Challenges
Datasets
Workspaces
Papers
Discussions
Leaderboard
Log inSign up
Challenges
Datasets
Workspaces
Papers
Discussions
Leaderboard
Blog
Job Board
Q3AS

© 2026 Aqora Quantum S.A.S.

TermsPrivacyLegal Notice

arXiv:1402.3992 · Physical Review A

Certifying nonlocality from separable marginals

Tamás Vértesi, Wiesław Laskowski, Károly F. Pál

Published Jan 17, 2014• 8 citations
arXivHTMLPDF

Abstract

Imagine three parties, Alice, Bob, and Charlie, who share a state of three qubits such that all two-party reduced states $A$-$B$, $A$-$C$, and $B$-$C$ are separable. Suppose that they have information only about these marginals but not about the global state. According to recent results, there exists an example for a set of three separable two-party reduced states that is only compatible with an entangled global state. In this paper, we show a stronger result by exhibiting separable two-party reduced states $A$-$B$, $A$-$C$, and $B$-$C$, such that any global state compatible with these marginals is nonlocal. Hence, we obtain that nonlocality of multipartite states can be certified from information only about separable marginals.

DOI
10.1103/physreva.89.012115

Related papers

Nonlocal multipartite correlations from local marginal probabilities

Lars Erik Würflinger, Jean-Daniel Bancal, Antonio Acín +2 more

Understanding what can be inferred about a multiparticle quantum system given only the knowledge of its subparts is a highly nontrivial task. Clearly, if a global system does not contain an information resource of some kind, neither do its subparts. For the case of entanglement as an information resource, it is known that the converse of this last statement is not true: Some nonentangled reduced states are only compatible with global states which are entangled. We extend this result to correlations and provide local marginal correlations that are only compatible with global genuinely tripartite nonlocal correlations. Quantum nonlocality can thus be deduced from the mere observation of local marginal correlations.

arXiv:1203.4968•Physical Review A•Sep 20, 2012•31 citations

Self-testing using only marginal information

Xinhui Li, Yu Cai, Yun-Guang Han +2 more

The partial states of a multipartite quantum state may carry a lot of information: in some cases, they determine the global state uniquely. This result is known for tomographic information, that is for fully characterized measurements. We extend it to the device-independent framework by exhibiting sets of two-party correlations that self-test pure three-qubit states.

arXiv:1808.02223•Physical Review A•Nov 26, 2018•14 citations

Entanglement transitivity problems

Gelo Noel M. Tabia, Kai-Siang Chen, Chung-Yun Hsieh +2 more

Abstract One of the goals of science is to understand the relation between a whole and its parts, as exemplified by the problem of certifying the entanglement of a system from the knowledge of its reduced states. Here, we focus on a different but related question: can a collection of marginal information reveal new marginal information? We answer this affirmatively and show that (non-) entangled marginal states may exhibit (meta)transitivity of entanglement, i.e., implying that a different target marginal must be entangled. By showing that the global n -qubit state compatible with certain two-qubit marginals in a tree form is unique, we prove that transitivity exists for a system involving an arbitrarily large number of qubits. We also completely characterize—in the sense of providing both the necessary and sufficient conditions—when (meta)transitivity can occur in a tripartite scenario when the two-qudit marginals given are either the Werner states or the isotropic states. Our numerical results suggest that in the tripartite scenario, entanglement transitivity is generic among the marginals derived from pure states.

arXiv:2203.08023•npj Quantum Information•Aug 25, 2022•11 citations

Nonlocality of quantum states can be transitive

Kai-Siang Chen, Gelo Noel M. Tabia, Chung-Yun Hsieh +2 more

Abstract Despite the monogamous nature of nonlocal correlations, in a Bell test involving three parties A, B, and C, the nonlocality in two bipartite subsystems (e.g., AB and BC) may force the remaining bipartite subsystem (e.g., AC) to exhibit nonlocality. Although this intriguing effect of nonlocality transitivity has been identified in the non -quantum non-signaling world since 2011, whether such transitivity could manifest within quantum theory has remained unresolved. Here, we answer this open problem affirmatively—both analytically and numerically—at the level of quantum states, thereby showing that a quantum-realizable notion of nonlocality transitivity exists. In our analytic construction, we prove and use the fact that copies of the W -state marginals uniquely determine the global compatible state, thus establishing another instance when the parts determine the whole. Moreover, we present a simple method to construct quantum states and correlations that are nonlocal in all their non-unipartite marginals. We also discuss the implications of our results in (semi-) device-independent cryptographic and certification tasks.

