Microwave Crosstalk Limits Qubit Scaling, Research Establishes

Researchers at ETH Zurich have identified specific circuit layouts that contribute significantly to microwave crosstalk, a major obstacle to building larger superconducting quantum devices. The work pinpoints drive lines positioned near qubits and those crossing qubit-qubit couplers using air bridges as key sources of signal interference. By designing and characterizing devices with these structures, the team developed physical models that quantitatively explain observed crosstalk, providing practical guidance for future low-crosstalk device layouts and establishing a basis for investigating subtler interference mechanisms.

Planar Device Layouts Limit Qubit Scaling via Crosstalk

Drive lines positioned close to qubits represent a significant source of microwave crosstalk, limiting the scalability of superconducting quantum devices, according to new work at ETH Zurich. The research identifies specific geometric arrangements that amplify unwanted signal leakage, hindering efforts to build larger and more complex quantum processors. This crosstalk arises from stray capacitance between the control lines and the qubits themselves, creating excess control errors that degrade performance.

The team’s analysis further pinpoints air bridge qubit-qubit couplers as particularly vulnerable to crosstalk when intersected by a drive line. Researchers developed quantitative physical models that accurately predict crosstalk levels based solely on device geometry and packaging design, filling a gap where previous studies lacked predictive capability. These models were validated against experimental data from fabricated test structures, and also successfully explained the strongest crosstalk instances observed in a 17-qubit quantum processor.