Entanglement and boundary critical phenomena

We investigate boundary critical phenomena from a quantum information perspective. Bipartite entanglement in the ground state of one-dimensional quantum systems is quantified using the Renyi entropy S_alpha, which includes the von Neumann entropy (alpha=1) and the single-copy entanglement (alpha=infinity) as special cases. We identify the contribution from the boundary entropy to the Renyi entropy, and show that there is an entanglement loss along boundary renormalization group (RG) flows. This property, which is intimately related to the Affleck-Ludwig g-theorem, can be regarded as a consequence of majorization relations between the spectra of the reduced density matrix along the boundary RG flows. We also point out that the bulk contribution to the single-copy entanglement is half of that to the von Neumann entropy, whereas the boundary contribution is the same.Comment: 4 pages, 2 figure

Universal bounds on the performance of information-thermodynamic engine

We investigate fundamental limits on the performance of information processing systems from the perspective of information thermodynamics. We first extend the thermodynamic uncertainty relation (TUR) to a subsystem. Specifically, for a bipartite composite system consisting of a target system and an auxiliary system, we show that the relative fluctuation of an arbitrary current for the target system is lower bounded not only by the entropy production associated with the target system but also by the information flow between the two systems. As a direct consequence of this bipartite TUR, we prove universal trade-off relations between the output power and efficiency of an information-thermodynamic engine in the fast relaxation limit of the auxiliary system. In this limit, we further show that the Gallavotti-Cohen symmetry is satisfied even in the presence of information flow. This symmetry leads to universal relations between the fluctuations of information flow and entropy production in the linear response regime. We illustrate these results with simple examples: coupled quantum dots and coupled linear overdamped Langevin equations. Interestingly, in the latter case, the equality of the bipartite TUR is achieved even far from equilibrium, which is a very different property from the standard TUR. Our results are applicable to a wide range of systems, including biological systems, and thus provide insight into the design principles of biological systems.Comment: 26 pages, 4 figure

Discourse and sociotechnical transformation: the emergence of refinery information systems

This thesis considers the emergence and diffusion of British Petroleum's (BP) Refinery Information Systems (RIS). Insights from the associology of translation are coupled with the Foucauldian concepts of discourse and power /knowledge in order to analyse accounts of the system provided by organisational participants. The analysis suggests that a new form of managerialism, or "new commercial agenda" is being selectively deployed both within BP and within the wider commercial world. This transformed managerialism seeks to maintain control and heighten commercialism through a re- working of hierarchical relations within the organisation. Artefacts and practices of organisational life are revealed as prime vehicles for instantiating this new agenda and BP's Refinery Information Systems are thus seen to be both a condition and a consequence of the changes underway

Semi-quantitative comparative analysis

Comparative analysis (CA) of dynamical systems is an important problem in qualitative reasoning. CA techniques predict differences in the behavior of two systems as a consequence of differences in the initial conditions or structural differences. A disadvantage of these techniques is the imprecision of the possible answers due to their qualitative nature. This report presents SQCA, an implemented technique for the semi-quantitative comparative analysis of dynamical systems. SQCA is both able to deal with incompletely specified models and make precise predictions by exploiting numerical information in the formof interval bounds on variable values and envelope functions around monotonic relations. The technique has a solid mathematical foundation which facilitates proofs of correctness and convergence properties

Glimmers of a pre-geometric perspective

Space-time measurements and gravitational experiments are made by using objects, matter fields or particles and their mutual relationships. As a consequence, any operationally meaningful assertion about space-time is in fact an assertion about the degrees of freedom of the matter (\emph{i.e} non gravitational) fields; those, say for definiteness, of the Standard Model of particle physics. As for any quantum theory, the dynamics of the matter fields can be described in terms of a unitary evolution of a state vector in a Hilbert space. By writing the Hilbert space as a generic tensor product of "subsystems" we analyse the evolution of a state vector on an information theoretical basis and attempt to recover the usual space-time relations from the information exchanges between these subsystems. We consider generic interacting second quantized models with a finite number of fermionic degrees of freedom and characterize on physical grounds the tensor product structure associated with the class of "localized systems" and therefore with "position". We find that in the case of free theories no space-time relation is operationally definable. On the contrary, by applying the same procedure to the simple interacting model of a one-dimensional Heisenberg spin chain we recover the tensor product structure usually associated with "position". Finally, we discuss the possible role of gravity in this framework.Comment: 30 page