arXiv:2412.10505•npj Quantum Information•Jan 10, 2026•2 citations

Nonlocality under Computational Assumptions

Khashayar Barooti, Alexandru Gheorghiu, Grzegorz Głuch +1 more

Nonlocality and its connections to entanglement are fundamental features of quantum mechanics that have found numerous applications in quantum information science. A set of correlations is said to be nonlocal if it cannot be reproduced by spacelike-separated parties sharing randomness and performing local operations. An important practical consideration is that the runtime of the parties has to be shorter than the time it takes light to travel between them. One way to model this restriction is to assume that the parties are computationally bounded. We therefore initiate the study of nonlocality under computational assumptions and derive the following results: (a) We define the set $\mathsf{NeL}$ (not-efficiently-local) as consisting of all bipartite states whose correlations arising from local measurements cannot be reproduced with shared randomness and \emph{polynomial-time} local operations. (b) Under the assumption that the Learning With Errors problem cannot be solved in \emph{quantum} polynomial-time, we show that $\mathsf{NeL}=\mathsf{ENT}$, where $\mathsf{ENT}$ is the set of \emph{all} bipartite entangled states (pure and mixed). This is in contrast to the standard notion of nonlocality where it is known that some entangled states, e.g. Werner states, are local. In essence, we show that there exist (efficient) local measurements producing correlations that cannot be reproduced through shared randomness and quantum polynomial-time computation. (c) We prove that if $\mathsf{NeL}=\mathsf{ENT}$ unconditionally, then $\mathsf{BQP}\neq\mathsf{PP}$. In other words, the ability to certify all bipartite entangled states against computationally bounded adversaries gives a non-trivial separation of complexity classes. (d) Using (c), we show that a certain natural class of 1-round delegated quantum computation protocols that are sound against $\mathsf{PP}$ provers cannot exist.

arXiv:2303.02080•Mar 3, 2023•0 citations

Compatibility relations between the reduced and global density matrices

Yong‐Jian Han, Y.-S. Zhang, Guang‐Can Guo

It is a hard and important problem to find the criterion of a set of positive-definite matrices which can be written as reduced density operators of a multipartite global quantum state. This problem is closely related to the study of many-body quantum entanglement, which is one of the focuses of current quantum-information theory. We give several results on the necessary compatibility relations between a set of reduced and global density matrices, including (i) compatibility conditions for the one-party reduced density matrices of any $({N}_{A}\ifmmode\times\else\texttimes\fi{}{N}_{B})$-dimensional bipartite mixed quantum state, (ii) compatibility conditions for the one-party reduced matrices of any $M$-partite quantum states with the dimension ${N}^{\ensuremath{\bigotimes}M}$, and (iii) compatibility conditions for the two-party reduced density matrixes of $(2\ifmmode\times\else\texttimes\fi{}2\ifmmode\times\else\texttimes\fi{}2)$-dimensional tripartite mixed quantum state.

