  Confining particles in hollow-core photonic crystal fibers has opened up new
prospects to scale up the distance and time over which particles can be made to
interact with light. However, maintaining long-lived quantum spin coherence
and/or transporting it over macroscopic distances in a waveguide remain
challenging. Here, we demonstrate coherent guiding of ground-state
superpositions of 85Rb atoms over a centimeter range and hundreds of
milliseconds inside a hollow-core photonic crystal fiber. The decoherence is
mainly due to dephasing from residual differential light shift (DLS) from the
optical trap and the inhomogeneity of ambient magnetic field. Our experiment
establishes an important step towards a versatile platform that can lead to
applications in quantum information networks and matter wave circuit for
quantum sensing.
