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Creating, manipulating and detecting entangled spin pairs in optical superlattices


Over the past decade, ultracold atoms in optical lattices have proven to provide versatile grounds for the study of fundamental condensed matter phenomena. The ever increasing number of detection and manipulation methods together with the variety of accessible lattice geometries allows one to gain deep insight into ground state properties, excitations and dynamics of interacting many-body systems. On the other hand, these systems can be seen as arrays of "micro-laboratories" in which few atoms can be controlled in a highly parallel way.

In our experiments, we made use of a two-color optical superlattice with a unit cell of two lattice sites to create and manipulate pairs of atoms with opposite magnetic moments or "effective spin" to obtain large arrays of effective-spin entangled triplet or singlet pairs. A novel probe based on a spin-blockade effect was used to distinguish the two, hence constituting a measurement of nearest-neighbor spin correlations. Superexchange interactions induced between neighboring triplet or singlet pairs could be applied to further stretch the entangled pairs – or even to create large entangled many-body states in a single step. These states may serve as resource states for measurement based quantum computation in optical lattices.

Recently, the setup was extended by a second superlattice in a perpendicular direction, extending the unit cell from two to four sites. Within these square plaquettes, we observed a valence bond resonance between the two possible parallel configurations of two singlet pairs. Furthermore, we were able to dynamically create minimal versions of resonating valence bond states, both with s-wave and d-wave symmetry. Those two states may be used to encode a minimum instance of a topologically protected qubit.