Trapping and controlling atoms is one of the technical foundations for utilising their quantum mechanical properties – for example, for secure communication in quantum networks or in quantum computing. Many novel quantum devices rely on the interconnection of atoms using light: For example, atoms are trapped and held near tiny light-guiding structures to enable efficient communication between the quantum particles. Until now, multiple laser beams were required to keep the atoms in place within such nanophotonic systems.

New approach combines light and naturally occurring electrostatic forces

The research group ‘Fundamentals of Optics and Photonics’ led by Prof. Dr Arno Rauschenbeutel at the Institute of Physics, Humboldt-Universität zu Berlin (HU), has now developed a simpler and fundamentally different approach. The researchers trap laser-cooled atoms using a combination of light and naturally occurring electrostatic forces, and hold them near an ultra-thin glass fibre (100 times thinner than a single hair). Using this approach, they were able to significantly improve the stability and coherence of the trapped atoms compared to previous experiments: the atoms remained in the ‘trap’ for twice as long, and the quantum information could be stored ten times longer. The study, in which the researchers demonstrate the new experimental approach, was recently published in the renowned journal Nature Photonics.

Quantum information stored in atoms is preserved more effectively

For their approach, the quantum researchers do not rely on laser light to attract atoms to the ultra-thin glass fibre. Instead, their approach makes use of the electrostatic forces that occur naturally on the surface of the glass fibre. In their study, they demonstrate how the surface forces attract the atoms, whilst an additional laser field gently pushes them away from the surface – thereby creating a stable trapping region. Although the resulting trap holds the atoms less tightly than conventional traps, the team succeeded in transferring atoms to it efficiently, with hardly any atoms being lost. Once inside the trap, the atoms remained ‘trapped’ for a surprisingly long period of time and preserved their quantum properties far better than in previous experiments with such nanophotonic systems. This improvement is due to the fact that the atoms are kept in regions with very low light for most of the time. This reduces disturbances that can degrade delicate quantum states, allowing quantum information stored in the atoms to remain intact much longer.

“Powerful new tool for controlling quantum particles”

“This research opens up new possibilities for investigating the interactions between atoms and surfaces on extremely small scales, and introduces surface forces as a powerful new tool for controlling quantum particles. We believe that this technique could help to improve future quantum memories, quantum communication networks and other technologies based on long-lived quantum states,” explains Dr Riccardo Pennetta, lead author of the study and a postdoctoral researcher in the research group ‘Fundamentals of Optics and Photonics’ at the Department of Physics at HU. Prof. Dr Arno Rauschenbeutel, head of the research group, adds: “By showing that surface forces are not just a nuisance but that they can be useful, the study sets a new direction for the development of quantum devices. This will make optical quantum technologies both simpler and more robust in the future.”

Research Article in Nature Photonics: „Hybrid Nanophotonic Trap for Cold Atoms Using Surface Forces and a Blue-Detuned Evanescent Field “