A 1D optical lattice is formed by two counter-propagating laser beams of the same polarization, which interfere to give minima and maxima separated by λ/2.
Atoms are cooled and congregate at the intensity extrema — at maxima for red-detuned lattices and minima for blue-detuned lattices.
For fermionic atoms, increasing the well depth is predicted to drive antiferromagnetic order.