scholarly journals Genuinely multipartite noncausality

Quantum ◽  
2017 ◽  
Vol 1 ◽  
pp. 39 ◽  
Author(s):  
Alastair A. Abbott ◽  
Julian Wechs ◽  
Fabio Costa ◽  
Cyril Branciard
Keyword(s):  
Quantum Mechanics ◽  
Causal Structure ◽  
Matrix Formalism ◽  
Causal Order ◽  
Number Of Parties

The study of correlations with no definite causal order has revealed a rich structure emerging when more than two parties are involved. This motivates the consideration of multipartite "noncausal" correlations that cannot be realised even if noncausal resources are made available to a smaller number of parties. Here we formalise this notion: genuinely N-partite noncausal correlations are those that cannot be produced by grouping N parties into two or more subsets, where a causal order between the subsets exists. We prove that such correlations can be characterised as lying outside a polytope, whose vertices correspond to deterministic strategies and whose facets define what we call "2-causal" inequalities. We show that genuinely multipartite noncausal correlations arise within the process matrix formalism, where quantum mechanics holds locally but no global causal structure is assumed, although for some inequalities no violation was found. We further introduce two refined definitions that allow one to quantify, in different ways, to what extent noncausal correlations correspond to a genuinely multipartite resource.

scholarly journals Time-delocalized quantum subsystems and operations: on the existence of processes with indefinite causal structure in quantum mechanics

Quantum ◽  
2019 ◽  
Vol 3 ◽  
pp. 206 ◽  
Author(s):  
Ognyan Oreshkov
Keyword(s):  
Quantum Mechanics ◽  
Hilbert Spaces ◽  
Coherent Control ◽  
Causal Structure ◽  
Physical Realization ◽  
Causal Order ◽  
Quantum Processes ◽  
Standard Quantum ◽  
Novel Structure ◽  
The Times

It has been shown that it is theoretically possible for there to exist higher-order quantum processes in which the operations performed by separate parties cannot be ascribed a definite causal order. Some of these processes are believed to have a physical realization in standard quantum mechanics via coherent control of the times of the operations. A prominent example is the quantum SWITCH, which was recently demonstrated experimentally. However, the interpretation of such experiments as realizations of a process with indefinite causal structure as opposed to some form of simulation of such a process has remained controversial. Where exactly are the local operations of the parties in such an experiment? On what spaces do they act given that their times are indefinite? Can we probe them directly rather than assume what they ought to be based on heuristic considerations? How can we reconcile the claim that these operations really take place, each once as required, with the fact that the structure of the presumed process implies that they cannot be part of any acyclic circuit? Here, I offer a precise answer to these questions: the input and output systems of the operations in such a process are generally nontrivial subsystems of Hilbert spaces that are tensor products of Hilbert spaces associated with systems at different times---a fact that is directly experimentally verifiable. With respect to these time-delocalized subsystems, the structure of the process is one of a circuit with a causal cycle. This provides a rigorous sense in which processes with indefinite causal structure can be said to exist within the known quantum mechanics. I also identify a whole class of isometric processes, of which the quantum SWITCH is a special case, that admit a physical realization on time-delocalized subsystems. These results unveil a novel structure within quantum mechanics, which may have important implications for physics and information processing.

scholarly journals Beyond Causal Explanation: Einstein’s Principle Not Reichenbach’s

Entropy ◽  
2021 ◽  
Vol 23 (1) ◽  
pp. 114
Author(s):  
Michael Silberstein ◽  
William Mark Stuckey ◽  
Timothy McDevitt
Keyword(s):  
Quantum Mechanics ◽  
Quantum Information ◽  
Causal Explanation ◽  
Causal Structure ◽  
Minkowski Spacetime ◽  
Physical Principle ◽  
Causal Principle ◽  
Complete Rejection ◽  
Epr Correlations ◽  
Tsirelson Bound

Our account provides a local, realist and fully non-causal principle explanation for EPR correlations, contextuality, no-signalling, and the Tsirelson bound. Indeed, the account herein is fully consistent with the causal structure of Minkowski spacetime. We argue that retrocausal accounts of quantum mechanics are problematic precisely because they do not fully transcend the assumption that causal or constructive explanation must always be fundamental. Unlike retrocausal accounts, our principle explanation is a complete rejection of Reichenbach’s Principle. Furthermore, we will argue that the basis for our principle account of quantum mechanics is the physical principle sought by quantum information theorists for their reconstructions of quantum mechanics. Finally, we explain why our account is both fully realist and psi-epistemic.

