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.

Observation of quantum many-body effects due to zero point fluctuations in superconducting circuits

  1. Sebastien Leger,
  2. Javier Puertas Martinez,
  3. Karthik Bharadwaj,
  4. Remy Dassonneville,
  5. Jovian Delaforce,
  6. Farshad Foroughi,
  7. Vladimir Milchakov,
  8. Luca Planat,
  9. Olivier Buisson,
  10. Cecile Naud,
  11. Wiebke Hasch-Guichard,
  12. Serge Florens,
  13. Izak Snyman,
  14. and Nicolas Roch
Electromagnetic fields possess zero point fluctuations (ZPF) which lead to observable effects such as the Lamb shift and the Casimir effect. In the traditional quantum optics domain,
these corrections remain perturbative due to the smallness of the fine structure constant. To provide a direct observation of non-perturbative effects driven by ZPF in an open quantum system we wire a highly non-linear Josephson junction to a high impedance transmission line, allowing large phase fluctuations across the junction. Consequently, the resonance of the former acquires a relative frequency shift that is orders of magnitude larger than for natural atoms. Detailed modelling confirms that this renormalization is non-linear and quantum. Remarkably, the junction transfers its non-linearity to about 30 environmental modes, a striking back-action effect that transcends the standard Caldeira-Leggett paradigm. This work opens many exciting prospects for longstanding quests such as the tailoring of many-body Hamiltonians in the strongly non-linear regime, the observation of Bloch oscillations, or the development of high-impedance qubits.

Fabrication and characterization of aluminum SQUID transmission lines

  1. Luca Planat,
  2. Ekaterina Al-Tavil,
  3. Javier Puertas Martinez,
  4. Remy Dassonneville,
  5. Farshad Foroughi,
  6. Sebastien Leger,
  7. Karthik Bharadwaj,
  8. Jovian Delaforce,
  9. Vladimir Milchakov,
  10. Cecile Naud,
  11. Olivier Buisson,
  12. Wiebke Hasch-Guichard,
  13. and Nicolas Roch
We report on the fabrication and characterization of 50 Ohms, flux-tunable, low-loss, SQUID-based transmission lines. The fabrication process relies on the deposition of a thin dielectric
layer (few tens of nanometers) via Atomic Layer Deposition (ALD) on top of a SQUID array, the whole structure is then covered by a non-superconducting metallic top ground plane. We present experimental results from five different samples. We systematically characterize their microscopic parameters by measuring the propagating phase in these structures. We also investigate losses and discriminate conductor from dielectric losses. This fabrication method offers several advantages. First, the SQUID array fabrication does not rely on a Niobium tri-layer process but on a simpler double angle evaporation technique. Second, ALD provides high quality dielectric leading to low-loss devices. Further, the SQUID array fabrication is based on a standard, all-aluminum process, allowing direct integration with superconducting qubits. Moreover, our devices are in-situ flux tunable, allowing mitigation of incertitude inherent to any fabrication process. Finally, the unit cell being a single SQUID (no extra ground capacitance is needed), it is straightforward to modulate the size of the unit cell periodically, allowing band-engineering. This fabrication process can be directly applied to traveling wave parametric amplifiers.