A new study shows how a region of space could be rendered invisible to matter waves. In recent years the possibility of optical cloaking has become a hot topic (e.g., Science, 8 Sept 2006). Even cloaking with sound waves has been proposed (http://www.aip.org/pnu/2008/split/853-2.html). Now physicists in Professor Xiang Zhang’s group at the University of California, Berkeley, are trying to extend the cloaking idea to atom waves (chilled atoms whose quantum wavelike properties are more important than their particle-like properties) moving through a medium.
The “medium” in question here is a concentric optical lattice, generated by standing electromagnetic waves with spatially controlled amplitudes and phases. Cloaking of an object bathed in light works by modulating the effective mass and potential of atom waves traversing the shell surrounding the object. The shell is analogous to the metamaterials (tailored materials often consisting of arrays of tiny rods and ring-shaped metal structures) used in the optical case.
One of the Berkeley researchers, Shuang Zhang (firstname.lastname@example.org), says that the atom-wave equivalent of an index of refraction would be the modulation of the effective atomic mass inside the optical lattice (see figure at www.aip.org/png). Zhang says that apart from cloaking, the creation of a metamaterial for atom waves might also help in focusing atom waves into tiny spot (super-lensing) or for steering particle beams at will. (Zhang et al., Physical Review Letters, 28 march 2008)