title: Qubit state monitoring by measurement of three complementary observables.
abstract: We consider the evolution of a qubit (spin 1/2) under the simultaneous continuous measurement of three noncommuting qubit operators σ(x), σ(y), and σ(z). For identical ideal detectors, the qubit state evolves by approaching a pure state with a random direction in the Bloch vector space and by undergoing locally isotropic diffusion in the perpendicular directions. The quantum state conditioned on the complete detector record is used to assess the fidelity of classically inspired estimates based on running time averages and discrete time bin detector outputs.
authors.affiliation: Lundbeck Foundation Theoretical Center for Quantum System Research, Department of Physics and Astronomy, University of Aarhus, DK-8000 Aarhus C, Denmark.
authors.forename: Rusko
authors.initials: R
authors.lastname: Ruskov
authors.forename: Alexander N
authors.initials: AN
authors.lastname: Korotkov
authors.forename: Klaus
authors.initials: K
authors.lastname: Mølmer