Intrinsic Heating and Cooling in Adiabatic Processes for Bosons in Optical Lattices

We show that by raising the lattice "adiabatically" as in all current optical lattice experiments on bosons, even though the temperature may decrease initially, it will eventually rise linearly with lattice height, taking the system further away from quantum degeneracy. This increase is {\rm intrinsic} and is caused by the {\em adiabatic compression} during the raising of red detuned lattices. However, the origin of this heating, which is {\em entirely different} from that in the bulk, also shows that one can {\em reverse} the temperature rise to reach quantum degeneracy by {\em adiabatic expansion}, which can be achieved by using blue detuned lasers.