics systems.