Transverse excitations of ultracold matter waves upon propagation past   abrupt waveguide changes
  The propagation of ultracold atomic gases through abruptly changing waveguide potentials is examined in the limit of non-interacting atoms. Time-independent scattering calculations of microstructured waveguides with discontinuous changes in the transverse harmonic binding potentials are used to mimic waveguide perturbations and imperfections. Three basic configurations are examined: step-like, barrier-like and well-like with waves incident in the ground mode. At low energies, the spectra rapidly depart from single-moded, with significant transmission and reflection of excited modes. The high-energy limit sees 100 percent transmission, with the distribution of the transmitted modes determined simply by the overlap of the mode wave functions and interference. 
M. Koehler, M. W. J. Bromley, B. D. Esry (Kansas State University)