Shiheng Li

Mitigating cosmic ray-like correlated events with a modular quantum processor

  1. Xuntao Wu,
  2. Yash J. Joshi,
  3. Haoxiong Yan,
  4. Gustav Andersson,
  5. Alexander Anferov,
  6. Christopher R. Conner,
  7. Bayan Karimi,
  8. Amber M. King,
  9. Shiheng Li,
  10. Howard L. Malc,
  11. Jacob M. Miller,
  12. Harsh Mishra,
  13. Hong Qiao,
  14. Minseok Ryu,
  15. Siyuan Xing,
  16. Jian Shi,
  17. and Andrew N. Cleland
Quantum processors based on superconducting qubits are being scaled to larger qubit numbers, enabling the implementation of small-scale quantum error correction codes. However, catastrophic
chip-scale correlated errors have been observed in these processors, attributed to e.g. cosmic ray impacts, which challenge conventional error-correction codes such as the surface code. These events are characterized by a temporary but pronounced suppression of the qubit energy relaxation times. Here, we explore the potential for modular quantum computing architectures to mitigate such correlated energy decay events. We measure cosmic ray-like events in a quantum processor comprising a motherboard and two flip-chip bonded daughterboard modules, each module containing two superconducting qubits. We monitor the appearance of correlated qubit decay events within a single module and across the physically separated modules. We find that while decay events within one module are strongly correlated (over 85%), events in separate modules only display ∼2% correlations. We also report coincident decay events in the motherboard and in either of the two daughterboard modules, providing further insight into the nature of these decay events. These results suggest that modular architectures, combined with bespoke error correction codes, offer a promising approach for protecting future quantum processors from chip-scale correlated errors.
arxiv pdf

Modular quantum processor with an all-to-all reconfigurable router

  1. Xuntao Wu,
  2. Haoxiong Yan,
  3. Gustav Andersson,
  4. Alexander Anferov,
  5. Ming-Han Chou,
  6. Christopher R. Conner,
  7. Joel Grebel,
  8. Yash J. Joshi,
  9. Shiheng Li,
  10. Jacob M. Miller,
  11. Rhys G. Povey,
  12. Hong Qiao,
  13. and Andrew N. Cleland
Superconducting qubits provide a promising approach to large-scale fault-tolerant quantum computing. However, qubit connectivity on a planar surface is typically restricted to only
a few neighboring qubits. Achieving longer-range and more flexible connectivity, which is particularly appealing in light of recent developments in error-correcting codes, however usually involves complex multi-layer packaging and external cabling, which is resource-intensive and can impose fidelity limitations. Here, we propose and realize a high-speed on-chip quantum processor that supports reconfigurable all-to-all coupling with a large on-off ratio. We implement the design in a four-node quantum processor, built with a modular design comprising a wiring substrate coupled to two separate qubit-bearing substrates, each including two single-qubit nodes. We use this device to demonstrate reconfigurable controlled-Z gates across all qubit pairs, with a benchmarked average fidelity of 96.00%±0.08% and best fidelity of 97.14%±0.07%, limited mainly by dephasing in the qubits. We also generate multi-qubit entanglement, distributed across the separate modules, demonstrating GHZ-3 and GHZ-4 states with fidelities of 88.15%±0.24% and 75.18%±0.11%, respectively. This approach promises efficient scaling to larger-scale quantum circuits, and offers a pathway for implementing quantum algorithms and error correction schemes that benefit from enhanced qubit connectivity.
arxiv pdf