  Quantum processors require a signal-delivery architecture with high
addressability (low crosstalk) to ensure high performance already at the scale
of dozens of qubits. Signal crosstalk causes inadvertent driving of quantum
gates, which will adversely affect quantum-gate fidelities in scaled-up
devices. Here, we demonstrate packaged flip-chip superconducting quantum
processors with signal-crosstalk performance competitive with those reported in
other platforms. For capacitively coupled qubit-drive lines, we find
on-resonant crosstalk better than -27 dB (average -37 dB). For inductively
coupled magnetic-flux-drive lines, we find less than 0.13 % direct-current flux
crosstalk (average 0.05 %). These observed crosstalk levels are adequately
small and indicate a decreasing trend with increasing distance, which is
promising for further scaling up to larger numbers of qubits. We discuss the
implication of our results for the design of a low-crosstalk, on-chip signal
delivery architecture, including the influence of a shielding tunnel structure,
potential sources of crosstalk, and estimation of crosstalk-induced qubit-gate
error in scaled-up quantum processors.
