Perfect discrimination of no-signalling channels via quantum superposition of causal structures

By Giulio Chiribella. 2011

253 citations recorded by the source corpus.

A no-signalling channel transforming quantum systems in Alice's and Bob's local laboratories is compatible with two different causal structures: ($A⪯B$) Alice's output causally precedes Bob's input and ($B⪯A$) Bob's output causally precedes Alice's input. Here I prove that two no-signalling channels that are not perfectly distinguishable in any ordinary quantum circuit can become perfectly distinguishable through the quantum superposition of circuits with different causal structures.

Subfields: Artificial Intelligence, Atomic and Molecular Physics, and Optics

View Paper: https://www.semanticscholar.org/paper/5e81092f9392127727f88f40052a6d0930d8dfd7

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In Atomic and Molecular Physics, and Optics

Citations in the corpus

Experimental superposition of orders of quantum gates (2014, methodology): “In the standard circuit model this cannot be done with a single use of each gate [3]; this limitation is evident in all previous experimental investigations of commutation relations, which all used one gate at least twice [12, 13].”
The simplest causal inequalities and their violation (2015, background): “A related open question is whether the ability to violate causal inequalities can—in analogy with Bell nonlocality [17]—be exploited as a resource, just like causally non-separable process matrices provide advantages for information-theoretical [18] and computational [19] tasks.”
Quantum common causes and quantum causal models (2016, background): “Finally, it would be interesting to extend the formalism to explore the possibility that certain quantum scenarios are best understood as involving a quantum coherent combination of different causal structures [46,48,83,84].”
Causal and causally separable processes (2015, background): “[6] that by exploiting such a coherent strategy, Charlie can perfectly distinguish between a pair of unitaries UA and UB that commute or anticommute by using each of the unitaries only once, which is impossible if the order of the unitaries is conditioned on a classical bit.”
Indefinite causal order enables perfect quantum communication with zero capacity channels (2018, background): “In recent years, the applications of the quantum SWITCH and other causally non-separable processes have attracted increasing interest, leading to the discovery of quantum advantages in various tasks, such as testing properties of quantum channels [23, 24], winning non-causal games [20], reducing qua”