title: Greenberger-Horne-Zeilinger states and few-body Hamiltonians.
abstract: The generation of Greenberger-Horne-Zeilinger (GHZ) states is a crucial problem in quantum information. We derive general conditions for obtaining GHZ states as eigenstates of a Hamiltonian. We find that a necessary condition for an n-qubit GHZ state to be a nondegenerate eigenstate of a Hamiltonian is the presence of m-qubit couplings with m≥[(n+1)/2]. Moreover, we introduce a Hamiltonian with a GHZ eigenstate and derive sufficient conditions for the removal of the degeneracy.
authors.affiliation: Dipartimento di Matematica and MECENAS, Università di Bari, I-70125 Bari, Italy.
authors.forename: Paolo
authors.initials: P
authors.lastname: Facchi
authors.forename: Giuseppe
authors.initials: G
authors.lastname: Florio
authors.forename: Saverio
authors.initials: S
authors.lastname: Pascazio
authors.forename: Francesco V
authors.initials: FV
authors.lastname: Pepe