  As we approach the era of quantum advantage, when quantum computers (QCs) can
outperform any classical computer on particular tasks, there remains the
difficult challenge of how to validate their performance. While algorithmic
success can be easily verified in some instances such as number factoring or
oracular algorithms, these approaches only provide pass/fail information for a
single QC. On the other hand, a comparison between different QCs on the same
arbitrary circuit provides a lower-bound for generic validation: a quantum
computation is only as valid as the agreement between the results produced on
different QCs. Such an approach is also at the heart of evaluating metrological
standards such as disparate atomic clocks. In this paper, we report a
cross-platform QC comparison using randomized and correlated measurements that
results in a wealth of information on the QC systems. We execute several
quantum circuits on widely different physical QC platforms and analyze the
cross-platform fidelities.
