Spectators Errors in Multiqubit Tunable Coupling Architectures

The addition of tunable couplers to superconducting quantum architectures offers significant advantages for scalability compared to fixed coupling approaches. Couplers such as the one proposed in Ref. [1] allow exact cancellation of qubit-qubit coupling by interfering the coupling through a capacitor with the coupling through a tunable qubit. However, the cancellation is necessarily narrowband, and in a multiqubit environment with stray couplings the cancellation condition can change depending on which gate is operating and even the states of the qubits. Here we investigate a modified version Ref. [1] coupler in multiqubit environment. With near-detuned qubits, we find that stray coupling can induce gate errors of order 1% when performing simultaneous gates if the microwave crosstalk is not carefully engineered.
[1] F. Yan et al. Phys. Rev. Applied. 10, 054063 (2018)