Atom-atom interactions around the band edge of a photonic crystal waveguide

In recent years, there has been considerable effort to bring ultracold atoms into the realm of nanophotonics. Nanoscopic dielectric devices offer unprecedented opportunities to engineer novel capabilities for the control of atom-photon interactions. In particular, photonic crystals are periodic dielectric structures that display a photonic bandgap where light cannot propagate and provide a new setting for coherent photon-mediated interactions between atoms with tunable range. Here, we report the initial observation of cooperative atom-atom interactions around the band edge of a photonic crystal waveguide. Our experiment opens the door to fascinating scenarios, such as exploring many-body physics with large spin exchange energies and low dissipation.