Abstract
It has been more than 20 years since Deutsch and Hayden proved the locality of quantum theory, using the Heisenberg picture of quantum computational networks. Of course, locality holds even in the face of entanglement and Bell’s theorem. Today, most researchers in quantum foundations are still convinced not only that a local description of quantum systems has not yet been provided, but that it cannot exist. The main goal of this paper is to address this misconception by re-explaining the descriptor formalism in a hopefully accessible and self-contained way. It is a step-by-step guide to how and why descriptors work. Finally, superdense coding is revisited in the light of descriptors.
Highlights
It is still a widespread belief that a complete description of a composite entangled quantum system cannot be obtained by descriptions of the parts, if those are expressed independently of what happens to other parts
In the Heisenberg picture, a quantum system shall no longer be described by its state vector, but rather by an object that encodes the information about all the evolved observables of the system
The formalism of descriptors is re-explained in this paper in what I hope is a more complete exposition
Summary
It is still a widespread belief that a complete description of a composite entangled quantum system cannot be obtained by descriptions of the parts, if those are expressed independently of what happens to other parts This apparently holistic feature of entangled quantum states entails violation of Bell inequalities [1,2] and quantum teleportation [3], which are repeatedly invoked to sanctify the “non-local” character of quantum theory. Even entangled systems admit a separable description When such a bold foundational result collects a mere 190 citations in more than 20 years, it is evidence that a large portion of the community of quantum foundations is unaware of the idea or, worse, does not understand it. A background in physics is optional; only introductory knowledge in quantum information theory is required
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