  Large quantum computers promise to solve some critical problems not solvable
otherwise. However, modern quantum technologies suffer various imperfections
such as control errors and qubit decoherence, inhibiting their potential
utility. The overheads of quantum error correction are too great for near-term
quantum computers, whereas error-mitigation strategies that address specific
device imperfections may lose relevance as devices improve. To enhance the
performance of quantum computers with high-quality qubits, we introduce a
strategy based on symmetrization and nonlinear aggregation. On a commercial
trapped-ion quantum computer, it improves performance of multiple practical
algorithms by 100x with no qubit or gate overhead.
