Qubit syndrome measurements with a high fidelity Rb-Cs Rydberg gate

We demonstrate an inter-species entangling Rydberg gate between rubidium (Rb) and cesium (Cs) atoms with fidelity $\mathcal{F}=0.975\pm 0.002$. The two-species atom array enables in-place quantum non-demolition (QND) qubit measurements which are a key capability for quantum error correction. We demonstrate this functionality with multi-atom error syndrome measurements achieving QND measurement fidelities of ${\mathcal{F}}_{\mathrm{Q}\mathrm{N}\mathrm{D}}=0.933(12)$ and 0.865(17) for two- and three-qubit plaquettes, respectively.