Nanophotonic traps for cold atoms typically have trap volumes that are orders of magnitude smaller than, e.g., free-space optical tweezers. This makes efficient loading of these traps challenging, thereby limiting the total number of atoms coupled to the nanophotonic waveguide. Here, we demonstrate that
Λ-enhanced gray-molasses (
ΛGM) can substantially increase the number of trapped atoms in a nanofiber-based cold-atom setup. Specifically, we observe a six-fold increase in the number of loaded atoms compared to conventional red-detuned polarization gradient cooling. Despite the unusually small depth of our optical trap of only 24
μK, we load about 4000 individual Cesium atoms, achieving optical depths exceeding 140 and reaching the collisional blockade regime over a length of approximately 1 mm. After loading, we perform efficient EIT-assisted cooling that is found to increase the trap storage time to 400(9) ms. This is a 5-fold improvement over the passive storage time. Remarkably, EIT-cooling also works with two co-propagating nanofiber-guided light fields and requiries only about a few hundred picowatt of optical power. Our results provide an efficient method to boost both the number of loaded atoms and the storage time of nanophotonic atom traps.
Abstract 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.