  Randomized compiling reduces the effects of errors on quantum computers by
tailoring arbitrary Markovian errors into stochastic Pauli noise. Here we prove
that randomized compiling also tailors non-Markovian errors into local
stochastic Pauli noise and investigate the technique's limitations. We show
through analysis and numerical results that randomized compiling alters errors
in three distinct helpful ways. First, it prevents the coherent accumulation of
errors (including hard to remove crosstalk effects) across gate cycles by
destroying intercycle coherent correlations. Second, it converts individual
gate cycle errors into Pauli noise. Finally, randomized compiling reduces the
variability inherent to noisy devices. We confirm these theoretical predictions
with the IBM Quantum Experience platform and describe experimental data that
illustrates a drastic performance improvement across public devices. These
results cement the importance of randomized compiling in near- and long-term
quantum information processing.
