  We present a set of practical benchmarks for $N$-qubit arrays that
economically test the fidelity of achieving multi-qubit nonclassicality. The
benchmarks are measurable correlators similar to 2-qubit Bell correlators, and
are derived from a particular set of geometric structures from the $N$-qubit
Pauli group. These structures prove the Greenberger-Horne-Zeilinger (GHZ)
theorem, while the derived correlators witness genuine $N$-partite entanglement
and establish a tight lower bound on the fidelity of particular stabilizer
state preparations. The correlators need only $M \leq N+1$ distinct measurement
settings, as opposed to the $2^{2N}-1$ settings that would normally be required
to tomographically verify their associated stabilizer states. We optimize the
measurements of these correlators for a physical array of qubits that can be
nearest-neighbor-coupled using a circuit of controlled-$Z$ gates with constant
gate depth to form $N$-qubit linear cluster states. We numerically simulate the
provided circuits for a realistic scenario with $N=3,...,9$ qubits, using
ranges of $T_1$ energy relaxation times, $T_2$ dephasing times, and
controlled-$Z$ gate-fidelities consistent with Google's 9-qubit superconducting
chip. The simulations verify the tightness of the fidelity bounds and witness
nonclassicality for all nine qubits, while also showing ample room for
improvement in chip performance.
