Figure 24.7 — Superfluid Mott transition Figure 24.7 — Superfluid Mott transition. A Bose–Einstein condensate in a shallow two-dimensional optical lattice is described by a macroscopic wavefunction with a global phase. (a) When the condensate is released from the optical lattice, an interference pattern appears because of the phase coherence between different sites. (b) When the lattice depth is increased, the system supports a Mott insulator state: each lattice site is filled with a fixed number of atoms and phase coherence is lost, thus destroying the interference pattern when the atoms are released from the lattice.Reprinted by permission from Macmillan Publishers Ltd: Bloch, Nature Phys. 1, 23–30, copyright 2005.