Trapping cold neutral atoms in close proximity to nanostructures has raised a large interest in recent years, pushing the frontiers of cavity-QED and boosting the emergence of the waveguide-QED field of research. Such platforms interfacing trapped cold atoms and guided light in nanoscale waveguides are a promising route to achieve a regime of strong coupling between light and atoms .
In this context, we propose to interface 87Rb atoms with a GaInP waveguide based on a 2D photonic crystal waveguide (PCW) . The periodic arangement of holes allows to shape the dispersion relation and engineer slow-modes , whose interaction with quantum emitters would be enhanced, allowing for strong coupling even in single pass. At the same time, guided modes are used to form dipole traps for the atoms, a crucial requirement for achieving strong coupling. The coupling of the atoms to the waveguide can be characterized by the Purcell factor, which relates the decay rate of the atoms into the guided mode to the one into free space. At realistic distances ∼ 100 nm from
the waveguide surface, FDTD calculations reveal that Purcell factors as high as 5 can be expected.
Moreover, dispersion engineering by tuning the geometrical parameters of the PCW can lead to a constant group index ng ∼ 30 over a range of 15 nm, centered around λRb,D2 = 780 nm, making the design more robust to fabrication imperfections. We introduce a stable trapping scheme around our PCW for 87Rb atoms based on an evanescent two-color dipole trap formed by fast guided modes.
This configuration was computed thanks to nanotrappy , a Python package developed by our group, to design, calculate and optimize dipole traps around nanoscale waveguides, making the search process faster and more systematic. Experimental realization of the cold atoms system is ongoing and promising first structures are being characterized.
 D. E. Chang, et al., Rev. Mod. Phys., 90, 031002 (2018)
 X. Zang, et al., Phys. Rev. Appl., 5, 024003 (2016)
 R. D. Meade, et al., Photonic crystals: Molding the flow of light (2008)
 J. Berroir, A. Bouscal, et al., Phys. Rev. Research, 4, 013079 (2022)
|Presenter name||Adrien Bouscal|
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