Rydberg-blockade controlled-NOT gate and entanglement in a two-dimensional array of neutral-atom qubits

We present experimental results on two-qubit Rydberg-blockade quantum gates and entanglement in a twodimensional qubit array. Without postselection against atom loss we achieve a Bell state fidelity of 0.73 ± 0.05. The experiments are performed in an array of single Cs atom qubits with a site to site spacing of 3.8 μm. Using the standard protocol for a Rydberg-blockade CZ gate together with single qubit operations we create Bell states and measure their fidelity using parity oscillations. We analyze the role of ac Stark shifts that occur when using two-photon Rydberg excitation and show how to tune experimental conditions for optimal gate fidelity.