Spectator Leakage Elimination in CZ Gates via Tunable Coupler Interference on a Superconducting Quantum Processor

  1. Peng Wang,
  2. Bin-Han Lu,
  3. Tian-Le Wang,
  4. Sheng Zhang,
  5. Zhao-Yun Chen,
  6. Hai-Feng Zhang,
  7. Ren-Ze Zhao,
  8. Xiao-Yan Yang,
  9. Ze-An Zhao,
  10. Zhuo-Zhi Zhang,
  11. Xiang-Xiang Song,
  12. Yu-Chun Wu,
  13. Peng Duan,
  14. and Guo-Ping Guo
Spectator-induced leakage poses a fundamental challenge to scalable quantum computing, particularly as frequency collisions become unavoidable in multi-qubit processors. We introduce
a leakage mitigation strategy based on dynamically reshaping the system Hamiltonian. Our technique utilizes a tunable coupler to enforce a block-diagonal structure on the effective Hamiltonian governing near-resonant spectator interactions, confining the gate dynamics to a two-dimensional invariant subspace and thus preventing leakage by construction. On a multi-qubit superconducting processor, we experimentally demonstrate that this dynamic control scheme suppresses leakage rates to the order of 10−4 across a wide near-resonant detuning range. The method also scales effectively with the number of spectators. With three simultaneous spectators, the total leakage remains below the threshold relevant for surface code error correction. This approach eases the tension between dense frequency packing and high-fidelity gate operation, establishing dynamic Hamiltonian engineering as an essential tool for advancing fault-tolerant quantum computing.

Experimental Implementation of Short-Path Non-adiabatic Geometric Gates in a Superconducting Circuit

  1. Xin-Xin Yang,
  2. Liang-Liang Guo,
  3. Hai-Feng Zhang,
  4. Lei Du,
  5. Chi Zhang,
  6. Hao-Ran Tao,
  7. Yong Chen,
  8. Peng Duan,
  9. Zhi-Long Jia,
  10. Wei-Cheng Kong,
  11. and Guo-Ping Guo
The non-adiabatic geometric quantum computation (NGQC) has attracted a lot of attention for noise-resilient quantum control. However, previous implementations of NGQC require long evolution
paths that make them more vulnerable to incoherent errors than their dynamical this http URL this work, we experimentally realize a universal short-path non-adiabatic geometric gate set (SPNGQC) with a 2-times shorter evolution path on a superconducting quantum processor. Characterizing with both quantum process tomography and randomized benchmarking methods, we report an average single-qubit gate fidelity of 99.86% and a two-qubit gate fidelity of 97.9%. Additionally, we demonstrate superior robustness of single-qubit SP-NGQC gate to Rabi frequency error in some certain parameter space by comparing their performance to those of the dynamical gates and the former NGQC gates.

Anti-crosstalk high-fidelity state discrimination for superconducting qubits

  1. Zi-Feng Chen,
  2. Qi Zhou,
  3. Peng Duan,
  4. Wei-Cheng Kong,
  5. Hai-Feng Zhang,
  6. and Guo-Ping Guo
Measurement for qubits plays a key role in quantum computation. Current methods for classifying states of single qubit in a superconducting multi-qubit system produce fidelities lower
than expected due to the existence of crosstalk, especially in case of frequency crowding. Here, We make the digital signal processing (DSP) system used in measurement into a shallow neural network and train it to be an optimal classifier to reduce the impact of crosstalk. The experiment result shows the crosstalk-induced readout error deceased by 100% after a 3-second optimization applied on the 6-qubit superconducting quantum chip.