Zhen-Yu Mi

Scalable Low-overhead Superconducting Non-local Coupler with Exponentially Enhanced Connectivity

  1. Haonan Xiong,
  2. Jiahui Wang,
  3. Juan Song,
  4. Jize Yang,
  5. Zenghui Bao,
  6. Yan Li,
  7. Zhen-Yu Mi,
  8. Hongyi Zhang,
  9. Hai-Feng Yu,
  10. Yipu Song,
  11. and Luming Duan
Quantum error correction codes with non-local connections such as quantum low-density parity-check (qLDPC) incur lower overhead and outperform surface codes on large-scale devices.
These codes are not applicable on current superconducting devices with nearest-neighbor connections. To rectify the deficiency in connectivity of superconducting circuit system, we experimentally demonstrate a convenient on-chip coupler of centimeters long and propose an extra coupler layer to map the qubit array to a binary-tree connecting graph. This mapping layout reduces the average qubit entangling distance from O(N) to O(logN), demonstrating an exponentially enhanced connectivity with eliminated crosstalk. The entangling gate with the coupler is performed between two fluxonium qubits, reaching a fidelity of 99.37 % while the system static ZZ rate remains as low as 144 Hz without active cancellation or circuit parameter targeting. With the scalable binary tree structure and high-fidelity non-local entanglement, novel quantum algorithms can be implemented on the superconducting qubit system, positioning it as a strong competitor to other physics systems regarding circuit connectivity.
arxiv pdf

Realization of high-fidelity perfect entangler between remote superconducting quantum processors

  1. Juan Song,
  2. Shuang Yang,
  3. Pei Liu,
  4. Guang-Ming Xue,
  5. Zhen-Yu Mi,
  6. Wen-Gang Zhang,
  7. Fei Yan,
  8. Yi-Rong Jin,
  9. and Hai-Feng Yu
Building large-scale quantum computers from smaller modules offers a solution to many formidable scientific and engineering challenges. Nevertheless, engineering high-fidelity interconnects
between modules remains challenging. In recent years, quantum state transfer (QST) has provided a way to establish entanglement between two separately packaged quantum devices. However, QST is not a unitary gate, thus cannot be directly inserted into a quantum circuit, which is widely used in recent quantum computation studies. Here we report a demonstration of a direct CNOT gate realized by the cross resonance (CR) effect between two remotely packaged quantum devices connected by a microwave cable. We achieve a CNOT gate with fidelity as high as 99.15±0.02%. The quality of the CNOT gate is verified by cross-entropy benchmarking (XEB) and further confirmed by demonstrating Bell-inequality violation. This work provides a new method to realize remote two-qubit gates. Our method can be used not only to achieve distributed quantum computing but also to enrich the topology of superconducting quantum chips with jumper lines connecting distant qubits. This advancement gives superconducting qubits broader application prospects in the fields of quantum computing and quantum simulation.
arxiv pdf