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Quantum causal loop

Nature Communications .. DOI: 10.1038 / s41467-020-20456-x “width =” 251 “height =” 430 “/>

For any state ρ and any CPTP map EE, this defines the process operators for A and B. credit: Nature Communications.. DOI: 10.1038 / s41467-020-20456-x

It is usually assumed that a causal effect travels in only one direction, from cause to effect, and never returns from effect to cause. Ringing the bell does not press the button that triggered the bell. Researchers at Oxford University and the Free University of Brussels have now developed a theory of causal relationships in quantum theory. According to this, causality can form a cycle. This theory provides a new understanding of exotic processes in which events do not have a clear causal relationship.The study is published at Nature Communications..


One way quantum theory goes against classical intuition is to challenge the idea of ​​causality. Entanglement can be used to generate correlations between distant experiments that are known to circumvent satisfactory causal explanations within the framework of classical causal models. Furthermore, the unification of quantum theory and gravity is expected to enable situations where the causal structure of spacetime is affected by quantum uncertainty, suggesting that events do not need to be causally ordered at all. I am.

Recently, a team of researchers from Oxford and Brussels have developed a theory of causality in quantum theory. In this theory, the concept of causality is essentially defined in quantum terms, rather than being related to the measurements of the classical scales that emerge. This provided an understanding of the causal relationships of the correlations generated by the intertwined states. Now, they generalize the theory, allowing causal effects to progress cyclically and providing a causal understanding of processes with events in an indefinite causal order.

“The important idea behind our proposal is that the causality of quantum theory corresponds to the effects of so-called unitary transformations. These are the types of transformations that explain the evolution of isolated quantum systems. Is very similar to the classical approach to causal models, which presupposes the underlying determinism and brings causality to the functional dependencies between variables, “says Jonathan of Oxford University. Barrett says. The main idea of ​​new research is to apply the same principles to processes where the order of operations is dynamic or even indefinite. Most of these processes can be understood as resulting from unitary transformations. Expand in the normal order.

“Previously, processes with uncertain causal order were usually considered simply incompatible with causal explanations. Our work is in their main class, the single. It can be understood that it arises from the process of, and the physical realization in nature can be regarded as having a clear causal structure, although it is actually accompanied by a cycle. ” Says Robin Lorenz, the corresponding author of. “The idea of ​​a periodic causal structure may seem counter-intuitive, but the quantum process framework in which it is formulated is logical, such as the possibility of going back in time and killing a young self. We guarantee that there is no paradox, “explains Ognyan Oreshkov. Free University of Brussels.

“Although it looks exotic, some of these scenarios are actually known to have experimental realizations in which the variable of interest is delocalized in time.”

Does this mean that space-time does not have the normally assumed aperiodic causal structure? To be precise, in the above experiment, the periodically causal events are space-time and not local. However, researchers believe that the causal structure of space-time itself may circulate in this quantum way at the intersection of quantum theory and general relativity. Here we expect a process similar to what is feasible in the lab, but the events are local to each. Space-time reference frame.


Can quantum mechanics change the causal relationships between events?


For more information:
Circular quantum causal model, Nature Communications.. DOI: 10.1038 / s41467-020-20456-x, www.nature.com / articles / s41467-020-20456-x

Provided by Free University of Brussels

Quote: Quantum Causal Loop (2021, February 9th) was taken from https://phys.org/news/2021-02-quantum-causal-loops.html on February 9th, 2021.

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Quantum causal loop

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