title: Geometric phases for mixed states in interferometry.
abstract: We provide a physical prescription based on interferometry for introducing the total phase of a mixed state undergoing unitary evolution, which has been an elusive concept in the past. We define the parallel transport condition that provides a connection form for obtaining the geometric phase for mixed states. The expression for the geometric phase for mixed state reduces to well known formulas in the pure state case when a system undergoes noncyclic and unitary quantum evolution.
authors.affiliation: Department of Quantum Chemistry, Uppsala University, Box 518, Se-751 20 Uppsala, Sweden.
authors.forename: E
authors.initials: E
authors.lastname: Sjöqvist
authors.forename: A K
authors.initials: AK
authors.lastname: Pati
authors.forename: A
authors.initials: A
authors.lastname: Ekert
authors.forename: J S
authors.initials: JS
authors.lastname: Anandan
authors.forename: M
authors.initials: M
authors.lastname: Ericsson
authors.forename: D K
authors.initials: DK
authors.lastname: Oi
authors.forename: V
authors.initials: V
authors.lastname: Vedral