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:2602.16280

Tomographically-nonlocal entanglement

Roberto D. Baldijão, Marco Erba, David Schmid, John H. Selby, Ana Belén Sainz

quant-phSubmitted Feb 18, 2026• Announced Feb 19, 2026• 0 citations
arXivHTMLPDF

Abstract

Entanglement is a central and subtle feature of quantum theory, whose structure and operational behavior can change dramatically when additional physical constraints, such as symmetries or superselection rules, are imposed. Such constraints can give rise to striking and counter-intuitive phenomena, including local broadcasting of entangled states and failures of entanglement monogamy. These effects naturally arise in tomographically nonlocal theories (like real quantum theory, twirled worlds, or fermionic quantum theory), where composite systems possess holistic degrees of freedom that are inaccessible to local measurements. In this work, we study entanglement in such theories within the framework of generalized probabilistic theories. We show that the failure of tomographic locality leads to two qualitatively distinct forms of entanglement, which we term $\textit{tomographically-local}$ entanglement and $\textit{tomographically-nonlocal}$ entanglement. We analyze the operational consequences of this distinction, proving that tomographically-nonlocal entanglement is useless for Bell nonlocality, steering, and teleportation, but sufficient for dense coding and perfectly secure data hiding. This framework clarifies the origin of several previously puzzling features of entanglement that arise when tomographic locality fails, as can happen even in quantum theory when one considers fermions or fundamental superselection rules.

Comments
29+8 pages, lots of diagrams

Related papers

Experimental Test of the Principle of Tomographic Locality

Tristan S. Lismer, Kaleb B Felefele, Robert W. Spekkens +1 more

The principle of tomographic locality states that the operational state of a multipartite system can be fully characterized by the statistics obtained from measurements that are local to the individual subsystems. This property holds in quantum theory and features prominently in axiomatic reconstructions of the theory, where it serves to rule out a wide class of alternatives. For instance, quantum theory with Hilbert spaces defined over the real field (rather than the complex field) is an example of a theory that is ruled out in this fashion. Given its foundational importance, it is worthwhile to subject this principle to a direct experimental test. Specifically, we consider an experiment on the polarization degrees of freedom of a pair of photonic modes in a prepare-and-measure scenario and analyze the resulting data within the framework of generalized probabilistic theories. The signature of a failure of tomographic locality is that there are pairs of states on the bipartite system that can only be distinguished by the statistics they yield for non-separable measurements. In the full quantum setting, we find no evidence of a violation of tomographic locality. As a test of our analysis method, we also verify that if we restrict attention to those states and measurements that lie within the fragment described by quantum theory over the real field, then a clear signature of the failure of tomographic locality is observed.

arXiv:2506.07775•Jun 9, 2025•0 citations

All Entangled States are Nonlocal and Self-Testable in the Broadcast Scenario

Pavel Sekatski, Jef Pauwels

Entanglement and Bell nonlocality are known to be inequivalent: there exist entangled states that admit a local hidden-variable model for all local measurements. Here we show that this gap disappears in a minimal broadcast extension of the Bell scenario. Assuming only the validity of quantum theory, we prove that for every entangled state $ρ_{AB}$ there exist local broadcasting maps and local measurements such that the resulting four--partite correlations cannot be reproduced by any broadcast network whose source is separable across the $A|B$ cut. Thus, all entangled states are broadcast nonlocal in quantum theory. In addition, we show that all (also mixed) multipartite states can be broadcast-self-tested, according to a natural operational definition.

quant-pharXiv:2512.15656•Dec 18, 2025•0 citations

Quantum Nonseparability Without Nonlocality: A ψ-Ontic Holistic Account of Entangled Measurement

Everett X. Wang

The standard interpretation of quantum measurement on entangled systems holds that measuring one particle nonlocally collapses the wavefunction of its spacelike-separated partner. We argue that this conclusion rests on a false presupposition: that subsystems of entangled systems possess independent ontic states. If the global wavefunction is the sole ontic object (ψ-ontic holism), then for entangled systems, there is no "state of B" to be affected by measurement at A. Measurement is a local dynamical process-concretely modeled by continuous spontaneous localization-that destroys one local wavefunction component at the measurement site; the global state factorizes as a consequence, and subsystem ontology emerges for the first time. The transition of the distant particle's reduced density matrix from mixed to pure reflects this emergence of separability, not a physical change at the distant location. The framework satisfies no-signaling and embraces the contextuality required by the Kochen-Specker and GHZ theorems. We are explicit about its relation to Bell's theorem: Bell local causality (factorizability) fails, as it must in any empirically adequate theory, but the failure is confined to outcome independence and is identified with the nonseparability of the global ontic state, while parameter independence-and with it the locality of the dynamics-holds exactly. Decoherence provides the mechanism by which the global wavefunction factorizes and classical separability emerges. The apparent nonlocality of quantum mechanics is thus reinterpreted as nonseparability: the fundamental ontology is holistic, but the dynamics are local.

