  Gate set tomography (GST) provides precise, self-consistent estimates of the
noise channels for all of a quantum processor's logic gates. But GST
experiments are large, involving many distinct quantum circuits. This has
prevented their use on systems larger than two qubits. Here, we show how to
streamline GST experiment designs by removing almost all redundancy, creating
smaller and more scalable experiments without losing precision. We do this by
analyzing the "germ" subroutines at the heart of GST circuits, identifying
exactly what gate set parameters they are sensitive to, and leveraging this
information to remove circuits that duplicate other circuits' sensitivities. We
apply this technique to two-qubit GST experiments, generating streamlined
experiment designs that contain only slightly more circuits than the
theoretical minimum bounds, but still achieve Heisenberg-like scaling in
precision (as demonstrated via simulation and a theoretical analysis using
Fisher information). In practical use, the new experiment designs can match the
precision of previous GST experiments with significantly fewer circuits. We
discuss the prospects and feasibility of extending GST to three-qubit systems
using our techniques.
