Abstract In this letter, we will investigate causality in string field theory using pp -wave light-cone gauge string field theory. We will generalise the Ramsey scheme to string field theory, and use it to analyze string field theoretical processes. An explicit characteristic function for interactive string field theory will be built using this string field theoretical Ramsey scheme. The average of the difference between the initial and final values of any operator described in string field theory will be obtained using this characteristic function. We will use the quantum information theoretical technique based on quantum Fisher information to extract information about such string field theoretical processes.
Abstract In this letter, we will investigate causality in string field theory using pp -wave light-cone gauge string field theory. We will generalise the Ramsey scheme to string field theory, and use it to analyze string field theoretical processes. An explicit characteristic function for interactive string field theory will be built using this string field theoretical Ramsey scheme. The average of the difference between the initial and final values of any operator described in string field theory will be obtained using this characteristic function. We will use the quantum information theoretical technique based on quantum Fisher information to extract information about such string field theoretical processes.
Abstract In this paper, we analyze the evolution of physical quantities due to the interaction of strings with background fields. We will obtain the characteristic function for such a string theoretical process. This will be done by generalizing the Ramsey scheme to world-sheet, and using it to obtain the information about the evolution of quantity in a string theoretical process, without making two-point measurements. We will also use the characteristic function to obtain the average of the difference between the initial and final values of such a quantity. Finally, using the characteristic function, we calculate the Fisher information for the difference of such a quantity.
This paper investigates the potential interplay between string theory and quantum information theory, exploring how the inherent quantum properties of strings might influence the fundamental laws governing quantum information. We propose a novel model, the "String Quantum Information" framework, which connects string's quantum behavior directly to the principles of quantum information. The core of this research lies in analyzing string quantum properties to uncover underlying patterns within quantum information. This investigation aims to deepen our understanding of the relationship between these two fundamental branches of physics, potentially leading to new insights into the nature of information and its manipulation. Core Claim The core assertion of this paper is that the quantum nature of strings, particularly their inherent non-linearity, possesses a profound influence on the structure and evolution of quantum information. Specifically, we hypothesize that the subtle yet critical quantum properties of strings – such as entanglement and superposition – can act as a fundamental driver in the formation of quantum information, thereby shaping the laws governing quantum computation. The study will analyze the interplay between these quantum properties and the inherent limitations and potential of quantum information to explore potential connections and divergences. Core Mechanism We propose a "String Quantum Information" model, a conceptual framework that integrates string theory with quantum information theory. This model posits that string's quantum properties, especially its inherent non-linearity, are not merely a background phenomenon but an active contributor to the dynamics of quantum information. Instead of viewing quantum information as a purely deterministic process, we suggest that the very fabric of strings – through their quantum characteristics – can introduce a non-linearity that is essential for the creation and manipulation of information. The model will involve developing a mathematical framework that describes how string dynamics, specifically its quantum properties, can translate into patterns within the structure of quantum information. The model will be built to test predictions and to provide a framework for understanding the dynamics of quantum information that is not fully captured by traditional models. Why It Is New Traditional approaches to quantum information often treat quantum computation as a distinct field, largely separate from string theory. While string theory offers a potential pathway to quantum gravity, it lacks a direct, intuitive connection to the fundamental laws governing information. This paper tackles this gap by proposing a dynamic interplay between string theory and quantum information, aiming to reveal a deeper, more holistic understanding of the relationship between these two disciplines. The model we propose – the "String Quantum Information" framework – is novel because it explicitly links the fundamental quantum properties of strings to the very essence of quantum information – specifically, the inherent non-linearity. Existing research often focuses on specific aspects of quantum information without considering the potential influence of string theory's quantum properties. This paper's aim is to provide a conceptual bridge between these two fields, moving beyond a purely theoretical perspective to explore potential practical implications and to develop a more robust mathematical model. Discussion of the Model: A Deep Dive into String Quantum Properties The "String Quantum Information" model centers around a carefully selected set of string properties that we believe are critical to the formation of quantum information. These properties are not simply descriptive; they are inherently linked to the behavior of quantum information. We begin with the concept of entanglement, and how entanglement can influence the evolution of quantum information. Entanglement creates correlations between different parts of a quantum system, and this is a key aspect of quantum information. We hypothesize that the inherent entanglement of strings, through their quantum properties, could be a foundational element in the creation of quantum information. Specifically, we will investigate the role of quantum fluctuations within the string landscape. These fluctuations, driven by the underlying quantum nature of the strings, are expected to subtly alter the quantum state of the system, leading to the emergence of patterns that are essential for quantum information processing. We hypothesize that these fluctuations, driven by the string's quantum properties, can lead to non-linearities which are fundamental to the creation of complex quantum information. The model will incorporate a stochastic element, where the string's quantum properties are not precisely defined but rather subject to probabilistic changes, further increasing the complexity and non-linearity of the system.
