Abstract Since the early 90s, philosophers and physicists have been asking the question, “What is quantum information?” In this paper, I will present Shannon and quantum information theories and a minimal interpretation of them which has come to be known as the deflationary view of information. I will present several criticisms that have been leveled at the deflationary view of quantum information and offer responses. This will provide the reader an up‐to‐date view of the debate over the nature of quantum information.
Abstract Since the early 90s, philosophers and physicists have been asking the question, “What is quantum information?” In this paper, I will present Shannon and quantum information theories and a minimal interpretation of them which has come to be known as the deflationary view of information. I will present several criticisms that have been leveled at the deflationary view of quantum information and offer responses. This will provide the reader an up‐to‐date view of the debate over the nature of quantum information.
Introduction Many philosophers and physicists have expressed great hope that quantum information theory will help us understand the nature of the quantum world. The general problem is that there is no widespread agreement on what quantum information is. Hence, such pronouncements regarding quantum information theory as the savior of the philosophy of physics are hard to evaluate. Much work has been done producing and evaluating concepts of information. In I have defended and articulated the Schumacher concept of quantum information. Roughly speaking, quantum information is construed as the statistical behavior associated with the measurement of a quantum system. Hence it is a coarse-grained operational description of quantum systems, with no recourse to the fundamental ontological features of quantum systems responsible for such behavior. From this perspective, construing quantum mechanics as a theory of quantum information departs from the traditional interpretive endeavors of philosophers and physicists. The question is whether there is any motivation for taking such a view. The theorem of Clifton, Bub, and Halvorson (CBH) provides just such a motivation. The theorem guarantees that, if a theory T satisfies certain conditions, there will exist an empirically equivalent C *-algebraic theory that has a concrete representation in Hilbert space, which it is notoriously difficult to interpret as a constructive or mechanical theory. In such a case, any underlying ontologies philosophers develop that are compatible with T will be undermined by the C*-algebraic equivalent. Bub suggests in light of this in-principle uncertainty regarding ontology that we re-conceive of quantum mechanics as a theory about quantum information.
Information is on everyone's lips.It seems that nowadays there is no philosophical or scientific inquiry that cannot benefit from a reformulation in terms of information theory (IT).Quantum theory (QT) is no exception.Indeed, one of the liveliest debates in the foundations of QT concerns the role that information may play in the solution of the well-known problems in the foundations of QT.For instance, one of the hottest discussions concerns quantum non-locality.On the one hand, IT folks stress how, rather than approaching non-local entanglement as an 'embarrassment', IT invites us to see it as a resource for new information-processing protocols.On the other hand, it is unclear how this invitation can contribute to the solution of the problem of accounting for the apparent nonlocality involved in quantum correlations.Christopher G. Timpson's beautiful book is a welcome contribution to this dialectic.It provides an admirable mix of conceptual and technical analysis of the notion of information and critically analyses the most prominent proposals on the table in the debate over the role of IT in the foundations of QT.Although the focus of Timpson's book is quantum information theory (QIT) and the foundations of QT, a considerable component of its basic precepts will be found extremely useful in any branch (be it more philosophical or more scientific) of applied IT.It is because of this additional value that in this review, sometimes to detriment of exhaustiveness, I prefer to concentrate on providing some samples of Timpson's main argumentative line.This should give a better idea of how this volume can represent valuable reading for both specialists in QIT and non-specialists.First things first.In chapter 2, Timpson provides a sharp analysis of the concepts of information.The plural is due to the necessary distinction between information in the everyday sense and information in the technical sense (informationt).Both are abstract mass nouns, but while the former refers to a semantic and epistemic notion, informationt is a physically defined quantity, measured classically by Shannon information.Informationt is usually described as an undefined notion.Contrary to this claim, at the roots of Timpson's analysis is a neat definition: 'Informationt is what is produced by an informationt source that is required to be reproducible at the destination if the transmission is to be counted a success' (22).Although avowedly deflationary, this definition provides a fertile background to dissipate much of the fog around the nature of informationt and its behaviour.It actually turns out that the majority of the results of this book pivots on this very simple definition.Here is a straightforward example.According to the definition above, a successful transmission requires that the message be reproducible at destination.However, what it is said to be repeatable is not the token of a message, but the type.When we talk about something that is transmitted in communication protocols (the so-called pieces of information) we refer to types, i.e. abstracta, rather than to concrete objects.The operation of conceptual cleansing continues when we pass from classical to quantum informationt (chapter 3).An especially noteworthy result is the rejection of the common view that quantum informationt is different in nature from classical informationt.Timpson's methodology allows instead to account for it as an extension of Shannon informationt.In fact, with the template of classical informationt at hand, Timpson reconstructs the notions of quantum informationt source, measure of quantum informationt and piece of quantum informationt, the latter being a sequence of Hilbert space states.
Over the past decade, quantum information theory has developed into a vigorous field of research despite the fact that quantum information, as a precise concept, is undefined. Indeed, the very idea of viewing quantum states as carriers of some kind of information (albeit unknowable in classical terms) leads naturally to interesting questions that might otherwise never have been asked, and corresponding new insights. We discuss some illustrative examples, including a strengthening of the well-known no-cloning theorem leading to a property of permanence for quantum information, and considerations arising from information compression that reflect on fundamental issues.
The approach to thinking about information developed in the previous chapter is turned towards the quantum theory. First, some of the characteristic ideas and applications of quantum information theory are presented, then the nature of quantum information itself is discussed. With the correct conception of Shannon information to hand, the dimension of generalisation which the quantum concept occupies is made clear. Quantum information is simply what is produced by a quantum information source. As in the classical case, a piece of information will be an abstract type (a sequence of quantum states), rather than a concrete thing or physical substance. This conception is defended from a number of potential objections which might be raised. With a clear grasp obtained of the relation between quantum information and the world, it proves short work to dissect the slogan `Information is Physical’ and dispatch the prospect of informational immaterialism.
By questioning the validity of some of our basic concepts, such as space, object, and causality, quantum physics contributes quite decisively to the dramatic changes now taking place in our world picture.This book is addressed not only to physicists at an early stage in their careers (the first or second year graduate student) but also to philosophers, as well as to all the senior physicists interested in the interpretation problem. Beginning with a chapter that could be described as ?philosophy for physicists,? it presents an in-depth analysis of present-day quantum mechanical concepts, an analysis of physicists and philosophers alike. Specifically, it first offers an extensive critical analysis of such topics as the Einstein, Podolsky, Rosen reality criterion, nonseparatability, the quantum measurement riddle, decoherence theory, consistent histories approaches and ontologically interpretable theories. All this then naturally leads to philosophical questions concerning, in particular, intersubjective agreement and the limit of realism. And a thorough examination of this whole material finally leads to the view that distinguishing between empirical reality and a veiled man-independent reality yields an acceptable answer to the perplexing question of how to interpret quantum physics. Veiled Reality offers nonspecialists, including students in physics, philosophy and the history of science, an accessible perspective on basic problems in the foundations of physics.