  We report experimental observations of large Bragg reflection from arrays of
cold atoms trapped near a one-dimensional nanoscale waveguide. By using an
optical lattice in the evanescent field surrounding a nanofiber with a period
nearly commensurate with the resonant wavelength, we observe a reflectance of
up to 75% for the guided mode. Each atom behaves as a partially-reflecting
mirror and an ordered chain of about 2000 atoms is sufficient to realize an
efficient Bragg mirror. Measurements of the reflection spectra as a function of
the lattice period and the probe polarization are reported. The latter shows
the effect of the chiral character of nanoscale waveguides on this reflection.
The ability to control photon transport in 1D waveguides coupled to spin
systems would enable novel quantum network capabilities and the study of
many-body effects emerging from long-range interactions.
