  For quantum computations without error correction, the dynamics of a
simulation can strongly influence the overall fidelity decay rate as well as
the relative impact of different noise processes on the fidelity. Theoretical
models of Markovian noise that include incoherent Lindblad noise, gate-based
errors, and stochastic Hamiltonian noise qualitatively agree that greater
diffusion and entanglement throughout Hilbert space typically increase the
fidelity decay rate. Simulations of the gate-efficient quantum sawtooth map
support these predictions, and experiments performed on three qubits on the
IBM-Q quantum hardware platform at fixed gate count qualitatively confirm the
predictions. A pure depolarizing noise model, often used within randomized
benchmarking (RB) theory, cannot explain the observed effect, but gate-based
Lindblad models can provide an explanation. They can also estimate the
effective Lindblad coherence times during gates, and find a consistent
$2\text{-}3\times$ shorter effective $T_2$ dephasing time than reported for
idle qubits. Additionally, the observed error per CNOT gate exceeds IBM-Q's
reported value from RB by $3.0\times$ during localized dynamics and $4.5\times$
during diffusive dynamics. This demonstrates the magnitude by which RB
understates error in a complex quantum simulation due to dynamics and
crosstalk.
