Joseph Suttle

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

Digital coherent control of a superconducting qubit

  1. Edward Leonard Jr.,
  2. Matthew A. Beck,
  3. JJ Nelson,
  4. Brad G. Christensen,
  5. Ted Thorbeck,
  6. Caleb Howington,
  7. Alexander Opremcak,
  8. Ivan V. Pechenezhskiy,
  9. Kenneth Dodge,
  10. Nicholas P. Dupuis,
  11. Jaseung Ku,
  12. Francisco Schlenker,
  13. Joseph Suttle,
  14. Christopher Wilen,
  15. Shaojiang Zhu,
  16. Maxim G. Vavilov,
  17. Britton L. T. Plourde,
  18. and Robert McDermott
High-fidelity gate operations are essential to the realization of a fault-tolerant quantum computer. In addition, the physical resources required to implement gates must scale efficiently
with system size. A longstanding goal of the superconducting qubit community is the tight integration of a superconducting quantum circuit with a proximal classical cryogenic control system. Here we implement coherent control of a superconducting transmon qubit using a Single Flux Quantum (SFQ) pulse driver cofabricated on the qubit chip. The pulse driver delivers trains of quantized flux pulses to the qubit through a weak capacitive coupling; coherent rotations of the qubit state are realized when the pulse-to-pulse timing is matched to a multiple of the qubit oscillation period. We measure the fidelity of SFQ-based gates to be ~95% using interleaved randomized benchmarking. Gate fidelities are limited by quasiparticle generation in the dissipative SFQ driver. We characterize the dissipative and dispersive contributions of the quasiparticle admittance and discuss mitigation strategies to suppress quasiparticle poisoning. These results open the door to integration of large-scale superconducting qubit arrays with SFQ control elements for low-latency feedback and stabilization.
arxiv pdf