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arXiv:2509.17767 · Nature Photonics

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

Riccardo Pennetta, Antoine Glicenstein, Lucas Pache, Philipp Schneeweiß, Jürgen Volz, Arno Rauschenbeutel

Published Jul 9, 2026• 3 citations
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Abstract

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 $${T}_{2}^{* }$$ T 2 * = 17.8(7) ms and spin-echo coherence time $${T}_{2}^{{\prime} }$$ 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.

DOI
10.1038/s41566-026-01961-9

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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}^{* }T2∗​ T 2 * = 17.8(7) ms and spin-echo coherence time T2′{T}_{2}^{{\prime} }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.
An integrated optical dipole trap uses two-color (red and blue-detuned) traveling evanescent wave fields for trapping cold neutral atoms. To achieve longitudinal confinement, we propose using an integrated optical waveguide coupler, which provides a potential gradient along the beam propagation direction sufficient to confine atoms. This integrated optical dipole trap can support an atomic ensemble with a large optical depth due to its small mode area. Its quasi- TE 0 waveguide mode has an advantage over the HE 11 mode of a nanofiber, with little inhomogeneous Zeeman broadening at the trapping region. The longitudinal confinement eliminates the need for a one dimensional optical lattice, reducing collisional blockaded atomic loading, potentially producing larger ensembles. The waveguide trap allows for scalability and integrability with nano-fabrication technology. We analyze the potential performance of such integrated atom traps.
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We propose an optical dipole trap for cold, neutral atoms based on the electric field produced from the evanescent fields in a hollow, rectangular slot cut through an optical nanofibre. In particular, we discuss the trap performance in relation to laser-cooled rubidium atoms and show that a far off-resonance, blue-detuned field combined with the attractive surface-atom interaction potential from the dielectric material forms a stable trapping configuration. With the addition of a red-detuned field, we demonstrate how three dimensional confinement of the atoms at a distance of 140–200 nm from the fibre surface within the slot can be accomplished. This scheme facilitates optical coupling between the atoms and the nanofibre that could be exploited for quantum communication schemes using ensembles of laser-cooled atoms.
Quantum vacuum forces dictate the interaction between individual atoms and dielectric surfaces at nanoscale distances. For example, their large strengths typically overwhelm externally applied forces, which makes it challenging to controllably interface cold atoms with nearby nanophotonic systems. Here we theoretically show that it is possible to tailor the vacuum forces themselves to provide strong trapping potentials. Our proposed trapping scheme takes advantage of the attractive ground-state potential and adiabatic dressing with an excited state whose potential is engineered to be resonantly enhanced and repulsive. This procedure yields a strong metastable trap, with the fraction of excited-state population scaling inversely with the quality factor of the resonance of the dielectric structure. We analyse realistic limitations to the trap lifetime and discuss possible applications that might emerge from the large trap depths and nanoscale confinement. Atoms experience large and typically undesirable forces near dielectric surfaces due to quantum fluctuations of the electromagnetic vacuum. The work of Chang et al.proposes a scheme in which these forces can be exploited to create strong atomic traps at nanoscale distances from surfaces.
ΛΛΛ-enhanced gray-molasses loading and EIT cooling of neutral atoms in nanophotonic traps
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 ΛΛΛ-enhanced gray-molasses (ΛΛΛGM) 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 μμμK, 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.
We propose an optical dipole trap for cold neutral atoms based on the electric field produced from the evanescent fields in a hollow rectangular slot cut through an optical nanofibre. In particular, we discuss the trap performance in relation to laser-cooled rubidium atoms and show that a far off-resonance, blue-detuned field combined with the attractive surface-atom interaction potential from the dielectric material forms a stable trapping configuration. With the addition of a red-detuned field, we demonstrate how three dimensional confinement of the atoms at a distance of 140 - 200 nm from the fibre surface within the slot can be accomplished. This scheme facilitates optical coupling between the atoms and the nanofibre that could be exploited for quantum communication schemes using ensembles of laser-cooled atoms.