Experimental violation of n-locality in a star quantum network

Poderini, Davide; Agresti, Iris; Marchese, Guglielmo; Polino, Emanuele; Giordani, Taira; Suprano, Alessia; Valeri, Mauro; Milani, Giorgio; Spagnolo, Nicolò; Carvacho, Gonzalo; Chaves, Rafael; Sciarrino, Fabio

doi:10.1038/s41467-020-16189-6

Cited by 60 publications

(46 citation statements)

References 53 publications

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“…where I t ≔ ð1=2 n Þ P ā;x;b ð−1Þ a 1 þÁÁÁþa n þt•bþt•x pð ā; bjxÞ, the n-bit strings t and t are t ¼ ð1; t 1 ; t 2 ; …Þ and t ¼ ð⨁ n−1 k¼1 t k ; t 1 ; t 2 ; …Þ, and ðt 1 ; t 2 ; …Þ is the string of n − 1 bits representing t. The best known quantum protocol achieves S n ¼ ffiffi ffi 2 p by having each source emitting the singlet state jψ − i, the central party performing a joint nqubit entanglement swapping measurement, and letting the branch parties measure suitable anticommuting observables [31]. The inequality (or modifications of it) has been violated in experiments using complete entanglement swapping [32] and separable measurements [33].…”

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confidence: 99%

Full Network Nonlocality

2022

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Networks have advanced the study of nonlocality beyond Bell's theorem. Here, we introduce the concept of full network nonlocality, which describes correlations that necessitate all links in a network to distribute nonlocal resources. Showcasing that this notion is stronger than standard network nonlocality, we prove that the most well-known network Bell test does not witness full network nonlocality. In contrast, we demonstrate that its generalization to star networks is capable of detecting full network nonlocality in quantum theory. More generally, we point out that established methods for analyzing local and theoryindependent correlations in networks can be combined in order to systematically deduce sufficient conditions for full network nonlocality in any network and input-output scenario. We demonstrate the usefulness of these methods by constructing polynomial witnesses of full network nonlocality for the bilocal scenario. Then, we show that these inequalities can be violated via quantum elegant joint measurements.

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confidence: 99%

Full Network Nonlocality

2022

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“…Each source distributes a state to one of the n edge parties (Alices) and the central party (Bob). Experimental tests of the bilocality inequality [37][38][39][40] and the n-locality inequalities in starnetwork configuration [41] have also been reported. The nlocality in the star-network scenario is commonly studied for two binary-outcome observables (say, m = 2) per party.…”

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confidence: 99%

Generalized $n$-locality inequalities in star-network configuration and their optimal quantum violations

Munshi,

Pan

2021

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Network Bell experiments reveal a form of nonlocality conceptually different from standard Bell nonlocality. Standard multiparty Bell experiments involve a single source shared by a set of observers. In contrast, network Bell experiments feature multiple independent sources, and each of them may distribute physical systems to a set of observers who perform randomly chosen measurements. The n-locality scenario in star-network configuration involves n number of edge observers (Alices), a central observer (Bob), and n number of independent sources having no prior correlation. Each Alice shares an independent state with the central observer Bob. Usually, in network Bell experiments, one considers that each party measures only two observables. In this work, we propose a non-trivial generalization of n-locality scenario in star-network configuration, where each Alice performs some integer m number of binary-outcome measurements, and the central party Bob performs 2 m−1 binary-outcome measurements. We derive a family of generalized n-locality inequalities for any arbitrary m. Using bluean elegant sum-of-squares approach, we derive the optimal quantum violation of the aforementioned inequalities can be attained when each and every Alice measures m number of mutually anticommuting observables. For m = 2 and 3, one obtains the optimal quantum value bluefor qubit system local to each Alice, and it is sufficient to consider the sharing of a two-qubit entangled state between each Alice and Bob. We further demonstrate that the optimal quantum violation of n-locality inequality for any arbitrary m can be obtained when every Alice shares m/2 copies of two-qubit maximally entangled state with the central party Bob. We also argue that for m > 3, a single copy of a two-qubit entangled state may not be enough to exhibit the violation of n-locality inequality but multiple copies of it can activate the quantum violation. We discuss the implications of our study and raise some open questions.

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“…In spite of its clear foundational and technological relevance, however, the experimental investigation of these new forms of nonlocality [61][62][63][64][65][66][67][68][69][70] have been hampered by difficulties arising from quantum networks. Indeed, in order to realize large scale quantum networks and exploit them for practical tasks [4,71], it is crucial to extend their implementation to urban scale scenarios.…”

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confidence: 99%

“…In this work, we take a significant step in this direction, by experimentally realizing a bilocal network [47,48,61,[63][64][65], a scenario akin to the paradigmatic entanglement swapping protocol [72,73]. Importantly, differently from previous experiments, we generate nonlocal correlations in this network through a scalable and hybrid photonic platform composed of two photonic sources distributing photons among three nodes.…”

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confidence: 99%

“…Moving beyond this simple causal structure, it has been realized that networks of different topologies involving an increasing number of nodes and independent sources can lead to new forms of nonlocality [48,[50][51][52][53][54][55][56][57][58][59][60], motivating a number of novel experimental implementations [61][62][63][64][65][66][67][68][69][70]. Of particular, relevance is the bilocality scenario, providing the simplest network beyond the bipartite case and that for this reason has attract significant interest [47][48][49][50][61][62][63][64][65]. Its causal structure is represented by the DAG in Fig.…”

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Quantum violation of local causality in urban network with hybrid photonic technologies

Carvacho¹,

Roccia²,

Valeri³

et al. 2021

Preprint

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Quantum networks play a crucial role for distributed quantum information processing, enabling the establishment of entanglement and quantum communication among distant nodes. Fundamentally, networks with independent sources allow for new forms of nonlocality, beyond the paradigmatic Bell's theorem. Here we implement the simplest of such networks -the bilocality scenario-in an urban network connecting different buildings with a fully scalable and hybrid approach. Two independent sources using different technologies, respectively a quantum dot and a nonlinear crystal, are used to share photonic entangled state among three nodes connected through a 270 m free-space channel and fiber links. By violating a suitable non-linear Bell inequality, we demonstrate the nonlocal behaviour of the correlations among the nodes of the network. Our results pave the way towards the realization of more complex networks and the implementation of quantum communication protocols in an urban environment, leveraging on the capabilities of hybrid photonic technologies.

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Experimental violation of n-locality in a star quantum network

Cited by 60 publications

References 53 publications

Full Network Nonlocality

Full Network Nonlocality

Generalized $n$-locality inequalities in star-network configuration and their optimal quantum violations

Quantum violation of local causality in urban network with hybrid photonic technologies

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