"Motion of Ultracold Atoms Bound to Optical Nanofibers: From Understanding Heating to Probing Surface Physics"
In recent years, it has become feasible to trap and control ensembles of individual atoms in the optical near-field of nanoscale photonic structures such as optical nanofibers and photonic crystal cavities. These nanophotonic atom-photon interfaces are attractive because they provide strong light-matter interaction and promise great flexibility in designing their photonic properties. Moreover, they allow to trap atoms at distances of only a few hundred nanometers from a surface. However, the heating rates of the atomic motion are orders of magnitude larger than in comparable free-space traps. This strong heating hampers the use of nanophotonic traps in more involved experiments or for quantum information processing. Still, its origin had previously remained elusive.
We have recently identified a set of thermally excited mechanical modes of the waveguide as the source of the strong heating in nanofiber-based traps . We were able to predict atom heating rates in excellent quantitative agreement with experimental observations by carefully analyzing the influence of vibrational modes on the guided light fields. This understanding enabled us to propose ways to minimize the heating and overcome a main limitation of current nanophotonic cold-atom systems.
Furthermore, advances like the success in trapping atoms at a distances of a few hundred nanometers from a surface have led to speculations whether it is possible to control atoms even closer to surfaces. At such small distances, dispersion forces dominate over optical forces and can lead to adsorption of atoms on the surface of the photonic structure. We are currently exploring the possibility of performing spectroscopy of highly excited motional states of atoms bound to a nanofiber through dispersion and optical forces. We find that the phonon-induced linewidths of such states are sufficiently small, resulting in a clearly quantized motional spectrum. The detection of these states would constitute an important step towards investigating and manipulating the dynamics of atoms on surfaces using light.