Computing with optical lattices
Figure 3
(a) Controlled interactions between atoms on different lattice sites are possible with the help of spin-dependent lattice potentials. In such a potential, atoms in one internal state experience a potential that is different to that experienced by atoms in another internal state. These lattices can be moved relative to each other such that two initially separated atoms can be brought into controlled contact. (b) This can be extended to form a massive parallel quantum-gate array. Consider a string of atoms on different lattice sites. First the atoms are placed in a coherent superposition of the two internal states (represented by red and blue). Spin-dependent potentials are then used to "split" each atom such that it simultaneously moves to the right and to the left, and is brought into contact with the neighbouring atoms. Here, both atoms interact and a controlled phase shift, φ, is introduced between them. After such a controlled collision the atoms are again moved back to their original lattice sites.