J. Mutus

Optimal quantum control using randomized benchmarking

  1. J. Kelly,
  2. R. Barends,
  3. B. Campbell,
  4. Y. Chen,
  5. Z. Chen,
  6. B. Chiaro,
  7. A. Dunsworth,
  8. A. G. Fowler,
  9. I.-C. Hoi,
  10. E. Jeffrey,
  11. A. Megrant,
  12. J. Mutus,
  13. C. Neill,
  14. P. J. J. O'Malley,
  15. C. Quintana,
  16. P. Roushan,
  17. D. Sank,
  18. A. Vainsencher,
  19. J. Wenner,
  20. T. C. White,
  21. A. N. Cleland,
  22. and John M. Martinis
We present a method for optimizing quantum control in experimental systems, using a subset of randomized benchmarking measurements to rapidly infer error. This is demonstrated to improve
single- and two-qubit gates, minimize gate bleedthrough, where a gate mechanism can cause errors on subsequent gates, and identify control crosstalk in superconducting qubits. This method is able to correct parameters to where control errors no longer dominate, and is suitable for automated and closed-loop optimization of experimental systems
arxiv pdf

Logic gates at the surface code threshold: Superconducting qubits poised for fault-tolerant quantum computing

  1. R. Barends,
  2. J. Kelly,
  3. A. Megrant,
  4. A. Veitia,
  5. D. Sank,
  6. E. Jeffrey,
  7. T. C. White,
  8. J. Mutus,
  9. A. G. Fowler,
  10. B. Campbell,
  11. Y. Chen,
  12. Z. Chen,
  13. B. Chiaro,
  14. A. Dunsworth,
  15. C. Neill,
  16. P. O'Malley,
  17. P. Roushan,
  18. A. Vainsencher,
  19. J. Wenner,
  20. A. N. Korotkov,
  21. A. N. Cleland,
  22. and John M. Martinis
A quantum computer can solve hard problems – such as prime factoring, database searching, and quantum simulation – at the cost of needing to protect fragile quantum states
from error. Quantum error correction provides this protection, by distributing a logical state among many physical qubits via quantum entanglement. Superconductivity is an appealing platform, as it allows for constructing large quantum circuits, and is compatible with microfabrication. For superconducting qubits the surface code is a natural choice for error correction, as it uses only nearest-neighbour coupling and rapidly-cycled entangling gates. The gate fidelity requirements are modest: The per-step fidelity threshold is only about 99%. Here, we demonstrate a universal set of logic gates in a superconducting multi-qubit processor, achieving an average single-qubit gate fidelity of 99.92% and a two-qubit gate fidelity up to 99.4%. This places Josephson quantum computing at the fault-tolerant threshold for surface code error correction. Our quantum processor is a first step towards the surface code, using five qubits arranged in a linear array with nearest-neighbour coupling. As a further demonstration, we construct a five-qubit Greenberger-Horne-Zeilinger (GHZ) state using the complete circuit and full set of gates. The results demonstrate that Josephson quantum computing is a high-fidelity technology, with a clear path to scaling up to large-scale, fault-tolerant quantum circuits.
arxiv pdf

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.
arxiv pdf