We designed a quantum circuit to prepare a permutation-symmetric maximally entangled three-qubit state called the |S〉 state and experimentally created it on an NMR quantum processor. The presence of entanglement in the state was certified by computing two different entanglement measures, namely negativity and concurrence. We used the |S〉 state in conjunction with a set of maximally incompatible local measurements, to demonstrate the maximal violation of inequality number 26 in Sliwa’s classification scheme, which is a tight Bell inequality for the (3,2,2) scenario i.e. the three party, two measurement settings and two measurement outcomes scenario.
We introduce a protocol to classify three-qubit pure states into different entanglement classes and implement it on an NMR quantum processor. The protocol is designed in such a way that the experiments performed to classify the states can also measure the amount of entanglement present in the state. The classification requires the experimental reconstruction of the correlation matrices using 13 operators. The rank of the correlation matrices provide the criteria to classify the state in one of the five classes, namely, separable, biseparable (of three types), and genuinely entangled (of two types, GHZ and W). To quantify the entanglement, a concurrence function is defined which measures the global entanglement present in the state, using the same 13 operators. Global entanglement is zero for separable states and non-zero otherwise. We demonstrate the efficacy of the protocol by implementing it on states chosen from each of the six inequivalent (under stochastic local operations and classical communication) classes for three qubits. We also implement the protocol on states picked at random from the state space of three-qubit pure states.
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