Classical Statistics Inherent in a Quantum Density Matrix

A density matrix formulation of classical bipartite correlations is constructed. This leads to an understanding of the appearance of classical statistical correlations intertwined with the quantum correlations as well as a physical underpinning of these correlations. As a byproduct of this analysis, a physical basis of the classical statistical correlations leading to additive entropy in a bipartite system discussed recently by Tsallis et al emerges as inherent classical spin fluctuations. It is found that in this example, the quantum correlations shrink the region of additivity in phase space.Comment: 10 pages, 3 figure

On the Possibility of Quasi Small-World Nanomaterials

The possibility of materials that are governed by a fixed point related to small world networks is discussed. In particular, large-scale Monte Carlo simulations are performed on Ising ferromagnetic models on two different small-world networks generated from a one-dimensional spin chain. One has the small-world bond strengths independent of the length, and exhibits a finite-temperature phase transition. The other has small-world bonds built from atoms, and although there is no finite-temperature phase transition the system shows a slow power-law change of the effective critical temperature of a finite system as a function of the system size. An outline of a possible synthesis route for quasi small-world nanomaterials is presented.Comment: 13 pages, 9 figures, submitted to Brazilian Journal of Physics, conference proceedings for III Brazilian Meeting on Simulational Physics (2003

Entanglement and optimal strings of qubits for memory channels

We investigate the problem of enhancement of mutual information by encoding classical data into entangled input states of arbitrary length and show that while there is a threshold memory or correlation parameter beyond which entangled states outperform the separable states, resulting in a higher mutual information, this memory threshold increases toward unity as the length of the string increases. These observations imply that encoding classical data into entangled states may not enhance the classical capacity of quantum channels.Comment: 14 pages, 8 figures, latex, accepted for publication in Physical Review

Quantum Entanglement Capacity with Classical Feedback

For any quantum discrete memoryless channel, we define a quantity called quantum entanglement capacity with classical feedback ($E_B$), and we show that this quantity lies between two other well-studied quantities. These two quantities - namely the quantum capacity assisted by two-way classical communication ($Q_2$) and the quantum capacity with classical feedback ($Q_B$) - are widely conjectured to be different: there exists quantum discrete memoryless channel for which $Q_2>Q_B$. We then present a general scheme to convert any quantum error-correcting codes into adaptive protocols for this newly-defined quantity of the quantum depolarizing channel, and illustrate with Cat (repetition) code and Shor code. We contrast the present notion with entanglement purification protocols by showing that whilst the Leung-Shor protocol can be applied directly, recurrence methods need to be supplemented with other techniques but at the same time offer a way to improve the aforementioned Cat code. For the quantum depolarizing channel, we prove a formula that gives lower bounds on the quantum capacity with classical feedback from any $E_B$ protocols. We then apply this formula to the $E_B$ protocols that we discuss to obtain new lower bounds on the quantum capacity with classical feedback of the quantum depolarizing channel

The double life of electrons in magnetic iron pnictides, as revealed by NMR

We present a phenomenological, two-fluid approach to understanding the magnetic excitations in Fe pnictides, in which a paramagnetic fluid with gapless, incoherent particle-hole excitations coexists with an antiferromagnetic fluid with gapped, coherent spin wave excitations. We show that this two-fluid phenomenology provides an excellent quantitative description of NMR data for magnetic "122" pnictides, and argue that it finds a natural justification in LSDA and spin density wave calculations. We further use this phenomenology to estimate the maximum renormalisation of the ordered moment that can follow from low-energy spin fluctuations in Fe pnictides. We find that this is too small to account for the discrepancy between ab intio calculations and neutron scattering measurements.Comment: Accepted for publication in Europhys. Lett. 6 pages, 4 figure

Standardised library instruction assessment: an institution-specific approach

Introduction We explore the use of a psychometric model for locally-relevant, information literacy assessment, using an online tool for standardised assessment of student learning during discipline-based library instruction sessions. Method A quantitative approach to data collection and analysis was used, employing standardised multiple-choice survey questions followed by individual, cognitive interviews with undergraduate students. The assessment tool was administered to five general education psychology classes during library instruction sessions. AnalysisDescriptive statistics were generated by the assessment tool. Results. The assessment tool proved a feasible means of measuring student learning. While student scores improved on every survey question, there was uneven improvement from pre-test to post-test for different questions. Conclusion Student scores showed more improvement for some learning outcomes over others, thus, spending time on fewer concepts during instruction sessions would enable more reliable evaluation of student learning. We recommend using digital learning objects that address basic research skills to enhance library instruction programmes. Future studies will explore different applications of the assessment tool, provide more detailed statistical analysis of the data and shed additional light on the significance of overall scores

The Adoption and Management of Soil Conservation Practices in Haiti: The Case of Rock Walls

Farmers are usually reluctant to adopt measures to reduce the toll of soil erosion; and even when soil conservation structures are adopted, farmers fail to manage them. This study investigates factors that influence adoption and management of soil conservation structures in Fort-Jacques, Haiti. The results show that personal characteristics of farmers, institutional factors, such as local group membership, training in soil conservation, per capita income and size of farm influence soil conservation adoption in Forte-Jacques. Age, education, per capita household income, participation in local groups, the interaction of per capita household income and farmers’ age influence rock wall management.Resource /Energy Economics and Policy,