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Causal and causally separable processes
The idea that events are equipped with a partial causal order is central to our understanding of physics in the tested regimes: given two pointlike events A and B, either A is in the causal past ofExpand
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Witnessing causal nonseparability
TLDR
We show that the quantum switch, a recently demonstrated resource for quantum computation, can be conveniently represented as a causally non-separable process matrix. Expand
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A quantum causal discovery algorithm
TLDR
We present a causal discovery algorithm for quantum systems that can discover an initially unknown causal structure in a quantum network. Expand
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Indefinite Causal Order in a Quantum Switch.
Quantum mechanics allows events to happen with no definite causal order: this can be verified by measuring a causal witness, in the same way that an entanglement witness verifies entanglement. Here,Expand
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Witnessing Causal Nonseparability: Theory and Experiment
TLDR
We develop a technique to witness a process that is not causally separable, in that it cannot be written as a fixed-order quantum circuit or a mixture of those. Expand
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Experimental test of nonlocal causality
Causation at a distance does not explain quantum correlations. Explaining observations in terms of causes and effects is central to empirical science. However, correlations between entangled quantumExpand
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Multipartite causal correlations: Polytopes and inequalities
We consider the most general correlations that can be obtained by a group of parties whose causal relations are well defined, although possibly probabilistic and dependent on past parties'Expand
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Witnessing quantum memory in non-Markovian processes
We present a method to detect a quantum memory in a non-Markovian process. We call a process Markovian when the environment does not provide a memory that retains correlations across consecutiveExpand
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Violation of a causal inequality in a spacetime with definite causal order
Processes with an indefinite causal structure may violate a causal inequality, which quantifies quantum correlations that arise from a lack of causal order. In this paper, we show that when theExpand
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Spatial modes for testing indefinite causal order
TLDR
We use polarisation as a control for the order of the operations that act on the spatial mode of a photon. Expand