Lutsyshyn, Yaroslav2009-01-302009-01-302008-12https://hdl.handle.net/11299/47116University of Minnesota Ph.D. dissertation. December 2008. Major: Physics. Advisor: J. Woods Halley. 1 computer file (PDF); xiii-165 pages, appendices A-D.Atomic transmission experiments on superfluid helium-four may provide information about its structure. It was proposed in the past that a transmission channel is possible in which the impinging atoms couple directly to the condensate fraction in helium-II. Such a mechanism would provide an important direct probe of the off-diagonal long-range order in helium-II. We have successfully developed a method based on the diffusion Monte Carlo technique to simulate elastic transmission of atoms through a slab of helium-four at zero temperature. The scattering process is presented as a sum of appropriate standing wave scattering states. The phase factors for each scattering state are determined by matching the diffusion Monte Carlo results with correct energy of the scattering state. The scattering states effectively set the boundary conditions for the problem and in this way determine a phase factor and momentum of the incoming particle. Diffusion Monte Carlo is then performed in its fixed-node flavor. Our results suggest a possibility of complete transparency of small unbound helium films for a broad range of incoming particle's energy. Wavepacket analysis of the computed transmission coefficient's phase dependence on the incoming particle's wavevector was used to obtain times of the transmission process. Time delay analysis suggests the presence of anomalously fast transmission. Such results are strongly supportive of the original condensate mediated transmission hypothesis.en-USDiffusion Monte CarloHeliumQuantum Monte CarloScatteringSimulationSuperfluidityPhysicsThesis or Dissertation