Related to the previous post: here is a new article describing observed probabilities for transitioning out of the ground state for single qubits in a 28-qubit chip designed for AQC. They match beautifully with the predictions for LZ transitions of a quantum mechanical two-level system in the presence of environments.
We report an experimental measurement of Landau-Zener transitions on an individual flux qubit within a multi-qubit superconducting chip designed for adiabatic quantum computation. 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 1/f magnetic flux noise.
Here is the last figure in the paper.
Update: Now posted to arxiv at http://arxiv.org/abs/0807.0797 .