Coherent Josephson qubit suitable for scalable quantum integrated circuits

  1. R. Barends,
  2. J. Kelly,
  3. A. Megrant,
  4. D. Sank,
  5. E. Jeffrey,
  6. Y. Chen,
  7. Y. Yin,
  8. B. Chiaro,
  9. J. Mutus,
  10. C. Neill,
  11. P. O'Malley,
  12. P. Roushan,
  13. J. Wenner,
  14. T. C. White,
  15. A. N. Cleland,
  16. and John M. Martinis
We demonstrate a planar, tunable superconducting qubit with energy relaxation times up to 44 microseconds. This is achieved by using a geometry designed to both minimize radiative loss and reduce coupling to materials-related defects. At these levels of coherence, we find a fine structure in the qubit energy lifetime as a function of frequency, indicating the presence of a sparse population of incoherent, weakly coupled two-level defects. This is supported by a model analysis as well as experimental variations in the geometry. Our `Xmon‘ qubit combines facile fabrication, straightforward connectivity, fast control, and long coherence, opening a viable route to constructing a chip-based quantum computer.
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