Detecting Genuine Multipartite Entanglement with Two Local Measurements

We present entanglement witness operators for detecting genuine multipartite entanglement. These witnesses are robust against noise and require only two local measurement settings when used in an experiment, independent of the number of qubits. This allows detection of entanglement for an increasing number of parties without a corresponding increase in effort. The witnesses presented detect states close to Greenberger-Horne-Zeilinger, cluster, and graph states. Connections to Bell inequalities are also discussed.

Figure 1

(a) Measurement settings needed for detecting genuine multiqubit entanglement close to GHZ states with Bell inequalities. For each qubit the measured spin component is indicated. (b) Settings needed for the approach presented in this paper for detecting entangled states close to GHZ states and (c) cluster states.