Elastic transmission of atoms through superfluid $^4$He

We investigate completely elastic transmission of atoms through a slab of strongly interacting helium superfluid by diffusion Monte Carlo (DMC) method. Both quasiparticle and condensate mediated modes of transmission have been predicted$^{1,2}$ but only quasiparticle mode has been observed$^{3,4}$. We performed numerical calculations of the transmission probability using DMC with a modified fixed-node approach to find the phase shifts of scattering states for elastic transmission process of atoms incident normal to the surface of a free standing helium slab. Transmission coefficients for different energies of the incident atom were computed. Preliminary results for the group velocity of a transmitted wave packet hint at rapid transmission with times characteristic of the virtual condensate mediated process. This work was supported in part by the University of Minnesota Supercomputing Institute. \newline [1] J.~W.~Halley et al., PRL \textbf{71}, 2429 (1993) \newline [2] A.~K.~Setty et al., PRL \textbf{79}, 3930 (1997) \newline [3] K.~A.~Lidke et al., J. Low Temp. Phys. \textbf{140}, 429 (2005) \newline [4] C.~D.~H. Williams et al., PRL \textbf{91}, 085301 (2003)