Coherence and Rydberg Blockade of Atomic Ensemble Qubits

We demonstrate |W⟩ state encoding of multiatom ensemble qubits. Using optically trapped Rb atoms, the T₂ coherence time is 2. 6 (3) ms for Nover ¯=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 ∼1. 0 when postselected on a control ensemble excitation. These results are a significant step towards deterministic entanglement of atomic ensembles.