Thomas G. McConkey

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

Circuit quantum electrodynamics (cQED) with modular quasi-lumped models

  1. Zlatko K. Minev,
  2. Thomas G. McConkey,
  3. Maika Takita,
  4. Antonio D. Corcoles,
  5. and Jay M. Gambetta
Extracting the Hamiltonian of interacting quantum-information processing systems is a keystone problem in the realization of complex phenomena and large-scale quantum computers. The
remarkable growth of the field increasingly requires precise, widely-applicable, and modular methods that can model the quantum electrodynamics of the physical circuits, and even of their more-subtle renormalization effects. Here, we present a computationally-efficient method satisfying these criteria. The method partitions a quantum device into compact lumped or quasi-distributed cells. Each is first simulated individually. The composite system is then reduced and mapped to a set of simple subsystem building blocks and their pairwise interactions. The method operates within the quasi-lumped approximation and, with no further approximation, systematically accounts for constraints, couplings, parameter renormalizations, and non-perturbative loading effects. We experimentally validate the method on large-scale, state-of-the-art superconducting quantum processors. We find that the full method improves the experimental agreement by a factor of two over taking standard coupling approximations when tested on the most sensitive and dressed Hamiltonian parameters of the measured devices.
arxiv pdf