We report an experimental measurement of Landau-Zener transitions on an individual flux qubit within a multiqubit superconducting chip. The method used isolates a single qubit, tunes its tunneling amplitude $\Delta$ into the limit where $\Delta$ is much less than both the temperature $T$ and the decoherence-induced energy level broadening, and forces it to undergo a Landau-Zener transition. We find that the behavior of the qubit agrees to a high degree of accuracy with theoretical predictions for Landau-Zener transition probabilities for a double-well quantum system coupled to a nonMarkovian $1/f$ magnetic flux noise.

• Received 11 July 2008

DOI:https://doi.org/10.1103/PhysRevB.80.012507