Multipartite entanglement generation and contextuality tests using non-destructive three-qubit parity measurements

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We report on the realization and application of non-destructive three-qubit parity measurements on nuclear spin qubits in diamond.

• We use high-fidelity quantum logic to map the parity of the joint state of three nuclear spin qubits onto an electronic spin qubit that acts as an ancilla, followed by single-shot non-destructive readout of the ancilla combined with an electron spin echo to ensure outcome-independent evolution of the nuclear spins.
• Through the sequential application of three such parity measurements, we demonstrate the generation of genuine multipartite entangled states out of the maximally mixed state.
• Furthermore, we implement a single-shot version of the GHZ experiment that can generate a quantum versus classical contradiction in each run.