Repulsively bound atom pairs in an optical lattice

TL;DR

This paper reports the first experimental observation of stable, long-lived pairs of ultracold atoms bound by repulsive interactions within an optical lattice, demonstrating a novel quantum state with potential applications in quantum simulation.

Contribution

It provides the first experimental evidence of repulsively bound atom pairs in an optical lattice, confirming theoretical predictions and highlighting their unique properties.

Findings

Repulsively bound pairs exhibit long lifetimes even during collisions.

Signatures of these pairs are observed in momentum distribution and spectroscopic measurements.

Such pairs have no analogue in traditional condensed matter systems.

Abstract

Throughout physics, stable composite objects are usually formed via attractive forces, which allow the constituents to lower their energy by binding together. Repulsive forces separate particles in free space. However, in a structured environment such as a periodic potential and in the absence of dissipation, stable composite objects can exist even for repulsive interactions. Here we report on the first observation of such an exotic bound state, comprised of a pair of ultracold atoms in an optical lattice. Consistent with our theoretical analysis, these repulsively bound pairs exhibit long lifetimes, even under collisions with one another. Signatures of the pairs are also recognised in the characteristic momentum distribution and through spectroscopic measurements. There is no analogue in traditional condensed matter systems of such repulsively bound pairs, due to the presence of strong decay channels. These results exemplify on a new level the strong correspondence between the optical lattice physics of ultracold bosonic atoms and the Bose-Hubbard model, a correspondence which is vital for future applications of these systems to the study of strongly correlated condensed matter systems and to quantum information.