  Various quantum applications can be reduced to estimating expectation values,
which are inevitably deviated by operational and environmental errors. Although
errors can be tackled by quantum error correction, the overheads are far from
being affordable for near-term technologies. To alleviate the detrimental
effects of errors, quantum error mitigation techniques have been proposed,
which require no additional qubit resources. Here, we benchmark the performance
of a quantum error mitigation technique based on probabilistic error
cancellation in a trapped-ion system. Our results clearly show that effective
gate fidelities exceed physical fidelities, i.e. we surpass the break-even
point of eliminating gate errors, by programming quantum circuits. The error
rates are effectively reduced from $(1.10\pm 0.12)\times10^{-3}$ to $(1.44\pm
5.28)\times10^{-5}$ and from $(0.99\pm 0.06)\times10^{-2}$ to $(0.96\pm
0.10)\times10^{-3}$ for single- and two-qubit gates, respectively. Our
demonstration opens up the possibility of implementing high-fidelity
computations on a near-term noisy quantum device.
