C. M. Quintana

Diabatic gates for frequency-tunable superconducting qubits

  1. R. Barends,
  2. C. M. Quintana,
  3. A. G. Petukhov,
  4. Yu Chen,
  5. D. Kafri,
  6. K. Kechedzhi,
  7. R. Collins,
  8. O. Naaman,
  9. S. Boixo,
  10. F. Arute,
  11. K. Arya,
  12. D. Buell,
  13. B. Burkett,
  14. Z. Chen,
  15. B. Chiaro,
  16. A. Dunsworth,
  17. B. Foxen,
  18. A. Fowler,
  19. C. Gidney,
  20. M. Giustina,
  21. R. Graff,
  22. T. Huang,
  23. E. Jeffrey,
  24. J. Kelly,
  25. P. V. Klimov,
  26. F. Kostritsa,
  27. D. Landhuis,
  28. E. Lucero,
  29. M. McEwen,
  30. A. Megrant,
  31. X. Mi,
  32. J. Mutus,
  33. M. Neeley,
  34. C. Neill,
  35. E. Ostby,
  36. P. Roushan,
  37. D. Sank,
  38. K. J. Satzinger,
  39. A. Vainsencher,
  40. T. White,
  41. J. Yao,
  42. P. Yeh,
  43. A. Zalcman,
  44. H. Neven,
  45. V. N. Smelyanskiy,
  46. and John M. Martinis
We demonstrate diabatic two-qubit gates with Pauli error rates down to 4.3(2)⋅10−3 in as fast as 18 ns using frequency-tunable superconducting qubits. This is achieved by synchronizing
the entangling parameters with minima in the leakage channel. The synchronization shows a landscape in gate parameter space that agrees with model predictions and facilitates robust tune-up. We test both iSWAP-like and CPHASE gates with cross-entropy benchmarking. The presented approach can be extended to multibody operations as well.
arxiv pdf

Observation of classical-quantum crossover of 1/f flux noise and its paramagnetic temperature dependence

  1. C. M. Quintana,
  2. Yu Chen,
  3. D. Sank,
  4. A. G. Petukhov,
  5. T. C. White,
  6. Dvir Kafri,
  7. B. Chiaro,
  8. A. Megrant,
  9. R. Barends,
  10. B. Campbell,
  11. Z. Chen,
  12. A. Dunsworth,
  13. A. G. Fowler,
  14. R. Graff,
  15. E. Jeffrey,
  16. J. Kelly,
  17. E. Lucero,
  18. J. Y. Mutus,
  19. M. Neeley,
  20. C. Neill,
  21. P. J. J. O'Malley,
  22. P. Roushan,
  23. A. Shabani,
  24. A. Vainsencher,
  25. J. Wenner,
  26. H. Neven,
  27. and John M. Martinis
By analyzing the dissipative dynamics of a tunable gap flux qubit, we extract both sides of its two-sided environmental flux noise spectral density over a range of frequencies around
2kBT/h≈1GHz, allowing for the observation of a classical-quantum crossover. Below the crossover point, the symmetric noise component follows a 1/f power law that matches the magnitude of the 1/f noise near 1Hz. The antisymmetric component displays a 1/T dependence below 100mK, providing dynamical evidence for a paramagnetic environment. Extrapolating the two-sided spectrum predicts the linewidth and reorganization energy of incoherent resonant tunneling between flux qubit wells.
arxiv pdf

Characterization and reduction of microfabrication-induced decoherence in superconducting quantum circuits

  1. C. M. Quintana,
  2. A. Megrant,
  3. Z. Chen,
  4. A. Dunsworth,
  5. B. Chiaro,
  6. R. Barends,
  7. B. Campbell,
  8. Yu Chen,
  9. I.-C. Hoi,
  10. E. Jeffrey,
  11. J. Kelly,
  12. J. Y. Mutus,
  13. P. J. J. O'Malley,
  14. C. Neill,
  15. P. Roushan,
  16. D. Sank,
  17. A. Vainsencher,
  18. J. Wenner,
  19. T. C. White,
  20. A. N. Cleland,
  21. and John M. Martinis
Many superconducting qubits are highly sensitive to dielectric loss, making the fabrication of coherent quantum circuits challenging. To elucidate this issue, we characterize the interfaces
and surfaces of superconducting coplanar waveguide resonators and study the associated microwave loss. We show that contamination induced by traditional qubit lift-off processing is particularly detrimental to quality factors without proper substrate cleaning, while roughness plays at most a small role. Aggressive surface treatment is shown to damage the crystalline substrate and degrade resonator quality. We also introduce methods to characterize and remove ultra-thin resist residue, providing a way to quantify and minimize remnant sources of loss on device surfaces.
arxiv pdf

Qubit architecture with high coherence and fast tunable coupling

  1. Yu Chen,
  2. C. Neill,
  3. P. Roushan,
  4. N. Leung,
  5. M. Fang,
  6. R. Barends,
  7. J. Kelly,
  8. B. Campbell,
  9. Z. Chen,
  10. B. Chiaro,
  11. A. Dunsworth,
  12. E. Jeffrey,
  13. A. Megrant,
  14. J. Y. Mutus,
  15. P. J. J. O'Malley,
  16. C. M. Quintana,
  17. D. Sank,
  18. A. Vainsencher,
  19. J. Wenner,
  20. T. C. White,
  21. Michael R. Geller,
  22. A. N. Cleland,
  23. and John M. Martinis
We introduce a superconducting qubit architecture that combines high-coherence qubits and tunable qubit-qubit coupling. With the ability to set the coupling to zero, we demonstrate
that this architecture is protected from the frequency crowding problems that arise from fixed coupling. More importantly, the coupling can be tuned dynamically with nanosecond resolution, making this architecture a versatile platform with applications ranging from quantum logic gates to quantum simulation. We illustrate the advantages of dynamic coupling by implementing a novel adiabatic controlled-Z gate, at a speed approaching that of single-qubit gates. Integrating coherence and scalable control, our „gmon“ architecture is a promising path towards large-scale quantum computation and simulation.
arxiv pdf