title: Control and measurement of three-qubit entangled states.
abstract: We report the deterministic creation of maximally entangled three-qubit states-specifically the Greenberger-Horne-Zeilinger (GHZ) state and the W state-with a trapped-ion quantum computer. We read out one of the qubits selectively and show how GHZ and W states are affected by this local measurement. Additionally, we demonstrate conditional operations controlled by the results from reading out one qubit. Tripartite entanglement is deterministically transformed into bipartite entanglement by local operations only. These operations are the measurement of one qubit of a GHZ state in a rotated basis and, conditioned on this measurement result, the application of single-qubit rotations.
authors.affiliation: Institut für Experimentalphysik, Universität Innsbruck, Technikerstrasse 25, A-6020 Innsbruck, Austria.
authors.forename: Christian F
authors.initials: CF
authors.lastname: Roos
authors.forename: Mark
authors.initials: M
authors.lastname: Riebe
authors.forename: Hartmut
authors.initials: H
authors.lastname: Häffner
authors.forename: Wolfgang
authors.initials: W
authors.lastname: Hänsel
authors.forename: Jan
authors.initials: J
authors.lastname: Benhelm
authors.forename: Gavin P T
authors.initials: GP
authors.lastname: Lancaster
authors.forename: Christoph
authors.initials: C
authors.lastname: Becher
authors.forename: Ferdinand
authors.initials: F
authors.lastname: Schmidt-Kaler
authors.forename: Rainer
authors.initials: R
authors.lastname: Blatt