Entropy•Sep 9, 2026•0 citations

Bell nonlocality from compatibility of entanglement-breaking channels

Gelo Noel M. Tabia, Chung-Yun Hsieh, Min-Hsiu Hsieh

Locally classical behavior is often interpreted as evidence that a global classical description should exist. In particular, when individual processes admit classical (measure-and-prepare) realizations, it is natural to expect at least one compatible joint implementation that remains classical. We show that this intuition fails in a simple broadcast setting with one input system and two outputs. Specifically, we construct pairs of compatible channels that are entanglement-breaking individually and thus admit classical descriptions, yet every joint broadcast realization is necessarily Bell-nonlocal between the outputs, even for a maximally mixed input. This establishes a form of compatibility-induced activation of nonlocality: Bell nonlocality arises not from entanglement in the inputs or marginal channels, but solely from the requirement that these marginals admit a common global implementation. In this sense, compatibility is not merely a consistency condition on local descriptions, but a mechanism that can enforce nonclassical correlations at the global level.

arXiv:2410.13499•Oct 17, 2024•0 citations

Quantum Nonseparability Without Nonlocality: A ψ-Ontic Holistic Account of Entangled Measurement

Everett X. Wang

The standard interpretation of quantum measurement on entangled systems holds that measuring one particle nonlocally collapses the wavefunction of its spacelike-separated partner. We argue that this conclusion rests on a false presupposition: that subsystems of entangled systems possess independent ontic states. If the global wavefunction is the sole ontic object (ψ-ontic holism), then for entangled systems there is no “state of B” to be affected by measurement at A. The reduced density matrix of a subsystem, while operationally useful, is not ontologically real for non-factorizable states. Measurement is a local dynamical process — concretely modeled by continuous spontaneous localization (CSL) — that destroys one local wavefunction component at the measurement site. The global state factorizes as a consequence, and subsystem ontology emerges for the first time. The transition of the distant particle’s reduced density matrix from mixed to pure reflects this emergence of separability, not a physical change at the distant location. We show that this framework is consistent with no-signaling, with the contextuality required by the Kochen–Specker and GHZ theorems, and with the local measurement axiom (Postulate M) proposed in a companion paper. Bell’s theorem does not force nonlocality upon our framework because it presupposes outcome determinism — the assignment of definite values to observables prior to measurement — which several quantum mechanical theorems and our ψ-ontic ontology explicitly deny. Decoherence, which is ubiquitous in nature, provides the mechanism by which the global wavefunction factorizes and classical separability emerges. The apparent nonlocality of quantum mechanics is thus reinterpreted as nonseparability: the fundamental ontology is holistic, but the dynamics are local.

•Jun 8, 2026•0 citations

The Complete Disenchantment of Quantum Entanglement

Jiwen Nie

The Complete Disenchantment of Quantum Entanglement—Failure of Measurement Independence and a Field-Theoretic Explanation of Electron Internal Structure This paper provides a physical explanation of quantum entanglement—the most central puzzle in quantum mechanics—without relying on "nonlocality." The violation of Bell's inequality is widely interpreted by mainstream physics as "experimental falsification of local realism," from which the conclusion "the world is nonlocal" is drawn. This paper points out that this chain of reasoning depends on a premise that has never been independently tested: the measurement process does not change the hidden variable that determines the measurement outcome. This theory divides all matter in the universe into Nie-matter entities (massive, Staticity) and Ji-matter entities (massless, Dynamicity). The electron is not a point particle, but a Nie-matter entity composed of Zhonghua Micro-Particles, possessing an internal Ji-matter field configuration (the electron self-field). When a measurement device operates, it inevitably releases a Ji-matter field; this field undergoes local coupling with the electron self-field, changing the electron's effective configuration from the original configuration λ₀ at production to the coupled effective configuration λ_eff(a) = C[λ₀, F_device(a)]. The measurement outcome is a function of λ_eff(a), not a function of λ₀ alone—therefore, the measurement-independence premise of Bell's theorem does not hold physically. This paper further argues: the electron's having internal structure is precisely the physical origin of the angle-dependent correlations. If the electron were an unstructured point particle, measurements at different angles should give the same result—but experiments observe angle-dependent correlations, which in itself already proves that the electron is not a point particle. Bell-inequality experiments have never been a "victory of nonlocality"—they are ironclad evidence that the electron has internal structure. This paper gives four core arguments: P6-4C (failure of the premises of Bell's inequality derivation), P6-4D (change of electron state by the measurement device's Ji-matter field), P6-5 (how a point particle absorbs a photon—the electron must have internal structure to accommodate an absorbed photon), P6-4A (Bell's inequality—ironclad evidence that the electron has internal structure), and P6-4B (local mechanism of Bell experiments and experimental test paths for electron internal structure). These include an order-of-magnitude estimate of the electron internal structure correction to g-2 (~10⁻¹⁸), a comparison with current experimental precision (~10⁻¹²), and future test paths. The full text does not claim that Bell's inequality is "overturned"—it is a mathematically correct theorem. What this paper claims is: the measurement-independence premise on which Bell's inequality depends does not hold under the physical picture in which measurement is local field coupling. Violating Bell's inequality is precisely evidence that the electron has an internal Ji-matter field configuration, not evidence for nonlocality.

