Crosstalk characterization in high-coherence multi-qudit systems*

Recent advancements in building very high-Q superconducting cavities make them excellent choices for encoding quantum information in qudits due to their long lifetimes and the access to large Hilbert spaces. Typically, a nonlinear element like a transmon is used to manipulate the state of the harmonic oscillator, which in turn inherits a small nonlinearity. When scaling up to a multi-qudit system with multiple cavity modes, this nonlinearity results in spurious inter-mode coupling which lowers the gate fidelity. In this presentation, we characterize the effects of such crosstalk by analyzing several popular control protocols. With realistic experimental parameters, we perform numerical estimation of the infidelities, which can provide insight for the development of multi-mode quantum processors.