We demonstrate $|W⟩$ state encoding of multiatom ensemble qubits. Using optically trapped Rb atoms, the $T_2$ coherence time is 2.6(3) ms for $\overline{N}=7.6$ atoms and scales approximately inversely with the number of atoms. Strong Rydberg blockade between two ensemble qubits is demonstrated with a fidelity of 0.89(1), and with a fidelity of $\sim 1.0$ when postselected on a control ensemble excitation. These results are a significant step towards deterministic entanglement of atomic ensembles.

• Received 16 January 2015

DOI:https://doi.org/10.1103/PhysRevLett.115.093601