Measuring and quantifying classical crosstalk in multi-qubit superconducting circuits

In the most general sense, crosstalk is used to describe the unwanted interactions on elements of a quantum processor due to targeted drives on non-local elements. For superconducting circuits, we use "classical crosstalk” specifically to describe crosstalk that is a result of the microwave environment of the chip, and is not a direct consequence of the qubit frequency arrangement or the drive Hamiltonians. Such crosstalk can be an important source of gate infidelity. Here, we shall present techniques to measure and quantify classical crosstalk, and use them to probe the microwave environment of our chips. These techniques could serve as a useful guide for the design and packaging of large multi-qubit devices.