In the recent years, the use of nanoscale waveguides providing tight transverse confinement of light has been pushed forward in the waveguide-QED field as a mean to enhance atom-photon interactions for large number of atoms. On our experiment, we use a two-color dipole trap scheme to interface cold Cesium atoms with the evanescent field of a tapered optical nanofiber. By tuning the properties of the dipole trap, we arrange the atoms in a 1D lattice geometry with controllable distance between them.
In the past, we used this platform to demonstrate an all-fibered optical memory at the single-photon level using dynamical EIT . We also investigated collective behaviors in such 1D chains of trapped atoms. We demonstrated up to 80\% Bragg reflection with as low as 2000 atoms when carefully tuning the interatomic distance . More recently, we heralded the creation of a single collective excitation in the atomic chain, which was subsequently stored and retrieved as a single photon in the guided mode of the nanofiber . We also theoretically studied the collective dynamics of cavity-QED-like atomic arrangements in both markovian and non-markovian regimes .
A strong motivation is also to reach quantum non-linearity at few-photon levels. In this context, controlling the propagation of a single photon with powers at the single-photon levels in cavity-free platforms has been studied in few systems , and still remains an important milestone for the community. Here, we report on guided optical switching and routing of single-photon level coherent fields using an atomic Bragg mirror controlled by very low energy fields. Focusing first on the regular three-level setup, we switch the reflection and the transmission paths of a Bragg mirror using electromagnetically-induced transparency (EIT). The control beam is guided and contains around few thousand photons. In order to push this number even lower, we employ a four-level scheme consisting of the previous scheme to which we add an additional level coupled with the metastable state by a switch field. We demonstrate optical switching with a switch field at the few-tens of photons level, thus reducing by one to two order of magnitude the number of photons needed. Routing, or controlled directionnality of the probe photon, is also achieved using the same four-level scheme with a switch field at at the few hundred photons level.
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 N. V. Corzo, B. Gouraud, A. Chandra, A. Goban, A. Sheremet, D. Kupriyanov, and J. Laurat, “Large bragg reflection from one-dimensional chains of trapped atoms near a nanoscale waveguide,” Phys. Rev. Lett. 117, 133603 (2016).
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 V. A. Pivovarov, L. V. Gerasimov, J. Berroir, T. Ray, J. Laurat, A. Urvoy, and D. V. Kupriyanov, “Single collective excitation of an atomic array trapped along a waveguide : a study of cooperative emission for different atomic chain configurations,” Phys. Rev. A 103, 043716 (2021).
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|Presenter name||Jérémy Berroir|
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