Constructing Quantum Matter Atom by Atom
Understanding quantum systems that contain many particles is an outstanding challenge of physics. Even if described by simple models, their complexity grows exponentially with the number of particles. Quantum simulation, the implementation of such model systems in an experiment, could be the key to the solution of this problem. In a bottom-up approach we demonstrate control over the fundamental building block of the Hubbard model. It assumes that particles only move by tunneling from one lattice site to a neighboring one and that they only interact with other particles on the same site. The smallest system featuring these properties is composed of two interacting particles that tunnel between the sites of a double-well potential. We realize this system by trapping two ultracold 6Li atoms in the ground state of a potential formed by two tightly focused laser beams. While non-interacting atoms tunnel independently between the wells, interactions correlate their motion. We demonstrate that attractive interactions lead to a pairing of the atoms, while repulsive interactions force them to populate separate wells. By combining many such double wells we aim for the deterministic preparation of larger systems and new insights into complex quantum many-body physics.