title: Continuous-time monitoring of Landau-Zener interference in a cooper-pair box.
abstract: Landau-Zener (LZ) tunneling can occur with a certain probability when crossing energy levels of a quantum two-level system are swept across the minimum energy separation. Here we present experimental evidence of quantum interference effects in solid-state LZ tunneling. We used a Cooper-pair box qubit where the LZ tunneling occurs at the charge degeneracy. By employing a weak nondemolition monitoring, we observe interference between consecutive LZ-tunneling events; we find that the average level occupancies depend on the dynamical phase. The system's unusually strong linear response is explained by interband relaxation. Our interferometer can be used as a high-resolution Mach-Zehnder-type detector for phase and charge.
authors.affiliation: Low Temperature Laboratory, Helsinki University of Technology, FIN-02015 HUT, Finland.
authors.forename: Mika
authors.initials: M
authors.lastname: Sillanpää
authors.forename: Teijo
authors.initials: T
authors.lastname: Lehtinen
authors.forename: Antti
authors.initials: A
authors.lastname: Paila
authors.forename: Yuriy
authors.initials: Y
authors.lastname: Makhlin
authors.forename: Pertti
authors.initials: P
authors.lastname: Hakonen