  Quantum information processing offers dramatic speedups, yet is famously
susceptible to decoherence, the process whereby quantum superpositions decay
into mutually exclusive classical alternatives, thus robbing quantum computers
of their power. This has made the development of quantum error correction an
essential and inescapable aspect of both theoretical and experimental quantum
computing. So far little is known about protection against decoherence in the
context of quantum annealing, a computational paradigm which aims to exploit
ground state quantum dynamics to solve optimization problems more rapidly than
is possible classically. Here we develop error correction for quantum annealing
and provide an experimental demonstration using up to 344 superconducting flux
qubits in processors which have recently been shown to physically implement
programmable quantum annealing. We demonstrate a substantial improvement over
the performance of the processors in the absence of error correction. These
results pave a path toward large scale noise-protected adiabatic quantum
optimization devices.
