  Experiments on disordered alloys suggest that spin glasses can be brought
into low-energy states faster by annealing quantum fluctuations than by
conventional thermal annealing. Due to the importance of spin glasses as a
paradigmatic computational testbed, reproducing this phenomenon in a
programmable system has remained a central challenge in quantum optimization.
Here we achieve this goal by realizing quantum critical spin-glass dynamics on
thousands of qubits with a superconducting quantum annealer. We first
demonstrate quantitative agreement between quantum annealing and time-evolution
of the Schr\"odinger equation in small spin glasses. We then measure dynamics
in 3D spin glasses on thousands of qubits, where simulation of many-body
quantum dynamics is intractable. We extract critical exponents that clearly
distinguish quantum annealing from the slower stochastic dynamics of analogous
Monte Carlo algorithms, providing both theoretical and experimental support for
a scaling advantage in reducing energy as a function of annealing time.
