  Noisy intermediate-scale quantum (NISQ) devices are valuable platforms for
testing the tenets of quantum computing, but these devices are susceptible to
errors arising from de-coherence, leakage, cross-talk and other sources of
noise. This raises concerns regarding the stability of results when using NISQ
devices since strategies for mitigating errors generally require
well-characterized and stationary error models. Here, we quantify the
reliability of NISQ devices by assessing the necessary conditions for
generating stable results within a given tolerance. We use similarity metrics
derived from device characterization data to derive and validate bounds on the
stability of a 5-qubit implementation of the Bernstein-Vazirani algorithm.
Simulation experiments conducted with noise data from IBM Washington, spanning
January 2022 to April 2023, revealed that the reliability metric fluctuated
between 41% and 92%. This variation significantly surpasses the maximum
allowable threshold of 2.2% needed for stable outcomes. Consequently, the
device proved unreliable for consistently reproducing the statistical mean in
the context of the Bernstein-Vazirani circuit.