Physical Review A•May 5, 2005•13 citations
Imagine three parties, Alice, Bob, and Charlie, who share a state of three qubits such that all two-party reduced states AAA-BBB, AAA-CCC, and BBB-CCC are separable. Suppose that they have information only about these marginals but not about the global state. According to recent results, there exists an example for a set of three separable two-party reduced states that is only compatible with an entangled global state. In this paper, we show a stronger result by exhibiting separable two-party reduced states AAA-BBB, AAA-CCC, and BBB-CCC, such that any global state compatible with these marginals is nonlocal. Hence, we obtain that nonlocality of multipartite states can be certified from information only about separable marginals.
Understanding what can be inferred about a multiparticle quantum system given only the knowledge of its subparts is a highly nontrivial task. Clearly, if a global system does not contain an information resource of some kind, neither do its subparts. For the case of entanglement as an information resource, it is known that the converse of this last statement is not true: Some nonentangled reduced states are only compatible with global states which are entangled. We extend this result to correlations and provide local marginal correlations that are only compatible with global genuinely tripartite nonlocal correlations. Quantum nonlocality can thus be deduced from the mere observation of local marginal correlations.
Abstract One of the goals of science is to understand the relation between a whole and its parts, as exemplified by the problem of certifying the entanglement of a system from the knowledge of its reduced states. Here, we focus on a different but related question: can a collection of marginal information reveal new marginal information? We answer this affirmatively and show that (non-) entangled marginal states may exhibit (meta)transitivity of entanglement, i.e., implying that a different target marginal must be entangled. By showing that the global n -qubit state compatible with certain two-qubit marginals in a tree form is unique, we prove that transitivity exists for a system involving an arbitrarily large number of qubits. We also completely characterize—in the sense of providing both the necessary and sufficient conditions—when (meta)transitivity can occur in a tripartite scenario when the two-qudit marginals given are either the Werner states or the isotropic states. Our numerical results suggest that in the tripartite scenario, entanglement transitivity is generic among the marginals derived from pure states.
Abstract Despite the monogamous nature of nonlocal correlations, in a Bell test involving three parties A, B, and C, the nonlocality in two bipartite subsystems (e.g., AB and BC) may force the remaining bipartite subsystem (e.g., AC) to exhibit nonlocality. Although this intriguing effect of nonlocality transitivity has been identified in the non -quantum non-signaling world since 2011, whether such transitivity could manifest within quantum theory has remained unresolved. Here, we answer this open problem affirmatively—both analytically and numerically—at the level of quantum states, thereby showing that a quantum-realizable notion of nonlocality transitivity exists. In our analytic construction, we prove and use the fact that copies of the W -state marginals uniquely determine the global compatible state, thus establishing another instance when the parts determine the whole. Moreover, we present a simple method to construct quantum states and correlations that are nonlocal in all their non-unipartite marginals. We also discuss the implications of our results in (semi-) device-independent cryptographic and certification tasks.
Nonlocality and its connections to entanglement are fundamental features of quantum mechanics that have found numerous applications in quantum information science. A set of correlations is said to be nonlocal if it cannot be reproduced by spacelike-separated parties sharing randomness and performing local operations. An important practical consideration is that the runtime of the parties has to be shorter than the time it takes light to travel between them. One way to model this restriction is to assume that the parties are computationally bounded. We therefore initiate the study of nonlocality under computational assumptions and derive the following results: (a) We define the set NeL\mathsf{NeL}NeL (not-efficiently-local) as consisting of all bipartite states whose correlations arising from local measurements cannot be reproduced with shared randomness and \emph{polynomial-time} local operations. (b) Under the assumption that the Learning With Errors problem cannot be solved in \emph{quantum} polynomial-time, we show that NeL=ENT\mathsf{NeL}=\mathsf{ENT}NeL=ENT, where ENT\mathsf{ENT}ENT is the set of \emph{all} bipartite entangled states (pure and mixed). This is in contrast to the standard notion of nonlocality where it is known that some entangled states, e.g. Werner states, are local. In essence, we show that there exist (efficient) local measurements producing correlations that cannot be reproduced through shared randomness and quantum polynomial-time computation. (c) We prove that if NeL=ENT\mathsf{NeL}=\mathsf{ENT}NeL=ENT unconditionally, then BQP≠PP\mathsf{BQP}\neq\mathsf{PP}BQP=PP. In other words, the ability to certify all bipartite entangled states against computationally bounded adversaries gives a non-trivial separation of complexity classes. (d) Using (c), we show that a certain natural class of 1-round delegated quantum computation protocols that are sound against PP\mathsf{PP}PP provers cannot exist.
It is a hard and important problem to find the criterion of a set of positive-definite matrices which can be written as reduced density operators of a multipartite global quantum state. This problem is closely related to the study of many-body quantum entanglement, which is one of the focuses of current quantum-information theory. We give several results on the necessary compatibility relations between a set of reduced and global density matrices, including (i) compatibility conditions for the one-party reduced density matrices of any $({N}_{A}\ifmmode\times\else\texttimes\fi{}{N}_{B})$-dimensional bipartite mixed quantum state, (ii) compatibility conditions for the one-party reduced matrices of any MMM-partite quantum states with the dimension ${N}^{\ensuremath{\bigotimes}M}$, and (iii) compatibility conditions for the two-party reduced density matrixes of $(2\ifmmode\times\else\texttimes\fi{}2\ifmmode\times\else\texttimes\fi{}2)$-dimensional tripartite mixed quantum state.