2,194 research outputs found
An Analysis of Kinetic Response Variability
Studies evaluating variability of force as a function of absolute force generated are synthesized. Inconsistencies in reported estimates of this relationship are viewed as a function of experimental constraints imposed. Typically, within-subject force variability increases at a negative accelerating rate with equal increments in force produced. Current pulse-step and impulse variability models are unable to accommodate this description, although the notion of efficiency is suggested as a useful construct to explain the description outlined
The Paradox of Compacts: final report to the Home Office on monitoring the impact of Compacts
The Compact is an important building block in achieving a better relationship between
Government and the voluntary and community sector. We are fully committed to partnership
working with the sector and increasing their role in civil society and in the delivery of public
s e rvices. The Compact helps us to work better together, so that we can better meet the
needs of communities
Constrained bounds on measures of entanglement
Entanglement measures constructed from two positive, but not completely
positive maps on density operators are used as constraints in placing bounds on
the entanglement of formation, the tangle, and the concurrence of 4 x N mixed
states. The maps are the partial transpose map and the -map introduced by
Breuer [H.-P. Breuer, Phys. Rev. Lett. 97, 080501 (2006)]. The norm-based
entanglement measures constructed from these two maps, called negativity and
-negativity, respectively, lead to two sets of bounds on the entanglement
of formation, the tangle, and the concurrence. We compare these bounds and
identify the sets of 4 x N density operators for which the bounds from one
constraint are better than the bounds from the other. In the process, we
present a new derivation of the already known bound on the concurrence based on
the negativity. We compute new bounds on the three measures of entanglement
using both the constraints simultaneously. We demonstrate how such doubly
constrained bounds can be constructed. We discuss extensions of our results to
bipartite states of higher dimensions and with more than two constraints.Comment: 28 pages, 12 figures. v2 simplified and generalized derivation of
main results; errors correcte
Classical model for bulk-ensemble NMR quantum computation
We present a classical model for bulk-ensemble NMR quantum computation: the
quantum state of the NMR sample is described by a probability distribution over
the orientations of classical tops, and quantum gates are described by
classical transition probabilities. All NMR quantum computing experiments
performed so far with three quantum bits can be accounted for in this classical
model. After a few entangling gates, the classical model suffers an exponential
decrease of the measured signal, whereas there is no corresponding decrease in
the quantum description. We suggest that for small numbers of quantum bits, the
quantum nature of NMR quantum computation lies in the ability to avoid an
exponential signal decrease.Comment: 14 pages, no figures, revte
On quantum coding for ensembles of mixed states
We consider the problem of optimal asymptotically faithful compression for
ensembles of mixed quantum states. Although the optimal rate is unknown, we
prove upper and lower bounds and describe a series of illustrative examples of
compression of mixed states. We also discuss a classical analogue of the
problem.Comment: 23 pages, LaTe
Local Realistic Model for the Dynamics of Bulk-Ensemble NMR Information Processing
We construct a local realistic hidden-variable model that describes the
states and dynamics of bulk-ensemble NMR information processing up to about 12
nuclear spins. The existence of such a model rules out violation of any Bell
inequality, temporal or otherwise, in present high-temperature, liquid-state
NMR experiments. The model does not provide an efficient description in that
the number of hidden variables grows exponentially with the number of nuclear
spins.Comment: REVTEX, 7 page
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