We directly introduce a Bell-type inequality for four-qubit systems. Using the inequality we investigate quantum nonlocality of a generic family of states | G abcd 〉 [ Phys. Rev. A 65 052112 (2002)] and several canonical four-qubit entangled states. It has been demonstrated that the inequality is maximally violated by the so called “four-qubit the maximally entangled state | G m 〉” and it is also violated by four-qubit W state and a special family of states | G ab 00 〉. Moreover, a useful entanglement-nonlocality relationship for the family of states | G ab 00 〉 is derived. Finally, we present a scheme of preparation of the state | G m 〉 with linear optics and cross-Kerr nonlinearities.We directly introduce a Bell-type inequality for four-qubit systems. Using the inequality we investigate quantum nonlocality of a generic family of states | G abcd 〉 [ Phys. Rev. A 65 052112 (2002)] and several canonical four-qubit entangled states. It has been demonstrated that the inequality is maximally violated by the so called “four-qubit the maximally entangled state | G m 〉” and it is also violated by four-qubit W state and a special family of states | G ab 00 〉. Moreover, a useful entanglement-nonlocality relationship for the family of states | G ab 00 〉 is derived. Finally, we present a scheme of preparation of the state | G m 〉 with linear optics and cross-Kerr nonlinearities.

arXiv:1310.6300Chinese Physics BJun 25, 20158 citations

Nonlocality in pure and mixed n-qubit X states

Josep Amengual i Batle, C. H. Raymond Ooi, Ahmed Farouk +1 more

Quantum Information ProcessingDec 21, 201519 citations

Hierarchy of the nonlocal advantage of quantum coherence and Bell nonlocality

Ming‐Liang Hu, Xiaomin Wang, Heng Fan

Quantum coherence and nonlocality capture the nature of quantumness from different aspects. For the two-qubit states with a diagonal correlation matrix, we prove strictly a hierarchy between the nonlocal advantage of quantum coherence (NAQC) and Bell nonlocality by showing geometrically that the NAQC created on one qubit by local measurement on another qubit captures quantum correlation which is stronger than Bell nonlocality. For general states, our numerical results present strong evidence that this hierarchy may still hold. So the NAQC states form a subset of the states that can exhibit Bell nonlocality. We further propose a measure of NAQC that can be used for a quantitative study of it in bipartite states.Quantum coherence and nonlocality capture the nature of quantumness from different aspects. For the two-qubit states with a diagonal correlation matrix, we prove strictly a hierarchy between the nonlocal advantage of quantum coherence (NAQC) and Bell nonlocality by showing geometrically that the NAQC created on one qubit by local measurement on another qubit captures quantum correlation which is stronger than Bell nonlocality. For general states, our numerical results present strong evidence that this hierarchy may still hold. So the NAQC states form a subset of the states that can exhibit Bell nonlocality. We further propose a measure of NAQC that can be used for a quantitative study of it in bipartite states.

arXiv:1802.03540Physical Review ASep 17, 201888 citations

Bounding the persistency of the nonlocality of W states

Péter Diviánszky, Réka Trencsényi, Erika Bene +1 more

The nonlocal properties of the $W$ states are investigated under particle loss. By removing all but two particles from an $N$ -qubit $W$ state, the resulting two-qubit state is still entangled. Hence, the $W$ state has high persistency of entanglement. We ask an analogous question regarding the persistency of nonlocality [see N. Brunner and T. V\'ertesi, Phys. Rev. A 86, 042113 (2012)]. Namely, we inquire what is the minimal number of particles that must be removed from the $W$ state so that the resulting state becomes local. We bound this value in function of $N$ qubits by considering Bell nonlocality tests with two alternative settings per site. In particular, we find that this value is between $2N/5$ and $N/2$ for large $N$ . We also develop a framework to establish bounds for more than two settings per site.The nonlocal properties of the $W$ states are investigated under particle loss. By removing all but two particles from an $N$-qubit $W$ state, the resulting two-qubit state is still entangled. Hence, the $W$ state has high persistency of entanglement. We ask an analogous question regarding the persistency of nonlocality [see N. Brunner and T. V\'ertesi, Phys. Rev. A 86, 042113 (2012)]. Namely, we inquire what is the minimal number of particles that must be removed from the $W$ state so that the resulting state becomes local. We bound this value in function of $N$ qubits by considering Bell nonlocality tests with two alternative settings per site. In particular, we find that this value is between $2N/5$ and $N/2$ for large $N$. We also develop a framework to establish bounds for more than two settings per site.

arXiv:1605.05846Physical Review AApr 18, 20169 citations

The nonlocal properties of the

W

states are investigated under particle loss. By removing all but two particles from an

N

-qubit

W

state, the resulting two-qubit state is still entangled. Hence, the

W

state has high persistency of entanglement. We ask an analogous question regarding the persistency of nonlocality [see N. Brunner and T. V\'ertesi, Phys. Rev. A 86, 042113 (2012)]. Namely, we inquire what is the minimal number of particles that must be removed from the

W

state so that the resulting state becomes local. We bound this value in function of

N

qubits by considering Bell nonlocality tests with two alternative settings per site. In particular, we find that this value is between

2N/5

and

N/2

for large

N

. We also develop a framework to establish bounds for more than two settings per site.