E. Lucero

Scalable in-situ qubit calibration during repetitive error detection

  1. J. Kelly,
  2. R. Barends,
  3. A. G. Fowler,
  4. A. Megrant,
  5. E. Jeffrey,
  6. T. C. White,
  7. D. Sank,
  8. J. Y. Mutus,
  9. B. Campbell,
  10. Yu Chen,
  11. Z. Chen,
  12. B. Chiaro,
  13. A. Dunsworth,
  14. E. Lucero,
  15. M. Neeley,
  16. C. Neill,
  17. P. J. J. O'Malley,
  18. C. Quintana,
  19. P. Roushan,
  20. A. Vainsencher,
  21. J. Wenner,
  22. and John M. Martinis
We present a method to optimize qubit control parameters during error detection which is compatible with large-scale qubit arrays. We demonstrate our method to optimize single or two-qubit
gates in parallel on a nine-qubit system. Additionally, we show how parameter drift can be compensated for during computation by inserting a frequency drift and using our method to remove it. We remove both drift on a single qubit and independent drifts on all qubits simultaneously. We believe this method will be useful in keeping error rates low on all physical qubits throughout the course of a computation. Our method is O(1) scalable to systems of arbitrary size, providing a path towards controlling the large numbers of qubits needed for a fault-tolerant quantum computer
arxiv pdf

Digitized adiabatic quantum computing with a superconducting circuit

  1. R. Barends,
  2. A. Shabani,
  3. L. Lamata,
  4. J. Kelly,
  5. A. Mezzacapo,
  6. U. Las Heras,
  7. R. Babbush,
  8. A. G. Fowler,
  9. B. Campbell,
  10. Yu Chen,
  11. Z. Chen,
  12. B. Chiaro,
  13. A. Dunsworth,
  14. E. Jeffrey,
  15. E. Lucero,
  16. A. Megrant,
  17. J. Y. Mutus,
  18. M. Neeley,
  19. C. Neill,
  20. P. J. J. O'Malley,
  21. C. Quintana,
  22. P. Roushan,
  23. D. Sank,
  24. A. Vainsencher,
  25. J. Wenner,
  26. T. C. White,
  27. E. Solano,
  28. H. Neven,
  29. and John M. Martinis
A major challenge in quantum computing is to solve general problems with limited physical hardware. Here, we implement digitized adiabatic quantum computing, combining the generality
of the adiabatic algorithm with the universality of the digital approach, using a superconducting circuit with nine qubits. We probe the adiabatic evolutions, and quantify the success of the algorithm for random spin problems. We find that the system can approximate the solutions to both frustrated Ising problems and problems with more complex interactions, with a performance that is comparable. The presented approach is compatible with small-scale systems as well as future error-corrected quantum computers.
arxiv pdf

Measuring and Suppressing Quantum State Leakage in a Superconducting Qubit

  1. Zijun Chen,
  2. Julian Kelly,
  3. Chis Quintana,
  4. R. Barends,
  5. B. Camppbell,
  6. Yu Chen,
  7. B. Chiaro,
  8. A. Dunsworth,
  9. A. Fowler,
  10. E. Lucero,
  11. E. Jeffrey,
  12. A. Megrant,
  13. J. Mutus,
  14. M. Neeley,
  15. C. Neill,
  16. P. J. J. O'malley,
  17. P. Roushan,
  18. D. Sank,
  19. A. Vainsencher,
  20. J. Wenner,
  21. T. C. White,
  22. A. N. Korotkov,
  23. and John M. Martinis
Leakage errors occur when a quantum system leaves the two-level qubit subspace. Reducing these errors is critically important for quantum error correction to be viable. To quantify
leakage errors, we use randomized benchmarking in conjunction with measurement of the leakage population. We characterize single qubit gates in a superconducting qubit, and by refining our use of Derivative Reduction by Adiabatic Gate (DRAG) pulse shaping along with detuning of the pulses, we obtain gate errors consistently below 10−3 and leakage rates at the 10−5 level. With the control optimized, we find that a significant portion of the remaining leakage is due to incoherent heating of the qubit.
arxiv pdf

Multiplexed dispersive readout of superconducting phase qubits

  1. Yu Chen,
  2. D. Sank,
  3. P. O'Malley,
  4. T. White,
  5. R. Barends,
  6. B. Chiaro,
  7. J. Kelly,
  8. E. Lucero,
  9. M. Mariantoni,
  10. A. Megrant,
  11. C. Neill,
  12. A. Vainsencher,
  13. J. Wenner,
  14. Yi Yin,
  15. A. N. Cleland,
  16. and John M. Martinis
We introduce a frequency-multiplexed readout scheme for superconducting phase qubits. Using a quantum circuit with four phase qubits, we couple each qubit to a separate lumped-element
superconducting readout resonator, with the readout resonators connected in parallel to a single measurement line. The readout resonators and control electronics are designed so that all four qubits can be read out simultaneously using frequency multiplexing on the one measurement line. This technology provides a highly efficient and compact means for reading out multiple qubits, a significant advantage for scaling up to larger numbers of qubits.
arxiv pdf