Secure Coherent-state Quantum Key Distribution Protocols with Efficient Reconciliation

We study the equivalence between a realistic quantum key distribution protocol using coherent states and homodyne detection and a formal entanglement purification protocol. Maximally-entangled qubit pairs that one can extract in the formal protocol correspond to secret key bits in the realistic protocol. More specifically, we define a qubit encoding scheme that allows the formal protocol to produce more than one entangled qubit pair per coherent state, or equivalently for the realistic protocol, more than one secret key bit. The entanglement parameters are estimated using quantum tomography. We analyze the properties of the encoding scheme and investigate its application to the important case of the attenuation channel.Comment: REVTeX, 11 pages, 2 figure

Quasiparticle entanglement: redefinition of the vacuum and reduced density matrix approach

A scattering approach to entanglement in mesoscopic conductors with independent fermionic quasiparticles is discussed. We focus on conductors in the tunneling limit, where a redefinition of the quasiparticle vacuum transforms the wavefunction from a manybody product state of noninteracting particles to a state describing entangled two-particle excitations out of the new vacuum. The approach is illustrated with two examples (i) a normal-superconducting system, where the transformation is made between Bogoliubov-de Gennes quasiparticles and Cooper pairs, and (ii) a normal system, where the transformation is made between electron quasiparticles and electron-hole pairs. This is compared to a scheme where an effective two-particle state is derived from the manybody scattering state by a reduced density matrix approach.Comment: Submitted to New Journal of Physics, Focused Issue on "Solid State Quantum Information". 19 pages, 7 figure

Information Nano-Technologies: Transition from Classical to Quantum

In this presentation are discussed some problems, relevant with application of information technologies in nano-scale systems and devices. Some methods already developed in quantum information technologies may be very useful here. Here are considered two illustrative models: representation of data by quantum bits and transfer of signals in quantum wires.Comment: LaTeX (article class), 10 pages, 3 figures (from 6 eps files

Tracing the Biological Roots of Knowledge

The essay is a critical review of three possible approaches in the theory of knowledge while tracing the biological roots of knowledge: empiricist, rationalist and developmentalist approaches. Piaget's genetic epistemology, a developmentalist approach, is one of the first comprehensive treatments on the question of tracing biological roots of knowledge. This developmental approach is currently opposed, without questioning the biological roots of knowledge, by the more popular rationalist approach, championed by Chomsky. Developmental approaches are generally coherent with cybernetic models, of which the theory of autopoiesis proposed by Maturana and Varela made a significant theoretical move in proposing an intimate connection between metabolism and knowledge. Modular architecture is currently considered more or less an undisputable model for both biology as well as cognitive science. By suggesting that modulation of modules is possible by motor coordination, a proposal is made to account for higher forms of conscious cognition within the four distinguishable layers of the human mind. Towards the end, the problem of life and cognition is discussed in the context of the evolution of complex cognitive systems, suggesting the unique access of phylogeny during the ontogeny of human beings as a very special case, and how the problem cannot be dealt with independent of the evolution of coding systems in nature

Machine vision and the OMV

The orbital Maneuvering Vehicle (OMV) is intended to close with orbiting targets for relocation or servicing. It will be controlled via video signals and thruster activation based upon Earth or space station directives. A human operator is squarely in the middle of the control loop for close work. Without directly addressing future, more autonomous versions of a remote servicer, several techniques that will doubtless be important in a future increase of autonomy also have some direct application to the current situation, particularly in the area of image enhancement and predictive analysis. Several techniques are presentet, and some few have been implemented, which support a machine vision capability proposed to be adequate for detection, recognition, and tracking. Once feasibly implemented, they must then be further modified to operate together in real time. This may be achieved by two courses, the use of an array processor and some initial steps toward data reduction. The methodology or adapting to a vector architecture is discussed in preliminary form, and a highly tentative rationale for data reduction at the front end is also discussed. As a by-product, a working implementation of the most advanced graphic display technique, ray-casting, is described