Measurement simulability and incompatibility in quantum theory and other operational theories

TL;DR

This paper explores measurement simulability and incompatibility in quantum and other operational theories, analyzing how measurement devices can be simulated, restricted, and how these properties relate to fundamental principles like no-free-information.

Contribution

It introduces a framework for measurement simulation in operational theories, linking simulability to measurement compatibility and physical restrictions, and discusses implications for quantum and non-classical theories.

Findings

Measurement simulation induces a structured classification of measurement restrictions.

Simulation relates to measurement compatibility and generalizes it.

The no-free-information principle holds in quantum theory but can be violated in other theories.

Abstract

In this thesis, we consider the properties of measurements in quantum theory and other operational theories. After having introduced the framework of operational theories, we consider a communication scheme based on an experimental prepare-and-measure scenario and demonstrate this with different communication tasks. This gives us context for how the different communication tasks can be implemented in different theories, in doing so establishing quantum theory intuitively as an operational theory among other theories. The main property of measurements we focus on in this work is the simulation of measurements, which consists of manipulating the inputs and outputs of the measurement devices. We study how using this process on existing measurement devices can be used to operationally imitate new devices, and what kind of structure the simulation process induces on measurements. We also consider applications of simulability. Firstly, we consider operational restrictions imposed upon measurements. We argue that the restricted set of physical measurements must be closed with respect to the simulation process since the simulation of physical devices must lead to other physically feasible devices. We demonstrate different types of restrictions by classifying them. As a second application we see how the simulation of measurements relates to compatibility of measurements and how it can be viewed as a generalisation of it. This allows us to present an operational principle previously known to quantum theory, the no-free-information principle, according to which any measurement that is compatible with all other measurement must not provide any useful, and therefore free, information about the system. Whilst this principle holds in quantum theory, there are non-classical theories for which it is violated, and so enforcing this principle may be considered a way to exclude some unphysical theories.