•Oct 21, 2026•0 citations
Entanglement is a central and subtle feature of quantum theory, whose structure and operational behavior can change dramatically when additional physical constraints, such as symmetries or superselection rules, are imposed. Such constraints can give rise to striking and counter-intuitive phenomena, including local broadcasting of entangled states and failures of entanglement monogamy. These effects naturally arise in tomographically nonlocal theories (like real quantum theory, twirled worlds, or fermionic quantum theory), where composite systems possess holistic degrees of freedom that are inaccessible to local measurements. In this work, we study entanglement in such theories within the framework of generalized probabilistic theories. We show that the failure of tomographic locality leads to two qualitatively distinct forms of entanglement, which we term tomographically-local\textit{tomographically-local}tomographically-local entanglement and tomographically-nonlocal\textit{tomographically-nonlocal}tomographically-nonlocal entanglement. We analyze the operational consequences of this distinction, proving that tomographically-nonlocal entanglement is useless for Bell nonlocality, steering, and teleportation, but sufficient for dense coding and perfectly secure data hiding. This framework clarifies the origin of several previously puzzling features of entanglement that arise when tomographic locality fails, as can happen even in quantum theory when one considers fermions or fundamental superselection rules.
The principle of tomographic locality states that the operational state of a multipartite system can be fully characterized by the statistics obtained from measurements that are local to the individual subsystems. This property holds in quantum theory and features prominently in axiomatic reconstructions of the theory, where it serves to rule out a wide class of alternatives. For instance, quantum theory with Hilbert spaces defined over the real field (rather than the complex field) is an example of a theory that is ruled out in this fashion. Given its foundational importance, it is worthwhile to subject this principle to a direct experimental test. Specifically, we consider an experiment on the polarization degrees of freedom of a pair of photonic modes in a prepare-and-measure scenario and analyze the resulting data within the framework of generalized probabilistic theories. The signature of a failure of tomographic locality is that there are pairs of states on the bipartite system that can only be distinguished by the statistics they yield for non-separable measurements. In the full quantum setting, we find no evidence of a violation of tomographic locality. As a test of our analysis method, we also verify that if we restrict attention to those states and measurements that lie within the fragment described by quantum theory over the real field, then a clear signature of the failure of tomographic locality is observed.
Entanglement and Bell nonlocality are known to be inequivalent: there exist entangled states that admit a local hidden-variable model for all local measurements. Here we show that this gap disappears in a minimal broadcast extension of the Bell scenario. Assuming only the validity of quantum theory, we prove that for every entangled state ρABρ_{AB}ρAB​ there exist local broadcasting maps and local measurements such that the resulting four--partite correlations cannot be reproduced by any broadcast network whose source is separable across the A∣BA|BA∣B cut. Thus, all entangled states are broadcast nonlocal in quantum theory. In addition, we show that all (also mixed) multipartite states can be broadcast-self-tested, according to a natural operational definition.
The standard interpretation of quantum measurement on entangled systems holds that measuring one particle nonlocally collapses the wavefunction of its spacelike-separated partner. We argue that this conclusion rests on a false presupposition: that subsystems of entangled systems possess independent ontic states. If the global wavefunction is the sole ontic object (ψ-ontic holism), then for entangled systems, there is no "state of B" to be affected by measurement at A. Measurement is a local dynamical process-concretely modeled by continuous spontaneous localization-that destroys one local wavefunction component at the measurement site; the global state factorizes as a consequence, and subsystem ontology emerges for the first time. The transition of the distant particle's reduced density matrix from mixed to pure reflects this emergence of separability, not a physical change at the distant location. The framework satisfies no-signaling and embraces the contextuality required by the Kochen-Specker and GHZ theorems. We are explicit about its relation to Bell's theorem: Bell local causality (factorizability) fails, as it must in any empirically adequate theory, but the failure is confined to outcome independence and is identified with the nonseparability of the global ontic state, while parameter independence-and with it the locality of the dynamics-holds exactly. Decoherence provides the mechanism by which the global wavefunction factorizes and classical separability emerges. The apparent nonlocality of quantum mechanics is thus reinterpreted as nonseparability: the fundamental ontology is holistic, but the dynamics are local.
