Fannes M., Nachtergaele B., Werner , R.F.
Abundance of translation invariant pure states
on quantum spin chains
(35K, Plain TeX)

ABSTRACT.  We construct a set of translation invariant pure states of a
quantum spin chain, which is w*-dense in the set of all translation
invariant states of the chain.
Each of the approximating states has exponential decay of
correlations, and is the unique ground state of a finite range
Hamiltonian with a spectral gap above the ground state energy.