Article

Hidden two-qubit dynamics of a four-level Josephson circuit

  • Nature Communications 5, Article number: 5617 (2014)
  • doi:10.1038/ncomms6617
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Abstract

Multi-level control of quantum coherence exponentially reduces communication and computation resources required for a variety of applications of quantum information science. However, it also introduces complex dynamics to be understood and controlled. These dynamics can be simplified and made intuitive by employing group theory to visualize certain four-level dynamics in a ‘Bell frame’ comprising an effective pair of uncoupled two-level qubits. We demonstrate control of a Josephson phase qudit with a single multi-tone excitation, achieving successive population inversions between the first and third levels and highlighting constraints imposed by the two-qubit representation. Furthermore, the finite anharmonicity of our system results in a rich dynamical evolution, where the two Bell-frame qubits undergo entangling–disentangling oscillations in time, explained by a Cartan gate decomposition representation. The Bell frame constitutes a promising tool for control of multi-level quantum systems, providing an intuitive clarity to complex dynamics.

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Acknowledgements

We acknowledge the support of ISF Bikura Grant No. 1567/12 and ERC Grant No. 335933. We thank Christiane Koch for fruitful discussion.

Author information

Author notes

    • Elisha Svetitsky
    •  & Haim Suchowski

    These authors contributed equally to this work

Affiliations

  1. Racah Institute of Physics, The Hebrew University of Jerusalem, Jerusalem 91904, Israel

    • Elisha Svetitsky
    • , Roy Resh
    • , Yoni Shalibo
    •  & Nadav Katz
  2. NSF Nanoscale Science and Engineering Center, Etcheverry Hall, University of California, Berkeley, California 94720, USA

    • Haim Suchowski
  3. Raymond and Beverly Sackler School of Physics and Astronomy, Tel Aviv University, Tel Aviv 69978, Israel

    • Haim Suchowski
  4. Department of Physics, University of California, Santa Barbara, California 93106, USA

    • John M. Martinis

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Contributions

E.S., H.S., R.R. and N.K. designed the experiment. E.S., R.R. and Y.S. set up the experimental infrastructure. J.M.M. and N.K. participated in fabrication of the phase qudit. E.S. took the data. E.S., H.S. and N.K. analysed the experimental results. E.S. and R.R. performed numerical simulations. E.S., H.S. and N.K. wrote the manuscript.

Competing interests

The authors declare no competing financial interests.

Corresponding author

Correspondence to Elisha Svetitsky.

Supplementary information

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    Supplementary Information

    Supplementary Figures 1-2, Supplementary Notes 1-2.

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