title: Ascertaining the values of sigma x, sigma y, and sigma z of a polarization qubit.
abstract: In the 1987 spin-retrodiction puzzle of Vaidman, Aharonov, and Albert one is challenged to ascertain the values of sigma(x), sigma(y), and sigma(z) of a spin-1/2 particle by utilizing entanglement. We report the experimental realization of a quantum-optical version in which the outcome of an intermediate polarization projection is inferred by exploiting single-photon two-qubit quantum gates. The experimental success probability is consistently above the 90.2% threshold of the optimal one-qubit strategy, with an average success probability of 95.6%.
authors.affiliation: Sektion Physik, Universität München, Schellingstrasse 4, 80799 München, Germany.
authors.forename: Oliver
authors.initials: O
authors.lastname: Schulz
authors.forename: Ruprecht
authors.initials: R
authors.lastname: Steinhübl
authors.forename: Markus
authors.initials: M
authors.lastname: Weber
authors.forename: Berthold-Georg
authors.initials: BG
authors.lastname: Englert
authors.forename: Christian
authors.initials: C
authors.lastname: Kurtsiefer
authors.forename: Harald
authors.initials: H
authors.lastname: Weinfurter