scholarly journals Cyclic quantum causal models

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Jonathan Barrett ◽  
Robin Lorenz ◽  
Ognyan Oreshkov
Keyword(s):  
Causal Reasoning ◽  
Causal Structure ◽  
Bell Inequalities ◽  
Quantum Correlations ◽  
Quantum Systems ◽  
Causal Models ◽  
Causal Order ◽  
Quantum Processes ◽  
Causal Explanations ◽  
Causal Structures

AbstractCausal reasoning is essential to science, yet quantum theory challenges it. Quantum correlations violating Bell inequalities defy satisfactory causal explanations within the framework of classical causal models. What is more, a theory encompassing quantum systems and gravity is expected to allow causally nonseparable processes featuring operations in indefinite causal order, defying that events be causally ordered at all. The first challenge has been addressed through the recent development of intrinsically quantum causal models, allowing causal explanations of quantum processes – provided they admit a definite causal order, i.e. have an acyclic causal structure. This work addresses causally nonseparable processes and offers a causal perspective on them through extending quantum causal models to cyclic causal structures. Among other applications of the approach, it is shown that all unitarily extendible bipartite processes are causally separable and that for unitary processes, causal nonseparability and cyclicity of their causal structure are equivalent.

Superposition of causal orders for quantum discrimination of quantum processes

2019 ◽  
Vol 17 (07) ◽  
pp. 1950055
Author(s):  
Seid Koudia ◽  
Abdelhakim Gharbi
Keyword(s):  
Quantum Mechanics ◽  
Memory Effects ◽  
Causal Order ◽  
Quantum Processes ◽  
Quantum Process ◽  
Order Case ◽  
Ultimate Bound ◽  
Process Discrimination

We address the superposition of causal orders in the quantum switch as a convenient framework for quantum process discrimination in the presence of noise in qubit systems, using Bayes strategy. We show that, for different kinds of qubit noises, the indefinite causal order between the unitary to be discriminated and noise gives enhancement compared to the definite causal order case without reaching the ultimate bound of discrimination in general. Whereas, for entanglement breaking channels, the enhancement is significant, where the quantum switch allows for the attainability of the ultimate bound for discrimination posed by quantum mechanics. Memory effects escorting the superposition of causal orders are discussed, where we point out that processes describing an indefinite causal order, violate the notion of Markov locality. Accordingly, a suggestion for the simulation of indefinite causal orders in more generic scenarios beyond the quantum switch is given.

scholarly journals QUANTUM MECHANICS, TIME, AND THEOLOGY: INDEFINITE CAUSAL ORDER AND A NEW APPROACH TO SALVATION

Zygon® ◽  
2020 ◽  
Vol 55 (3) ◽  
pp. 663-684
Author(s):  
Emily Qureshi‐Hurst ◽  
Anna Pearson
Keyword(s):  
Quantum Mechanics ◽  
Causal Order ◽  
New Approach

The Comparative Analysis of Coalition Formation and Duration: Distinguishing Between-Country and Within-Country Effect

1989 ◽  
Vol 19 (2) ◽  
pp. 291-302 ◽  
Author(s):  
Bernard Grofman
Keyword(s):  
Coalition Formation ◽  
Causal Structure ◽  
Empirical Support ◽  
System Level ◽  
National Data ◽  
Highly Correlated ◽  
Using Data ◽  
Number Of Parties ◽  
Minimal Winning Coalitions ◽  
Cross National

Dodd is generally credited with providing clear empirical support for the proposition that, in the period after the Second World War, minimal winning coalitions in European party governments will tend to last longer in office than non-minimal winning coalitions. There has been a considerable body of research on this and related questions. Dodd, as well as most other authors treating cabinet coalition formation, has attempted to model features of cabinet formation such as cabinet duration or cabinet type (e.g. minimal winning v. minority government v. oversized coalitions) largely or entirely using data pooled from all cabinets in each of a number of different countries over some considerable time period. One difficulty with this method is that system-level variables (such as number of parties, or the presence of large anti-system parties), which might be able to explain aggregate-level between-county variations in cabinet type or cabinet durability, are not likely to be the same variables that are useful in explaining within-country differences. A second difficulty is that certain system-level characteristics such as effective number of parties or number of cleavage dimensions are highly correlated with both cabinet type and cabinet duration and, as a consequence, these variables are highly correlated with one another when pooled cross-national data are used. Thus, if the analyst is not very careful, results of pooled cross-national data may lead to mistakes about causal structure and a confusion of within-country and between-country effects.

