Detecting and characterizing qubit crosstalk

Quantum information processors have grown rapidly in both size and fidelity. Currently available processors comprise 5, 8, or even 16 qubits, with 1- and 2-qubit gate infidelities below 1%. One of the looming obstacles to successfully running small algorithms or quantum error correction is crosstalk: each qubit may be influenced by the state of its neighbors, or by the operations performed on those neighbors. Crosstalk could ruin any desired computation if not eliminated or mitigated. We have been developing and testing methods to detect, quantify, and characterize crosstalk so that it can be eliminated by device engineering, or mitigated through modeling and adaptation. In this talk we provide a comprehensive taxonomy of crosstalk, and present hardware-agnostic protocols to diagnose and characterize it. Finally, we demonstrate these techniques by applying them to experimental data from superconducting qubit systems, and show that we can characterize signatures of various distinct crosstalk processes.