Realizing a quantum register using collective excitations in an atomic ensemble without a Rydberg blockade

A qubit made up of an ensemble of atoms is attractive due to its resistance to atom losses and is usually achieved using the Rydberg blockade effect. In this work, we consider a protocol to load a spin-dependent optical lattice with one atom per site from a spatially overlapping atomic ensemble without using any transitions out of the ⁸⁷Rb F=1 ground state manifold. This is achieved using a radiofrequency pulse to drive a transition between Zeeman sublevels, and a blockade effect that arises from the strong s-wave interaction between atoms in the same lattice site. Identifying each lattice site as a qubit, we demonstrate how qubit operations that are insensitive to the size of the ensemble may be performed, and how two qubits may be entangled using the ensemble.