  Quantum computation, a completely different paradigm of computing, benefits
from theoretically proven speed-ups for certain problems and opens up the
possibility of exactly studying the properties of quantum systems. Yet, because
of the inherent fragile nature of the physical computing elements, qubits,
achieving quantum advantages over classical computation requires extremely low
error rates for qubit operations as well as a significant overhead of physical
qubits, in order to realize fault-tolerance via quantum error correction.
However, recent theoretical work has shown that the accuracy of computation
based off expectation values of quantum observables can be enhanced through an
extrapolation of results from a collection of varying noisy experiments. Here,
we demonstrate this error mitigation protocol on a superconducting quantum
processor, enhancing its computational capability, with no additional hardware
modifications. We apply the protocol to mitigate errors on canonical single-
and two-qubit experiments and then extend its application to the variational
optimization of Hamiltonians for quantum chemistry and magnetism. We
effectively demonstrate that the suppression of incoherent errors helps unearth
otherwise inaccessible accuracies to the variational solutions using our noisy
processor. These results demonstrate that error mitigation techniques will be
critical to significantly enhance the capabilities of near-term quantum
computing hardware.
