Continuous-Time Monitoring of Landau-Zener Interference in a Cooper-Pair Box

Mika Sillanpää; Teijo Lehtinen; Antti Paila; Yuriy Makhlin; Pertti Hakonen

doi:10.1103/PhysRevLett.96.187002

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Continuous-Time Monitoring of Landau-Zener Interference in a Cooper-Pair Box

Mika Sillanpää, Teijo Lehtinen, Antti Paila, Yuriy Makhlin, Pertti Hakonen

DOI 10.1103/PhysRevLett.96.187002 · Physical Review Letters

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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.