Decoherence effects on the nonlocality of symmetric states
Adel Sohbi, Isabelle Zaquine, Eleni Diamanti, Damian Markham · Physical Review A · 2015
The observation of the nonlocal properties of multipartite entangled states is of great importance for quantum information protocols. Such properties, however, are fragile and may not be observed in the presence of decoherence exhibited by practical physical systems. In this work we investigate the robustness of the nonlocality of symmetric states experiencing phase and amplitude damping, using suitable Bell inequalities based on an extended version of Hardy's paradox. We derive thresholds for observing nonlocality in terms of experimental noise parameters and demonstrate the importance of the choice of the measurement bases for optimizing the robustness. For $W$ states, in the phase damping case, we show that this choice can lead to a trade-off between obtaining a high violation of the nonlocal test and optimal robustness thresholds; we also show that in this setting the nonlocality of $W$ states is particularly robust for a large number of qubits. Furthermore, we apply our techniques to the discrimination of symmetric states belonging to different entanglement classes, thus illustrating their usefulness for a wide range of practical quantum information applications.