Hybrid nanophotonic trap for cold atoms using surface forces and a blue-detuned evanescent field

Interfacing trapped neutral atoms with light propagating in nanophotonic waveguides enables efficient and long-range photon-mediated atom–atom interactions. Here we demonstrate a hybrid nanophotonic trap for cold neutral atoms, which leverages surface forces for attraction and blue-detuned evanescent light for repulsion. We attribute the attractive potential to a combination of the Casimir–Polder interaction and electrostatic attraction due to charges on the waveguide surface. Despite the shallow depth of the trap, we load atoms into it via adiabatic transfer from a conventional two-colour dipole trap with an efficiency of 96(5)%. Notably, the hybrid trap supports a long atomic storage time of 140(9) ms. Moreover, it exhibits a Ramsey coherence time T₂* T 2 * = 17.8(7) ms and spin-echo coherence time T₂^ T 2 ′ = 44.7(2.5) ms, which greatly exceed previously reported values. Our results pave the way for further explorations of atom–surface interactions at the nanoscale and illustrate the potential of harnessing surface forces to enhance storage and coherence times for atoms coupled to nanophotonic waveguides. This advance offers new opportunities for neutral-atom quantum technologies.