Simulations show crosstalk-robust parallel gates on superconducting arrays up to 200 qubits
Researchers from Shenzhen University and the Quantum Science Center of the Guangdong-Hong Kong-Macao Greater Bay Area report a method for designing parallel quantum gates that resists crosstalk, validated numerically on superconducting-qubit arrays scaling up to 200 qubits (the article does not say whether physical or logical). The approach splits the system into small disjoint subsystems and optimizes robust control over each, using inverse geometric optimization for single-qubit gates and quantum optimal control with the Van Loan integral technique for multi-qubit gates. In simulations, fidelity under repeated parallel single-qubit gates decayed linearly rather than exponentially, and parallel multi-qubit gates showed an order-of-magnitude error reduction; for parallel CNOT gates the decay rate fell by about a factor of 13 versus primitive pulses. The authors, Xiaodong Yang, Ran Liu and Jun Li, also tested the method numerically on coupled nitrogen-vacancy centers and a 12-qubit nuclear-spin processor, and say it does not require prior knowledge of crosstalk strengths.