Superconducting qubit coherence metrics for device engineering

Superconducting qubit coherence has a precision problem. Relaxation time T
1
and decoherence time T
2
are by far the most common benchmarks of single qubit performance in superconducting quantum circuits, and are heavily relied upon for engineering next-generation devices. However, these metrics have strong environmental sensitivities and are temporally unstable, and thus alone are not robust metrics for describing individual qubits and comparing them against one another.In this tutorial, the measurement and interpretation of superconducting qubit coherence metrics is detailed, and useful qubit metrics are outlined that consider current knowledge of T
1
and T
2
variation sources.