Locally classical behavior is often interpreted as evidence that a global classical description should exist. In particular, when individual processes admit classical (measure-and-prepare) realizations, it is natural to expect at least one compatible joint implementation that remains classical. We show that this intuition fails in a simple broadcast setting with one input system and two outputs. Specifically, we construct pairs of compatible channels that are entanglement-breaking individually and thus admit classical descriptions, yet every joint broadcast realization is necessarily Bell-nonlocal between the outputs, even for a maximally mixed input. This establishes a form of compatibility-induced activation of nonlocality: Bell nonlocality arises not from entanglement in the inputs or marginal channels, but solely from the requirement that these marginals admit a common global implementation. In this sense, compatibility is not merely a consistency condition on local descriptions, but a mechanism that can enforce nonclassical correlations at the global level.
The standard interpretation of quantum measurement on entangled systems holds that measuring one particle nonlocally collapses the wavefunction of its spacelike-separated partner. We argue that this conclusion rests on a false presupposition: that subsystems of entangled systems possess independent ontic states. If the global wavefunction is the sole ontic object (ψ-ontic holism), then for entangled systems there is no “state of B” to be affected by measurement at A. The reduced density matrix of a subsystem, while operationally useful, is not ontologically real for non-factorizable states. Measurement is a local dynamical process — concretely modeled by continuous spontaneous localization (CSL) — that destroys one local wavefunction component at the measurement site. The global state factorizes as a consequence, and subsystem ontology emerges for the first time. The transition of the distant particle’s reduced density matrix from mixed to pure reflects this emergence of separability, not a physical change at the distant location. We show that this framework is consistent with no-signaling, with the contextuality required by the Kochen–Specker and GHZ theorems, and with the local measurement axiom (Postulate M) proposed in a companion paper. Bell’s theorem does not force nonlocality upon our framework because it presupposes outcome determinism — the assignment of definite values to observables prior to measurement — which several quantum mechanical theorems and our ψ-ontic ontology explicitly deny. Decoherence, which is ubiquitous in nature, provides the mechanism by which the global wavefunction factorizes and classical separability emerges. The apparent nonlocality of quantum mechanics is thus reinterpreted as nonseparability: the fundamental ontology is holistic, but the dynamics are local.
The Complete Disenchantment of Quantum Entanglement—Failure of Measurement Independence and a Field-Theoretic Explanation of Electron Internal Structure This paper provides a physical explanation of quantum entanglement—the most central puzzle in quantum mechanics—without relying on "nonlocality." The violation of Bell's inequality is widely interpreted by mainstream physics as "experimental falsification of local realism," from which the conclusion "the world is nonlocal" is drawn. This paper points out that this chain of reasoning depends on a premise that has never been independently tested: the measurement process does not change the hidden variable that determines the measurement outcome. This theory divides all matter in the universe into Nie-matter entities (massive, Staticity) and Ji-matter entities (massless, Dynamicity). The electron is not a point particle, but a Nie-matter entity composed of Zhonghua Micro-Particles, possessing an internal Ji-matter field configuration (the electron self-field). When a measurement device operates, it inevitably releases a Ji-matter field; this field undergoes local coupling with the electron self-field, changing the electron's effective configuration from the original configuration λ₀ at production to the coupled effective configuration λ_eff(a) = C[λ₀, F_device(a)]. The measurement outcome is a function of λ_eff(a), not a function of λ₀ alone—therefore, the measurement-independence premise of Bell's theorem does not hold physically. This paper further argues: the electron's having internal structure is precisely the physical origin of the angle-dependent correlations. If the electron were an unstructured point particle, measurements at different angles should give the same result—but experiments observe angle-dependent correlations, which in itself already proves that the electron is not a point particle. Bell-inequality experiments have never been a "victory of nonlocality"—they are ironclad evidence that the electron has internal structure. This paper gives four core arguments: P6-4C (failure of the premises of Bell's inequality derivation), P6-4D (change of electron state by the measurement device's Ji-matter field), P6-5 (how a point particle absorbs a photon—the electron must have internal structure to accommodate an absorbed photon), P6-4A (Bell's inequality—ironclad evidence that the electron has internal structure), and P6-4B (local mechanism of Bell experiments and experimental test paths for electron internal structure). These include an order-of-magnitude estimate of the electron internal structure correction to g-2 (~10⁻¹⁸), a comparison with current experimental precision (~10⁻¹²), and future test paths. The full text does not claim that Bell's inequality is "overturned"—it is a mathematically correct theorem. What this paper claims is: the measurement-independence premise on which Bell's inequality depends does not hold under the physical picture in which measurement is local field coupling. Violating Bell's inequality is precisely evidence that the electron has an internal Ji-matter field configuration, not evidence for nonlocality.