Quantum reflection
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Quantum reflection is physical phenomenon of reflection of matter waves from attractive potential. This term refers to the case when the reflection of classical particle is not possible. Usually the single-dimensional case is considered, when the potential has translational symmetry in two directions, and only the only one coordinate is important. This is case of a specular refelction of a slow neutral atom from a solid state surface. The van der Waals interaction attracts the particle to the surface. The potential becomes repulsive only at small distance, when the atom feels the discrete character of surface (which is supposed to me made of atoms), which leads to the diffuse scattering. Therefore, usually the grazing incidence is used to enhance the quantum reflection. The specular reflection is possible when atoms are slow; the reflection can be described using non-relativistic quantum mechanics.
The qualitative estimate of the efficiency of quantum reflection can be done using dimensional analysis. Let m be mass of the particle and k is normal component of its wavevector. Then, the energy of the normal movement of the particle 
should ne compared to the potential U of interaction. The distance w at which E = U can be considered as the thickness of depth of the potential. The condition of the efficient quantum reflection can be written as kw < 1.
The quantum reflection can be enhanced using the ridged mirrors. The mirror consisting of a set of narrow ridges allows to reduce the effective van der Waals constant and extend the working ranges of the grazing angle.
Quantum refelction makes possible the solid-state atomic mirrors and atomic-beam imaging systems (atomic nanoscope)
[edit] References
- H.Friedrich. Quantum reflection shields ultracold atoms. - Physics World, August 2004, p.20-22.
- D. Kouznetsov, H. Oberst. Scattering of waves at ridged mirrors. -- Phys. Rev. A, v.72, 013617 (2005)
