In conical spacetimes with d>1, NSS prohibits operationally detectable causal loops across classical, quantum and post-quantum theories, unlike the (1+1) case.
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Quantum correlations with no causal order
13 Pith papers cite this work. Polarity classification is still indexing.
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Pith papers citing it
abstract
The idea that events obey a definite causal order is deeply rooted in our understanding of the world and at the basis of the very notion of time. But where does causal order come from, and is it a necessary property of nature? We address these questions from the standpoint of quantum mechanics in a new framework for multipartite correlations which does not assume a pre-defined global causal structure but only the validity of quantum mechanics locally. All known situations that respect causal order, including space-like and time-like separated experiments, are captured by this framework in a unified way. Surprisingly, we find correlations that cannot be understood in terms of definite causal order. These correlations violate a 'causal inequality' that is satisfied by all space-like and time-like correlations. We further show that in a classical limit causal order always arises, which suggests that space-time may emerge from a more fundamental structure in a quantum-to-classical transition.
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Introduces essential unitarity as the unique structure-compatible generalization of unitarity to higher-order quantum interfaces in a categorical framework, with all quantum core morphisms satisfying it.
Necessary and sufficient conditions combining directional conditional independence, positivity of the pseudo-density matrix, and an algebraic consistency requirement for identifying memoryless sequential quantum processes from restricted projective data.
Presents a poly-complexity quantum circuit implementing the random dilation superchannel for parallel channel queries, with approximate sequential extension, a no-go theorem for exact sequential dilation, and an application to exponentially improved channel storage-retrieval.
Quantum strategy stores isometry channels with n = Θ(1/√ε) queries for error ε, quadratic improvement over classical n = Θ(ε^{-1}).
First experimental implementation of a device-independent inequality violation for indefinite causal order, with measured value 1.8328 ± 0.0045 against bound 1.75.
Defines polyslot pslot[C] and srep[C] constructions on symmetric monoidal categories that reconstruct unitary supermaps and forbid time-loops in composition, with equivalence shown on path-contraction groupoids.
The authors experimentally demonstrate time-delocalized local measurements inside a photonic quantum switch that preserve indefinite causal order, achieving a causal witness value of C_W ≈ -0.305(1).
Higher-order quantum map types form a distributive lattice of regular subtypes where signalling relations are determined by type function evaluations and structure poset rank parity, with normal forms derived from maximal chains.
Quantum matter sources an operator-valued Shapiro delay that promotes causal boundaries to noncommuting observables and allows superpositions of causal relations between spacetime points.
Optimal bounds on multipartite nonlocality for threshold games are derived via a reduction to biased bipartite nonlocality in the LOCCG model.
In bipartite processes and multipartite quantum circuits with quantum control, causal nonseparability persists when any single non-future system remains undephased but becomes separable if all systems or only the future system is undephased.
Temporal state tomography reconstructs multi-time quantum processes from temporal quasiprobability distributions via a Bloch-type representation and derives the associated sample complexity.
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Impossibility of superluminal signalling rules out causal loops in conical spacetimes
In conical spacetimes with d>1, NSS prohibits operationally detectable causal loops across classical, quantum and post-quantum theories, unlike the (1+1) case.
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Essential Unitarity for Higher-Order Quantum Computation
Introduces essential unitarity as the unique structure-compatible generalization of unitarity to higher-order quantum interfaces in a categorical framework, with all quantum core morphisms satisfying it.
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Causal-Order Identification of Memoryless Sequential Quantum Processes from Restricted Projective Data
Necessary and sufficient conditions combining directional conditional independence, positivity of the pseudo-density matrix, and an algebraic consistency requirement for identifying memoryless sequential quantum processes from restricted projective data.
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Random dilation superchannel
Presents a poly-complexity quantum circuit implementing the random dilation superchannel for parallel channel queries, with approximate sequential extension, a no-go theorem for exact sequential dilation, and an application to exponentially improved channel storage-retrieval.
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Quantum Advantage in Storage and Retrieval of Isometry Channels
Quantum strategy stores isometry channels with n = Θ(1/√ε) queries for error ε, quadratic improvement over classical n = Θ(ε^{-1}).
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Toward an Experimental Device-Independent Verification of Indefinite Causal Order
First experimental implementation of a device-independent inequality violation for indefinite causal order, with measured value 1.8328 ± 0.0045 against bound 1.75.
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Polycategorical Constructions for Unitary Supermaps of Arbitrary Dimension
Defines polyslot pslot[C] and srep[C] constructions on symmetric monoidal categories that reconstruct unitary supermaps and forbid time-loops in composition, with equivalence shown on path-contraction groupoids.
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Time-Delocalized Local Measurements in an Indefinite Causal Order
The authors experimentally demonstrate time-delocalized local measurements inside a photonic quantum switch that preserve indefinite causal order, achieving a causal witness value of C_W ≈ -0.305(1).
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Order structure and signalling in higher order quantum maps
Higher-order quantum map types form a distributive lattice of regular subtypes where signalling relations are determined by type function evaluations and structure poset rank parity, with normal forms derived from maximal chains.
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Quantum matter sources an operator-valued Shapiro delay that promotes causal boundaries to noncommuting observables and allows superpositions of causal relations between spacetime points.
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Bounds on Multipartite Nonlocality via Reduction to Biased Nonlocality
Optimal bounds on multipartite nonlocality for threshold games are derived via a reduction to biased bipartite nonlocality in the LOCCG model.
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In bipartite processes and multipartite quantum circuits with quantum control, causal nonseparability persists when any single non-future system remains undephased but becomes separable if all systems or only the future system is undephased.
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Temporal State Tomography via Quantum Snapshotting the Temporal Quasiprobabilities
Temporal state tomography reconstructs multi-time quantum processes from temporal quasiprobability distributions via a Bloch-type representation and derives the associated sample complexity.