Study of 'ratio' automatically assembled structures final report, 15 jun. 1963 - 15 jun. 1964

Structural analysis of RATIO automatically assembled panel sections for application to spaceborne paraboloidal antenn

Topological Protection and Quantum Noiseless Subsystems

Encoding and manipulation of quantum information by means of topological degrees of freedom provides a promising way to achieve natural fault-tolerance that is built-in at the physical level. We show that this topological approach to quantum information processing is a particular instance of the notion of computation in a noiseless quantum subsystem. The latter then provide the most general conceptual framework for stabilizing quantum information and for preserving quantum coherence in topological and geometric systems.Comment: 4 Pages LaTeX. Published versio

Filosofía y medicina en la antigua Grecia: modelos de conocimiento y sus repercusiones

This paper investigates some of the complexities in the relationship between philosophy and medicine in ancient Greece. Some philosophers cite medicine as an analogue to philosophy, for instance in connection with the claim that there can be objective experts to whom mere lay people should defer. Some doctors, however, object to what they represent as the dogmatic, 'a priori', strands of philosophical inquiry and develop an alternative, empiricist, epistemology and methodology. Recollection and experience are invoked in strikingly divergent ways as the debate within and between different philosophical and medical traditions developed.En este trabajo se investigan algunas de las complejidades de la relación entre la filosofía y la medicina en la antigua Grecia. Algunos filósofos citan la medicina como análoga de la filosofía, por ejemplo en conexión con la afirmación de que puede haber expertos objetivos a quienes los meros profanos deben someterse. Algunos médicos, sin embargo, ponen objeciones a lo que representan como líneas dogmáticas, apriorísticas, de la indagación filosófica, y desarrollan una epistemología y una metodología alternativas de carácter empírico. El recuerdo y la experiencia se invocan de formas llamativamente divergentes porque el debate se desarrollaba dentro de y entre diferentes tradiciones filosóficas y médicas

A Discrete Four Stroke Quantum Heat Engine Exploring the Origin of Friction

The optimal power performance of a first principle quantum heat engine model shows friction-like phenomena when the internal fluid Hamiltonian does not commute with the external control field. The model is based on interacting two-level-systems where the external magnetic field serves as a control variable.Comment: 4 pages 3 figure

Spintronics and Quantum Dots for Quantum Computing and Quantum Communication

Control over electron-spin states, such as coherent manipulation, filtering and measurement promises access to new technologies in conventional as well as in quantum computation and quantum communication. We review our proposal of using electron spins in quantum confined structures as qubits and discuss the requirements for implementing a quantum computer. We describe several realizations of one- and two-qubit gates and of the read-in and read-out tasks. We discuss recently proposed schemes for using a single quantum dot as spin-filter and spin-memory device. Considering electronic EPR pairs needed for quantum communication we show that their spin entanglement can be detected in mesoscopic transport measurements using metallic as well as superconducting leads attached to the dots.Comment: Prepared for Fortschritte der Physik special issue, Experimental Proposals for Quantum Computation. 15 pages, 5 figures; typos corrected, references adde

Quantum search without entanglement

Entanglement of quantum variables is usually thought to be a prerequisite for obtaining quantum speed-ups of information processing tasks such as searching databases. This paper presents methods for quantum search that give a speed-up over classical methods, but that do not require entanglement. These methods rely instead on interference to provide a speed-up. Search without entanglement comes at a cost: although they outperform analogous classical devices, the quantum devices that perform the search are not universal quantum computers and require exponentially greater overhead than a quantum computer that operates using entanglement. Quantum search without entanglement is compared to classical search using waves.Comment: 9 pages, TeX, submitted to Physical Review Letter

Analog quantum error correction

Quantum error-correction routines are developed for continuous quantum variables such as position and momentum. The result of such analog quantum error correction is the construction of composite continuous quantum variables that are largely immune to the effects of noise and decoherence.Comment: Ten pages, Te