Comparison of theory and experiment: Landau-Zener transition probability for single qubits in a Leda chip

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.

Landau-Zener Transitions in an Adiabatic Quantum Computer

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 .

12 thoughts on “Comparison of theory and experiment: Landau-Zener transition probability for single qubits in a Leda chip

  1. Is the difference between the coherent and incoherent regimes just the relative sizes of your Delta parameter and the width of your macroscopic resonant tunneling peaks?

  2. MS: yes, when Delta > W the energy gap between ground and first excited states is bigger than all the energy scales in the problem and the system can’t leave the ground state during the evolution from |0> to |1> through the anticrossing.

  3. Hi Geordie,
    if I may ask, are you still OK with your schedule of a 512-qbit QC before the end of the year?

    Also, no need to ask Scott about this topic, I already did🙂

    Matteo

  4. Pingback: Bookmarks about Theory

  5. so would Scott Aaronson now consider this a qubit? … forward to see a 512-qbit or 1024-qbit DWave quantum computer soon!! Regards,. MMM …

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