Unlimited non-causal correlations and their relation to non-locality
1Institute for Quantum Optics and Quantum Information (IQOQI-Vienna), Austrian Academy of Sciences, 1090 Vienna, Austria
2Faculty of Physics, University of Vienna, 1090 Vienna, Austria
3Facoltà indipendente di Gandria, 6978 Gandria, Switzerland
4Department of Computer Science, University of Maryland, College Park, Maryland 20742, USA
5School of Mathematics and Computer Science, Institute of Business Administration, Karachi, Pakistan
Published: | 2022-03-29, volume 6, page 673 |
Eprint: | arXiv:2104.06234v3 |
Doi: | https://doi.org/10.22331/q-2022-03-29-673 |
Citation: | Quantum 6, 673 (2022). |
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Abstract
Non-causal correlations certify the lack of a definite causal order among localized space-time regions. In stark contrast to scenarios where a single region influences its own causal past, some processes that distribute non-causal correlations satisfy a series of natural desiderata: logical consistency, linear and reversible dynamics, and computational tameness. Here, we present such processes among arbitrary many regions where each region influences every other but itself, and show that the above desiderata are altogether $\textit{insufficient to limit the amount of "acausality"}$ of non-causal correlations. This leaves open the identification of a principle that forbids non-causal correlations. Our results exhibit $\textit{qualitative and quantitative parallels}$ with the non-local correlations due to Ardehali and Svetlichny.
![](https://quantum-journal.org/wp-content/uploads/2022/03/featuredimage.png)
Featured image: This figure shows various correlation sets for $n$ parties. Bi-causal inequalities bound the set of correlations that are obtained by partitioning the $n$ parties in two sets, and where only one set can influence the other. Correlations that lie outside this set are genuinely multi-party non-causal. The processes reported in this work establish the non-causal correlations $G_n$. The degree of violation of the respective bi-causal inequality increases with $n$. More so, the processes do not require any quantum-theoretic features, and are therefore obtained with classical processes.
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[1] Ravi Kunjwal and Ämin Baumeler, "Trading Causal Order for Locality", Physical Review Letters 131 12, 120201 (2023).
[2] Alessandro Capurso, "The Universe as a Telecommunication Network", Journal of Physics: Conference Series 2533 1, 012045 (2023).
[3] Alessandro Capurso, "The Potential of a Thick Present through Undefined Causality and Non-Locality", Entropy 24 3, 410 (2022).
[4] Eleftherios-Ermis Tselentis and Ämin Baumeler, "Admissible Causal Structures and Correlations", PRX Quantum 4 4, 040307 (2023).
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