Nonlocality and Entanglement

Ying‐Hui Yang, Guang-Wei Mi, Shi-Jiao Geng +2 more

Abstract Strong nonlocality with genuine entanglement was first shown by Wang et al using sets of GHZ-like states in tripartite quantum systems (2021 Phys. Rev. A 104, 012 424). However, it is an open problem whether there exists strong nonlocality with genuine entanglement in four or more partite systems. In this paper, we unify two different concepts of strong nonlocality introduced by Halder et al (2019 Phys. Rev. Lett. 122, 040 403) and by Zhang et al (2019 Phys. Rev. A 99, 062108). That is, we use a concept of k-strong nonlocality instead of these two different types of strong nonlocality. A set of orthogonal quantum states is k-strong nonlocal if it is locally irreducible in every k-partition. In fact, the strong nonlocality that is usually said is 2-strong nonlocality. The smaller the k is, the stronger the nonlocality will be. A set of states is k +-strong nonlocal if the strong nonlocality of this set is stronger than k-strong nonlocality but weaker than (k − 1)-strong nonlocality. Based on these concepts, firstly, we show 2-strong nonlocality with genuine entanglement by some sets of GHZ-like states with weight d in tripartite systems. These sets are not necessarily complete bases. Secondly, we present 2-strong nonlocality with genuine entanglement for systems with four or more parties. These results solve the open problem raised by Wang et al Finally, we construct a set of GHZ-like states with n +-strong nonlocality in n-partite quantum systems.

Jordi Tura i Brugués

Lucas Tendick, Hermann Kampermann, Dagmar Bruß

We discuss the relation between entanglement and nonlocality in the hidden nonlocality scenario. Hidden nonlocality signifies nonlocality that can be activated by applying local filters to a particular state that admits a local hidden-variable model in the Bell scenario. We present a fully biseparable three-qubit bound entangled state with a local model for the most general (nonsequential) measurements. This proves for the first time that bound entangled states can admit a local model for general measurements. We furthermore show that the local model breaks down when suitable local filters are applied. Our results demonstrate the first example of activation of nonlocality in bound entanglement. Hence, we show that genuine hidden nonlocality does not imply entanglement distillability.

J. G. Cramer

Charles H. Holbrow, James N. Lloyd, Joseph C. Amato +2 more

D. WILSON, Hyunseok Jeong, M. S. KIM

Quantum nonlocality is tested for an entangled coherent state, interacting with a dissipative environment. A pure entangled coherent state violates Bell's inequality regardless of its coherent amplitude. The higher the initial nonlocality, the more rapidly quantum nonlocality is lost. The entangled coherent state can also be investigated in the framework of 2 X 2 Hilbert space. The quantum nonlocality persists longer in 2 X 2 Hilbert space. When it decoheres it is found that the entangled coherent state fails the nonlocality test, which contrasts with the fact that the decohered entangled state is always entangled.