Cooling and entangling ultracold atoms in optical lattices.

Scalable, coherent many-body systems can enable the realization of previously unexplored quantum phases and have a potential to exponentially speed up information processing. Here we report the cooling of a quantum simulator with ten thousand atoms and mass production of high-fidelity entangled pairs. In a two-dimensional plane, we cool Mott-insulator samples by immersing them into removable superfluid reservoirs, achieving an entropy per particle of [Formula: see text] The atoms are then rearranged into a two-dimensional lattice free of defects. We further demonstrate a two-qubit gate with a fidelity of 0.993(1) for entangling 1250 atom pairs. Our results offer a setting for exploring low-energy many-body phases and could enable the creation of large-scale entanglement.