Amin Hosseinkhani

A Superconducting Qubit-Resonator Quantum Processor with Effective All-to-All Connectivity

  1. Michael Renger,
  2. Jeroen Verjauw,
  3. Nicola Wurz,
  4. Amin Hosseinkhani,
  5. Caspar Ockeloen-Korppi,
  6. Wei Liu,
  7. Aniket Rath,
  8. Manish J. Thapa,
  9. Florian Vigneau,
  10. Elisabeth Wybo,
  11. Ville Bergholm,
  12. Chun Fai Chan,
  13. Bálint Csatári,
  14. Saga Dahl,
  15. Rakhim Davletkaliyev,
  16. Rakshyakar Giri,
  17. Daria Gusenkova,
  18. Hermanni Heimonen,
  19. Tuukka Hiltunen,
  20. Hao Hsu,
  21. Eric Hyyppä,
  22. Joni Ikonen,
  23. Tyler Jones,
  24. Shabeeb Khalid,
  25. Seung-Goo Kim,
  26. Miikka Koistinen,
  27. Anton Komlev,
  28. Janne Kotilahti,
  29. Vladimir Kukushkin,
  30. Julia Lamprich,
  31. Alessandro Landra,
  32. Lan-Hsuan Lee,
  33. Tianyi Li,
  34. Per Liebermann,
  35. Sourav Majumder,
  36. Janne Mäntylä,
  37. Fabian Marxer,
  38. Arianne Meijer - van de Griend,
  39. Vladimir Milchakov,
  40. Jakub Mrożek,
  41. Jayshankar Nath,
  42. Tuure Orell,
  43. Miha Papič,
  44. Matti Partanen,
  45. Alexander Plyushch,
  46. Stefan Pogorzalek,
  47. Jussi Ritvas,
  48. Pedro Figuero Romero,
  49. Ville Sampo,
  50. Marko Seppälä,
  51. Ville Selinmaa,
  52. Linus Sundström,
  53. Ivan Takmakov,
  54. Brian Tarasinski,
  55. Jani Tuorila,
  56. Olli Tyrkkö,
  57. Alpo Välimaa,
  58. Jaap Wesdorp,
  59. Ping Yang,
  60. Liuqi Yu,
  61. Johannes Heinsoo,
  62. Antti Vepsäläinen,
  63. William Kindel,
  64. Hsiang-Sheng Ku,
  65. and Frank Deppe
In this work we introduce a superconducting quantum processor architecture that uses a transmission-line resonator to implement effective all-to-all connectivity between six transmon
qubits. This architecture can be used as a test-bed for algorithms that benefit from high connectivity. We show that the central resonator can be used as a computational element, which offers the flexibility to encode a qubit for quantum computation or to utilize its bosonic modes which further enables quantum simulation of bosonic systems. To operate the quantum processing unit (QPU), we develop and benchmark the qubit-resonator conditional Z gate and the qubit-resonator MOVE operation. The latter allows for transferring a quantum state between one of the peripheral qubits and the computational resonator. We benchmark the QPU performance and achieve a genuinely multi-qubit entangled Greenberger-Horne-Zeilinger (GHZ) state over all six qubits with a readout-error mitigated fidelity of 0.86.
arxiv pdf

Charge-parity switching effects and optimisation of transmon-qubit design parameters

  1. Miha Papič,
  2. Jani Tuorila,
  3. Adrian Auer,
  4. Inés de Vega,
  5. and Amin Hosseinkhani
Enhancing the performance of noisy quantum processors requires improving our understanding of error mechanisms and the ways to overcome them. A judicious selection of qubit design parameters,
guided by an accurate error model, plays a pivotal role in improving the performance of quantum processors. In this study, we identify optimal ranges for qubit design parameters, grounded in comprehensive noise modeling. To this end, we commence by analyzing a previously unexplored error mechanism that can perturb diabatic two-qubit gates due to charge-parity switches caused by quasiparticles. We show that such charge-parity switching can be the dominant quasiparticle-related error source in a controlled-Z gate between two qubits. Moreover, we also demonstrate that quasiparticle dynamics, resulting in uncontrolled charge-parity switches, induce a residual longitudinal interaction between qubits in a tunable-coupler circuit. Our analysis of optimal design parameters is based on a performance metric for quantum circuit execution that takes into account the fidelity and frequencies of the appearance of both single and two-qubit gates in the circuit. This performance metric together with a detailed noise model enables us to find an optimal range for the qubit design parameters. Substantiating our findings through exact numerical simulations, we establish that fabricating quantum chips within this optimal parameter range not only augments the performance metric but also ensures its continued improvement with the enhancement of individual qubit coherence properties. Conversely, straying from the optimal parameter range can lead to the saturation of the performance metric. Our systematic analysis offers insights and serves as a guiding framework for the development of the next generation of transmon-based quantum processors.
arxiv pdf