We propose a method to reconstruct the vibrational quantum state of atoms b
ound in arbitrary periodic potentials created by an optical lattice. The vi
brational density matrix is determined from vibrational populations that ar
e measured after translations of the optical-lattice potential. These trans
lations are realized by phase shifts of the lattice laser fields. The feasi
bility of the reconstruction method is shown for a typical situation realiz
ed in recent experiments.