title: Off-diagonal geometric phase for mixed states.
abstract: We extend the off-diagonal geometric phase [Phys. Rev. Lett. 85, 3067 (2000)]] to mixed quantal states. The nodal structure of this phase in the qubit (two-level) case is compared with that of the diagonal mixed state geometric phase [Phys. Rev. Lett. 85, 2845 (2000)]]. Extension to higher dimensional Hilbert spaces is delineated. A physical scenario for the off-diagonal mixed state geometric phase in polarization-entangled two-photon interferometry is proposed.
authors.affiliation: Department of Quantum Chemistry, Uppsala University, Box 518, Sweden. stefan@copilot.at
authors.forename: Stefan
authors.initials: S
authors.lastname: Filipp
authors.forename: Erik
authors.initials: E
authors.lastname: Sjöqvist