  Noisy, intermediate-scale quantum (NISQ) computing devices offer
opportunities to test the principles of quantum computing but are prone to
errors arising from various sources of noise. Fluctuations in the noise itself
lead to unstable devices that undermine the reproducibility of NISQ results.
Here we characterize the reliability of NISQ devices by quantifying the
stability of essential performance metrics. Using the Hellinger distance, we
quantify the similarity between experimental characterizations of several NISQ
devices by comparing gate fidelities, duty cycles, and register addressability
across temporal and spatial scales. Our observations collected over 22 months
reveal large fluctuations in each metric that underscore the limited scales on
which current NISQ devices may be considered reliable.
