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Advanced Quantum Technologies

New Genuinely Multipartite Entanglement

Ming‐Xing Luo

Published Dec 11, 2020• 45 citations
Publisher

Abstract

Abstract The quantum entanglement as one of the important resources has been verified by using different local models. There is no efficient method to verify single multipartite entanglement that is not generated by multisource quantum networks with local operations and shared randomness. The goal in this work is to solve this problem. First, a new local model is proposed for describing all the states that can be generated by using distributed entangled states and shared randomness without classical communication. This model is stronger than the biseparable model and implies new genuinely multipartite entanglement. With the present local model it is proved that all the permutationally symmetric entangled pure states are new genuinely multipartite entanglement. It is further proved that the new feature holds for all the multipartite entangled pure states in the biseparable model with the dimensions of local systems being not larger than three. The new multipartite entanglement is also robust against general noises. Finally, a simple Bell inequality is provided to verify new genuinely multipartite entangled pure qubit states in the present model. The results show new insight into featuring the genuinely multipartite entanglement in the distributive scenarios.

DOI
10.1002/qute.202000123

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Abstract The quantum entanglement as one of the important resources has been verified by using different local models. There is no efficient method to verify single multipartite entanglement that is not generated by multisource quantum networks with local operations and shared randomness. The goal in this work is to solve this problem. First, a new local model is proposed for describing all the states that can be generated by using distributed entangled states and shared randomness without classical communication. This model is stronger than the biseparable model and implies new genuinely multipartite entanglement. With the present local model it is proved that all the permutationally symmetric entangled pure states are new genuinely multipartite entanglement. It is further proved that the new feature holds for all the multipartite entangled pure states in the biseparable model with the dimensions of local systems being not larger than three. The new multipartite entanglement is also robust against general noises. Finally, a simple Bell inequality is provided to verify new genuinely multipartite entangled pure qubit states in the present model. The results show new insight into featuring the genuinely multipartite entanglement in the distributive scenarios.
The quantum entanglement as one of very important resources has been widely used in quantum information processing. In this work, we present a new kind of genuine multipartite entanglement. It is derived from special geometric feature of entangled systems compared with quantum multisource networks. We prove that any symmetric entangled pure state shows stronger nonlocality than the genuinely multipartite nonlocality in the biseparable model. Similar results hold for other entangled pure states with local dimensions no larger than 333. We further provide computational conditions for witnessing the new nonlocality of noisy states. These results suggest that the present model is useful characterizing a new kind of generic quantum entanglement.
Sharing genuine multipartite entanglement by considering collective use of copies of biseparable states, which are entangled across all bipartitions but lack genuine multipartite entanglement at the single-copy level, plays a central role in several quantum information processing protocols, and has been referred as genuine multipartite entanglement activation. We present a protocol for three-qutrit systems showing that two copies of rank-two biseparable states, entangled across every bipartition, are sufficient to generate a genuinely multipartite entangled state with nonzero probability. This contrasts with the three-qubit scenario where many copies of biseparable states might be required for sharing genuine multipartite entanglement. We subsequently generalize our protocols to the case of an arbitrary number of parties. Interestingly, the proposed construction naturally leads to the activation of genuinely nonlocal correlations, yielding a result that is stronger than genuine multipartite entanglement activation alone.
Abstract It remains an open question whether every pure multipartite state that is genuinely entangled is also genuinely nonlocal. Recently, a new general construction of Bell inequalities allowing the detection of genuine multipartite nonlocality (GMNL) in quantum states was proposed in Curchod et al (2019 New J. Phys. 21 023016) with the aim of addressing the above problem. Here we show how, in a simple manner, one can improve this construction to deliver finer Bell inequalities for detection of GMNL. Remarkably, we then prove one of the improved Bell inequalities to be powerful enough to detect GMNL in every three-qubit genuinely entangled state. We also generalize some of these inequalities to detect not only GMNL but also nonlocality depth in multipartite states and we present a possible way of generalizing them to the case of more outcomes.
Genuine multipartite nonlocality and nonlocality arising in networks composed of several independent sources have been separately investigated. While some genuinely entangled states cannot be verified by violating a single Bell-type inequality, a quantum network consisting of different sources allows for the certification of the non-classicality of all sources. In this paper, we propose the first method to verify both types of nonlocality simultaneously in a single experiment. We consider a quantum network comprising a bipartite source and a tripartite source. We demonstrate that there are quantum correlations cannot be simulated if the tripartite source distributes biseparable systems while the bipartite source distributes even stronger-than-quantum systems. These correlations can be used to verify both the genuine multipartite nonlocality of generalized Greenberger-Horne-Zeilinger states and the full network nonlocality that is stronger than all the existing results. Experimentally, we observe both types of nonlocality in a high fidelity photonic quantum network by violating a single network Bell inequality.
Genuine multipartite nonlocality and nonlocality arising in networks composed of several independent sources have been investigated separately. While some genuinely entangled states cannot be verified by violating a single Bell-type inequality, a quantum network consisting of different sources enables the certification of the nonclassicality of all sources. In this Letter, we propose the first method to verify both types of nonlocality simultaneously in a single experiment. We consider a quantum network comprising a bipartite source and a tripartite source. We demonstrate that there are quantum correlations that cannot be simulated if the tripartite source distributes biseparable systems while the bipartite source distributes even stronger-than-quantum systems. These correlations can be used to verify both the genuine multipartite nonlocality of generalized Greenberger-Horne-Zeilinger states and the full network nonlocality that is stronger than all the existing results. Experimentally, we observe both types of nonlocality in a high-fidelity photonic quantum network by violating a single network Bell inequality.
Understanding the relation between nonlocality and entanglement is one of the fundamental problems in quantum physics. In the bipartite case, it is known that these two phenomena are inequivalent, as there exist entangled states of two parties that do not violate any Bell inequality. However, except for a single example of an entangled three-qubit state that has a local model, almost nothing is known about such a relation in multipartite systems. We provide a general construction of genuinely multipartite entangled states that do not display genuinely multipartite nonlocality, thus proving that entanglement and nonlocality are inequivalent for any number of parties.