scholarly journals Causation does not explain contextuality

Quantum ◽  
2018 ◽  
Vol 2 ◽  
pp. 63 ◽  
Author(s):  
Sally Shrapnel ◽  
Fabio Costa
Keyword(s):  
Quantum Mechanics ◽  
Causal Structure ◽  
Quantum Correlations ◽  
Global Constraints ◽  
Local Constraints ◽  
The Past ◽  
Interpretations Of Quantum Mechanics ◽  
The World ◽  
Non Local ◽  
Initial States

Realist interpretations of quantum mechanics presuppose the existence of elements of reality that are independent of the actions used to reveal them. Such a view is challenged by several no-go theorems that show quantum correlations cannot be explained by non-contextual ontological models, where physical properties are assumed to exist prior to and independently of the act of measurement. However, all such contextuality proofs assume a traditional notion of causal structure, where causal influence flows from past to future according to ordinary dynamical laws. This leaves open the question of whether the apparent contextuality of quantum mechanics is simply the signature of some exotic causal structure, where the future might affect the past or distant systems might get correlated due to non-local constraints. Here we show that quantum predictions require a deeper form of contextuality: even allowing for arbitrary causal structure, no model can explain quantum correlations from non-contextual ontological properties of the world, be they initial states, dynamical laws, or global constraints.

scholarly journals Formale Mehrkanal-Streutheorie

1960 ◽  
Vol 15 (4) ◽  
pp. 311-319
Author(s):  
Gerald Gbawert ◽  
Joachim Petzold
Keyword(s):  
Quantum Mechanics ◽  
Particle System ◽  
Formal Theory ◽  
Exclusion Principle ◽  
Alternative Formulation ◽  
Matrix Formalism ◽  
Nonrelativistic Quantum ◽  
System A ◽  
S Matrix ◽  
Nonrelativistic Quantum Mechanics

An alternative formulation is presented of the formal theory of multi-channel scattering in nonrelativistic quantum mechanics. We start by defining spaces of state vectors, where two particles either stay together or separate in the limit t →+∞ (or — ∞), when the state vector develops in time by e–i H t (H is the complete Hamiltonian of the n-particle system). A channel is defined as a space of state vectors with the following property: Developing in time by e-i H t they asymptotically describe a state of the n-particle system, where the particles are grouped in fragments. Defining a Hamiltonian Hγ for each channel, in which—compared to H—the interactions acting between particles from different fragments are missing, it is physically plausible that lim eiH e—iHt Ψ exists for vectors Ψ in the channel. Having discussed the limit vectors (asymptotic states), the S-matrix formalism can be introduced as usual. Finally the introduction of the exclusion principle is discussed.

Time

2018 ◽  
Author(s):  
Lawrence Sklar
Keyword(s):  
Quantum Mechanics ◽  
Statistical Mechanics ◽  
Physical Theory ◽  
Temporal Order ◽  
Fundamental Concept ◽  
Causal Order ◽  
Newtonian Dynamics ◽  
The Asymmetry ◽  
Immediate Experience

Time is the single most pervasive component of our experience and the most fundamental concept in our physical theories. For these reasons time has received intensive attention from philosophy. Reflection on our ordinary-tensed language of time has led many to posit a relation of metaphysical importance between time and existence. Closely connected with such intuitions are claims to the effect that time is unlike space, and in deep and important ways. The development of physical theories from Newtonian dynamics through relativistic theories, statistical mechanics, and quantum mechanics has had a profound effect on philosophical views about time. Relativity threatens the notion of a universal, global present, and with it the alleged connections of time to existence. The connection between temporal order and causal order in relativity theories, and between the asymmetry of time and entropic asymmetry in statistical mechanics, suggest various ‘reductive’ accounts of temporal phenomena. Finally, the radical differences between time as it appears in our physical theory and time as it appears in our immediate experience, show important and difficult problems concerning the relation of the time of ‘theory’ to the time of ‘our immediate awareness’.

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