  In this work, we demonstrate that the zero-fidelity, an approximation to the
process fidelity, when combined with randomized benchmarking, becomes robust to
state preparation and measurement (SPAM) errors. However, as randomized
benchmarking requires randomly choosing an increasingly large number of
Clifford elements from the Clifford group when the qubit number increases, this
combination is also limited to quantum systems with up to three qubits. To make
the zero-fidelity independent of SPAM errors and, at the same time, applicable
to multi-qubit systems, we employ a channel noise scaling method similar to the
method of global unitary folding, or identity scaling, used for quantum error
mitigation.
