Quantum State Readout, Collapses, Probes and Signals

TL;DR

This paper explores hypothetical devices that could read quantum states locally without superluminal signaling, potentially revealing new physics and implications for quantum theory and gravity.

Contribution

It introduces a model for local quantum state readout devices that extend quantum theory and discusses their scientific and practical implications.

Findings

Potential for signaling through opaque media

Probing distant quantum systems without reflected signals

Detecting collapse dynamics without direct observation

Abstract

Theories involving localized collapse allow the possibility that classical information could be obtained about quantum states without using POVMS and without allowing superluminal signalling. We can model this by extending quantum theory to include hypothetical devices that read out information about the local quantum state at a given point, defined by considering only collapses in its past light cone. Like Popescu-Rohrlich boxes, these hypothetical devices would have practical and scientific implications if realisable. These include signalling through opaque media, probing the physics of distant or opaque systems without needing a reflected signal and giving detailed information about collapse dynamics without requiring direct observation of the collapsing system. These potential applications motivate systematic searches for possible signatures of these nonstandard extensions of quantum theory, and in particular for relevant gravitational effects, such as the validity of semi-classical gravity on small scales.