Rydberg blockade, Forster resonances, and quantum state measurements with different atomic species

We calculate interspecies Rydberg-Rydberg interaction strengths for the heavy alkali metals Rb and Cs. The presence of strong Forster resonances makes interspecies coupling a promising approach for long-range entanglement generation. We also provide an overview of the strongest Forster resonances for Rb-Rb and Cs-Cs using different principal quantum numbers for the two atoms. We show how interspecies coupling can be used for high fidelity quantum nondemolition state measurements with low cross-talk in qubit arrays.