Yongxi Xiao

Connectivity-induced surface-loss penalty in superconducting qubit-coupler lattices

  1. Xu-Yang Gu,
  2. Gui-Han Liang,
  3. Ming-Chuan Wang,
  4. Yongxi Xiao,
  5. Cheng-Lin Deng,
  6. Zheng-He Liu,
  7. Tian-Ming Li,
  8. Kai Xu,
  9. Zhongcheng Xiang,
  10. and Heng Fan
Recent advances in design and fabrication have increased the energy-relaxation times of isolated superconducting transmon qubits to the hundreds-of-microseconds regime, with reported
values exceeding 500 μs. However, the same progress has not automatically translated to multiqubit processors, where qubits are embedded in connected qubit-coupler lattices and often exhibit much shorter lifetimes than isolated qubits. To identify possible sources of this discrepancy, here we use finite-element simulation to investigate how surface participation ratios and the resulting surface dielectric loss change when a qubit is embedded in a flip-chip qubit-coupler lattice. Controlled comparisons show that higher connectivity can indeed lead to larger surface loss: in the simulated lattice, connecting a qubit to two and four couplers increases the surface loss by factors of 1.3 and 1.8, respectively. We attribute this change to the combined effects of added edge fields from coupling claws, field redistribution over the larger connected metal network, and hybridization with coupler modes. We further examine how this connectivity-induced surface-loss penalty depends on the geometric design parameters of both the qubit electrodes and the coupling claws, and derive guidelines for designing low-loss multiqubit processors.
arxiv pdf

Engineering a Multi-Mode Purcell Filter for Superconducting-Qubit Reset and Readout with Intrinsic Purcell Protection

  1. Xu-Yang Gu,
  2. Da'er Feng,
  3. Zhen-Yu Peng,
  4. Gui-Han Liang,
  5. Yang He,
  6. Yongxi Xiao,
  7. Ming-Chuan Wang,
  8. Yu Yan,
  9. Bing-Jie Chen,
  10. Zheng-Yang Mei,
  11. Yi-Zhou Bu,
  12. Jia-Chi Zhang,
  13. Jia-Cheng Song,
  14. Cheng-Lin Deng,
  15. Xiaohui Song,
  16. Dongning Zheng,
  17. Kai Xu,
  18. Zhongcheng Xiang,
  19. and Heng Fan
Efficient qubit reset and leakage reduction are essential for scalable superconducting quantum computing, particularly in the context of quantum error correction. However, such operations
often require additional on-chip components. Here, we propose and experimentally demonstrate a mode-efficient approach to qubit reset and readout using a multi-mode Purcell filter in a superconducting quantum circuit. We exploit the inherent multi-mode structure of a coplanar waveguide resonator, using its fundamental and second-order modes for qubit reset and readout, respectively, thereby avoiding additional circuit elements. Implemented in a flip-chip architecture, our device achieves unconditional reset with residual excitation below 1% in 220 ns, and a leakage reduction unit that selectively resets the second excited state within 62 ns. Simulations predict Purcell-limited relaxation times exceeding 1 ms over an 800 MHz bandwidth. To our knowledge, this is the first experimental trial that exploits different-order modes of a microwave resonator for distinct qubit operations, representing a new direction toward scalable, mode-efficient quantum processor design.
arxiv pdf