Entanglement entropy for spatial subregions is difficult to define in string theory because of the extended nature of strings. Here we propose a definition for bosonic open strings using the framework of string field theory. The key difference (compared to ordinary quantum field theory) is that the subregion is chosen inside a Cauchy surface in the ``space of open string configurations.'' We first present a simple calculation of this entanglement entropy in free light-cone string field theory, ignoring subtleties related to the factorization of the Hilbert space. We reproduce the answer expected from an effective field theory point of view, namely a sum over the one-loop entanglement entropies corresponding to all the particle-excitations of the string, and further show that the full string theory regulates ultraviolet divergences in the entanglement entropy. We then revisit the question of factorization of the Hilbert space by analyzing the covariant phase-space associated with a subregion in Witten's covariant string field theory. We show that the pure gauge (i.e., BRST exact) modes in the string field become dynamical at the entanglement cut. Thus, a proper definition of the entropy must involve an extended Hilbert space, with new stringy edge modes localized at the entanglement cut.
Abstract Causality is pivotal to our understanding of the world, presenting itself in different forms: information-theoretic and relativistic, the former linked to the flow of information, and the latter to the structure of space-time. Leveraging a framework introduced in PRA, 106, 032204 (2022), which formally connects these two notions in general physical theories, we study their interplay. The framework defines information-theoretic causality through a causal modelling approach, which enables the inference of causal connections through agents’ interventions and correlations. First, we improve the characterization of information-theoretic signalling as defined through so-called affects relations. Specifically, we provide conditions for identifying redundancies in different parts of such a relation, introducing techniques for causal inference in unfaithful causal models (where the observable data does not ‘faithfully’ reflect the causal dependences). In particular, this demonstrates the possibility of causal inference using the absence of signalling between certain nodes. Second, we define an order-theoretic property called conicality, showing that it is satisfied for light cones in Minkowski space-times with d > 1 spatial dimensions but violated for d = 1. Finally, we study the embedding of information-theoretic causal models in space-time without violating relativistic principles such as no superluminal signalling (NSS). In general, we observe that constraints imposed by NSS in a space-time and those imposed by purely information-theoretic causal inference behave differently. We then prove a correspondence between conical space-times and faithful causal models: in both cases, there emerges a parallel between these two types of constraints. This indicates a connection between informational and geometric notions of causality, and offers new insights and tools for studying the relations between the principles of NSS and no causal loops in different space-time geometries and theories of information processing.
In this dissertation, I will argue that quantum field theory can be interpreted as a description of causal interactions. I will first discuss previous theories of physical causation, and come to the conclusion that they are inapplicable in quantum field theory. As a consequence, I will start to develop a new theory of causation by first analysing the concept ‘causation’ into the most basic and widely shared intuitions, in order to find out later whether these intuitions can be reduced to physics. I will then have a closer look on the intuition that causation is a directed relation, which is commonly regarded as incompatible with the symmetries of physics. I will present a new argument to the effect that causation and quantum field theory are compatible with respect to the directionality of causation. After that, I will analyse the theoretical description of interactions in quantum field theory, and in particular group structure, locality and local conservation laws will crystallise as the central concepts that a causal interpretation might be based on. Subsequently, I will discuss and present replies to what I believe are the most relevant objections to a causal interpretation of physics, namely, Haag’s theorem, the measurement problem and entanglement. In the final chapter of this dissertation, I will conjoin the results of the previous chapters to a new theory of causation for quantum field theory. The main result will be that a causal process is a quantum field theoretical interaction, i.e., the exchange of energy from an initial to a final state via a force.
We first derive the Jarzynski relation [1] between the average exponential of the thermodynamical work and the exponential of the difference between the initial and final free energy. We then comment on the information-theoretic underpinning of Jarzynski’s reasoning which helps explain why the Jarzynski relation holds identically both quantumly and classically [2]. We then present a scheme to verify the quantum non-equilibrium fluctuation relations as encapsulated by Jarzynski. We show that the characteristic function of the work distribution of a quantum system (which is basically equal to the Wick rotated average exponential of the thermodynamical work) can be extracted from Ramsey interferometry of a single probe qubit (which need not itself be pure, though it must not be fully depolarized) [3,4].We first derive the Jarzynski relation [1] between the average exponential of the thermodynamical work and the exponential of the difference between the initial and final free energy. We then comment on the information-theoretic underpinning of Jarzynski’s reasoning which helps explain why the Jarzynski relation holds identically both quantumly and classically [2]. We then present a scheme to verify the quantum non-equilibrium fluctuation relations as encapsulated by Jarzynski. We show that the characteristic function of the work distribution of a quantum system (which is basically equal to the Wick rotated average exponential of the thermodynamical work) can be extracted from Ramsey interferometry of a single probe qubit (which need not itself be pure, though it must not be fully depolarized) [3,4]. An interesting fact is that while the quantum version of the Jarzynski equality remains satisfied even in the presence of quantum correlations, the individual thermodynamical work moments in the expansion of the free energy are, in fact, sensitive to the genuine quantum correlations [5]. Whether this is a fortuitous coincidence remains to be seen, but it certainly goes towards explaining why the laws of thermodynamics happen to be so robust as to be independent of the underlying micro-physics.We intend to elucidate the subtle connection between Jarzynski’s relation and the “quantum arrow of time”. Finally we comment on the fact that our scheme for measuring the quantum work characteristic function belongs to the computational class known as DCQ1 [6], namely all computations that can be performed with only one pure qubit (and N maximally mixed ones).