Nicholas Bornman

Meter-scale quantum interconnects between large quantum processors

  1. Neereja M. Sundaresan,
  2. Nicholas Cotaj,
  3. Yadav Prasad Kandel,
  4. Eric Lewandowski,
  5. Christian Robert Longton,
  6. Yves Martin,
  7. Jae-woong Nah,
  8. Kathryn Pooley,
  9. Martin Sandberg,
  10. Michael Scanlon,
  11. Chi Xiong,
  12. Emanuil Sashev Yanev,
  13. David Abraham,
  14. Abhinandan Antony,
  15. Vincent Arena,
  16. Nicholas Bornman,
  17. Khanh Dang,
  18. Oliver Dial,
  19. Christopher Guarino,
  20. Gabriel Haspil,
  21. Jared Hertzberg,
  22. Kentaro Heya,
  23. Swetha Kamlapurkar,
  24. Michael Karschner,
  25. George Keefe,
  26. Eric Liniger,
  27. Laura Luo,
  28. Thomas G. McConkey,
  29. David Olson,
  30. Jason Orcutt,
  31. Dmitry Ovchinnikov,
  32. Timothy Phung,
  33. Sankeerth Rajalingam,
  34. Michael Selvanayagam,
  35. William Shanks,
  36. Dongbing Shao,
  37. Abigail Shearrow,
  38. Adam Stabile,
  39. Jiri Stehlik,
  40. Joseph Suttle,
  41. Jeng-Bang Yau,
  42. and Eric Zhang
Modular quantum architecture requires long-distance quantum interconnects to stitch together individual processor modules. Such interconnects, long-distance couplers or L-couplers,
must support coherent quantum operation over meter-scale distances and scale to multiple connections between any two modules. Here we demonstrate four L-couplers operating between two 120-qubit IBM Nighthawk R1 superconducting qubit processors. Each L-coupler joins two Nighthawk lattice qubits through two frequency-tunable L-qubits, two RF-SQUID based „i2m“ couplers, and 80 cm of superconducting aluminum coax. Each cable installs perpendicular to the processor surface, to enable denser connections, and is joined to the chip by an indium-to-indium room temperature pressure bond made after both modules were mounted. L-coupler modes near 5 GHz, with internal quality factors of 0.86 to 1.09e6, carry relay-based state transfer at a mean network benchmarking fidelity of 99.00%, with a best link of 99.29 +/- 0.07%. We then realize distant CZ gates between lattice qubits in separate modules at a mean fidelity of 94.75%, with a best link of 96.42 +/- 0.28%, and use them to generate entangled states across the two processors, including a demonstration of simultaneous Bell pair generation using two adjacent L-couplers. These four high-fidelity L-couplers establish a practical path to scalable quantum interconnects for modular quantum computing.
arxiv pdf

Ultracoherent superconducting cavity-based multiqudit platform with error-resilient control

  1. Taeyoon Kim,
  2. Tanay Roy,
  3. Xinyuan You,
  4. Andy C. Y. Li,
  5. Henry Lamm,
  6. Oleg Pronitchev,
  7. Mustafa Bal,
  8. Sabrina Garattoni,
  9. Francesco Crisa,
  10. Daniel Bafia,
  11. Doga Kurkcuoglu,
  12. Roman Pilipenko,
  13. Paul Heidler,
  14. Nicholas Bornman,
  15. David van Zanten,
  16. Silvia Zorzetti,
  17. Roni Harnik,
  18. Akshay Murthy,
  19. Shaojiang Zhu,
  20. Changqing Wang,
  21. Andre Vallieres,
  22. Ziwen Huang,
  23. Jens Koch,
  24. Anna Grassellino,
  25. Srivatsan Chakram,
  26. Alexander Romanenko,
  27. and Yao Lu
Superconducting radio-frequency (SRF) cavities offer a promising platform for quantum computing due to their long coherence times and large accessible Hilbert spaces, yet integrating
nonlinear elements like transmons for control often introduces additional loss. We report a multimode quantum system based on a 2-cell elliptical shaped SRF cavity, comprising two cavity modes weakly coupled to an ancillary transmon circuit, designed to preserve coherence while enabling efficient control of the cavity modes. We mitigate the detrimental effects of the transmon decoherence through careful design optimization that reduces transmon-cavity couplings and participation in the dielectric substrate and lossy interfaces, to achieve single-photon lifetimes of 20.6 ms and 15.6 ms for the two modes, and a pure dephasing time exceeding 40 ms. This marks an order-of-magnitude improvement over prior 3D multimode memories. Leveraging sideband interactions and novel error-resilient protocols, including measurement-based correction and post-selection, we achieve high-fidelity control over quantum states. This enables the preparation of Fock states up to N=20 with fidelities exceeding 95%, the highest reported to date to the authors‘ knowledge, as well as two-mode entanglement with coherence-limited fidelities reaching up to 99.9% after post-selection. These results establish our platform as a robust foundation for quantum information processing, allowing for future extensions to high-dimensional qudit encodings.
arxiv pdf