Quantum States of Matter of Simple Bosonic Systems: BEC's, Superfluids and Quantum Solids

Abstract

The phase diagram of a single component Bose system in a lattice at zero temperature is obtained. We calculate the variational energies for the Mott insulating and superfluid phases. Below a certain critical density, which depends monotonically on the well depth of the lattice, the Mott insulating phase is stable over the superfluid phase for low enough tunelling amplitude regardless of whether the number of bosons is or is not incommensurate with the lattice. The transition is discontinuous as the superfluid order parameter jumps from a finite value to zero at the Mott transition.