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Entropy 2018, 20(9), 687;

Classical and Quantum Causal Interventions

Centre for Engineered Quantum Systems, School of Mathematics and Physics, The University of Queensland, Brisbane 4067, Australia
Author to whom correspondence should be addressed.
Received: 29 June 2018 / Revised: 23 August 2018 / Accepted: 7 September 2018 / Published: 8 September 2018
(This article belongs to the Special Issue Quantum Causal Networks)
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Characterising causal structure is an activity that is ubiquitous across the sciences. Causal models are representational devices that can be used as oracles for future interventions, to predict how values of some variables will change in response to interventions on others. Recent work has generalised concepts from this field to situations involving quantum systems, resulting in a new notion of quantum causal structure. A key concept in both the classical and quantum context is that of an intervention. Interventions are the controlled operations required to identify causal structure and ultimately the feature that endows causal models with empirical meaning. Although interventions are a crucial feature of both the classical and quantum causal modelling frameworks, to date there has been no discussion of their physical basis. In this paper, we consider interventions from a physical perspective and show that, in both the classical and quantum case, they are constrained by the thermodynamics of measurement and feedback in open systems. We demonstrate that the perfect “atomic” or “surgical” interventions characterised by Pearl’s famous do-calculus are physically impossible, and this is the case for both classical and quantum systems. View Full-Text
Keywords: causality; control; quantum thermodynamics; quantum measurement causality; control; quantum thermodynamics; quantum measurement

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Milburn, G.; Shrapnel, S. Classical and Quantum Causal Interventions. Entropy 2018, 20, 687.

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