Quantum Limits of Measurements Induced by Multiplicative Conservation Laws: Extension of the Wigner-Araki-Yanase Theorem

The Wigner-Araki-Yanase (WAY) theorem shows that additive conservation laws limit the accuracy of measurements. Recently, various quantitative expressions have been found for quantum limits on measurements induced by additive conservation laws, and have been applied to the study of fundamental limits on quantum information processing. Here, we investigate generalizations of the WAY theorem to multiplicative conservation laws. The WAY theorem is extended to show that an observable not commuting with the modulus of, or equivalently the square of, a multiplicatively conserved quantity cannot be precisely measured. We also obtain a lower bound for the mean-square noise of a measurement in the presence of a multiplicatively conserved quantity. To overcome this noise it is necessary to make large the coefficient of variation (the so-called relative fluctuation), instead of the variance as is the case for additive conservation laws, of the conserved quantity in the apparatus.Comment: 8 pages, REVTEX; typo added, to appear in PR

Large Predicted Self-Field Critical Current Enhancements In Superconducting Strips Using Magnetic Screens

A transport current distribution over a wide superconducting sheet is shown to strongly change in a presence of bulk magnetic screens of a soft magnet with a high permeability. Depending on the geometry, the effect may drastically suppress or protect the Meissner state of the sheet through the enhancement or suppression of the edge barrier critical current. The total transport current in the magnetically screened Meissner state is expected to compete with the critical current of the flux-filled sheet only for samples whose critical current is initially essentially controlled by the edge barrier effect.Comment: 6 figure

Minimum Decision Cost for Quantum Ensembles

For a given ensemble of $N$ independent and identically prepared particles, we calculate the binary decision costs of different strategies for measurement of polarised spin 1/2 particles. The result proves that, for any given values of the prior probabilities and any number of constituent particles, the cost for a combined measurement is always less than or equal to that for any combination of separate measurements upon sub-ensembles. The Bayes cost, which is that associated with the optimal strategy (i.e., a combined measurement) is obtained in a simple closed form.Comment: 11 pages, uses RevTe

Further Evidence for the Invasion and Establishment of Pterois volitans (Teleostei: Scorpaenidae) Along the Atlantic Coast of the United States

We document the continues population expansion of red lionfish, Pterois volitans, the first documented successful introduction of an invasive marine fish species from the western Pacific to Atlantic coastal water of the United States. Red lionfish are indigenous to the Indo-Pacific and have apparently established one or more breeding population on reefs off the southeastern United States. Fifty-nine specimens, most presumably adult red lionfish, were documented or collected on live-bottom reefs North Carolina, South Caroline, and Florida, and on a manmade structure off Georgia. Observation/collection depths and bottom water temperatures for these fish ranged from 4-99 m and 13.8-24.4 o c, respectively. Eleven juvenile lionfish, believed to be expatriated from southeastern waters, were collected in estuaries along the coast of Long Island, NY, at depths of 0-5 m and water temperatures ranging from 13.8-16.5 oC. Twelve of the total 70 specimens collected or observed were positively identified as red lionfish. Based on histological assessment of gonad tissue, two reproductively-active males and one immature female were collected. The life history of red lionfish, especially their reproductive biology and food habits, should be investigated along the east coast of the US to determine the potential impacts of the species on ecosystems they have invaded

Numerical electrokinetics

A new lattice method is presented in order to efficiently solve the electrokinetic equations, which describe the structure and dynamics of the charge cloud and the flow field surrounding a single charged colloidal sphere, or a fixed array of such objects. We focus on calculating the electrophoretic mobility in the limit of small driving field, and systematically linearise the equations with respect to the latter. This gives rise to several subproblems, each of which is solved by a specialised numerical algorithm. For the total problem we combine these solvers in an iterative procedure. Applying this method, we study the effect of the screening mechanism (salt screening vs. counterion screening) on the electrophoretic mobility, and find a weak non-trivial dependence, as expected from scaling theory. Furthermore, we find that the orientation of the charge cloud (i. e. its dipole moment) depends on the value of the colloid charge, as a result of a competition between electrostatic and hydrodynamic effects.Comment: accepted for publication in Journal of Physics Condensed Matter (proceedings of the 2012 CODEF conference