6,989 research outputs found
Quantum-Noise Power Spectrum of Fields with Discrete Classical Components
We present an algorithmic approach to calculate the quantum-noise spectral
density of photocurrents generated by optical fields with arbitrary discrete
classical spectrum in coherent or squeezed states. The measurement scheme may
include an arbitrary number of demodulations of the photocurrent. Thereby, our
method is applicable to the general heterodyne detection scheme which is
implemented in many experiments. For some of these experiments, e.g. in
laser-interferometric gravitational-wave detectors, a reliable prediction of
the quantum noise of fields in coherent and squeezed states plays a decisive
role in the design phase and detector characterization. Still, our
investigation is limited in two ways. First, we only consider coherent and
squeezed states of the field and second, we demand that the photocurrent
depends linearly on the field's vacuum amplitudes which means that at least one
of the classical components is comparatively strong.Comment: 8 pages, 2 figure
Optimal cloning for finite distributions of coherent states
We derive optimal cloning limits for finite Gaussian distributions of
coherent states, and describe techniques for achieving them. We discuss the
relation of these limits to state estimation and the no-cloning limit in
teleportation. A qualitatively different cloning limit is derived for a
single-quadrature Gaussian quantum cloner.Comment: 15 pages RevTeX, 6 figures eps, submitted to PR
Conditional two mode squeezed vacuum teleportation
We show, by making conditional measurements on the Einstein-Podolsky-Rosen
(EPR) squeezed vacuum, that one can improve the efficacy of teleportation for
both the position difference, momentum sum and number difference, phase sum
continuous variable teleportation protocols. We investigate the relative
abilities of the standard and conditional EPR states, and show that by
conditioning we can improve the fidelity of teleportation of coherent states
from below to above the boundary.Comment: 18 pages, RevTeX4, 10 figures postscrip
Teleportation using coupled oscillator states
We analyse the fidelity of teleportation protocols, as a function of resource
entanglement, for three kinds of two mode oscillator states: states with fixed
total photon number, number states entangled at a beam splitter, and the
two-mode squeezed vacuum state. We define corresponding teleportation protocols
for each case including phase noise to model degraded entanglement of each
resource.Comment: 21 pages REVTeX, manuscript format, 7 figures postscript, many
changes to pape
Effects of different vibration frequencies, amplitudes and contraction levels on lower limb muscles during graded isometric contractions superimposed on whole body vibration stimulation
Background: Indirect vibration stimulation, i.e., whole body vibration or upper limb vibration, has been investigated increasingly as an exercise intervention for rehabilitation applications. However, there is a lack of evidence regarding the effects of graded isometric contractions superimposed on whole body vibration stimulation. Hence, the objective of this study was to quantify and analyse the effects of variations in the vibration parameters and contraction levels on the neuromuscular responses to isometric exercise superimposed on whole body vibration stimulation. Methods: In this study, we assessed the 'neuromuscular effects' of graded isometric contractions, of 20%, 40%, 60%, 80% and 100% of maximum voluntary contraction, superimposed on whole body vibration stimulation (V) and control (C), i.e., no-vibration in 12 healthy volunteers. Vibration stimuli tested were 30 Hz and 50 Hz frequencies and 0.5 mm and 1.5 mm amplitude. Surface electromyographic activity of the vastus lateralis, vastus medialis and biceps femoris were measured during V and C conditions with electromyographic root mean square and electromyographic mean frequency values used to quantify muscle activity and their fatigue levels, respectively. Results: Both the prime mover (vastus lateralis) and the antagonist (biceps femoris) displayed significantly higher (P < 0.05) electromyographic activity with the V than the C condition with varying percentage increases in EMG root-mean-square (EMGrms) values ranging from 20% to 200%. For both the vastus lateralis and biceps femoris, the increase in mean EMGrms values depended on the frequency, amplitude and muscle contraction level with 50 Hz-0.5 mm stimulation inducing the largest neuromuscular activity. Conclusions: These results show that the isometric contraction superimposed on vibration stimulation leads to higher neuromuscular activity compared to isometric contraction alone in the lower limbs. The combination of the vibration frequency with the amplitude and the muscle tension together grades the final neuromuscular output.Peer reviewe
Restoration of Woodland Caribou to the Lake Superior Region
Woodland caribou (Rangifer tarandus caribou) historically occupied the boreal forest zone across the North American continent. The distribution and abundance of the species has declined in the past century. In particular, it has been extirpated from much of the southern limits of its historical range on both sides of the boundary between Canada and the United States (Bergerud 1974). Translocation of animals from extant populations may be used to reestablish populations in portions of the species\u27 former range. Recently, wildlife biologists in Ontario have translocated woodland caribou to a number of sites in or adjacent to Lake Superior. While it is too soon to evaluate their long-term success, these restoration efforts do provide useful insights into factors likely to influence the outcome of woodland caribou translocations elsewhere. In this chapter, we examine the 1) historical changes in range distribution, 2) natural history characteristics and requirements, and 3) results of recent translocations of woodland caribou, and use them to evaluate several alternative sites for possible woodland caribou restoration in the Lake Superior region. We also apply minimum viable population analysis to evaluate several translocation scenarios
Teleportation-based number state manipulation with number sum measurement
We examine various manipulations of photon number states which can be
implemented by teleportation technique with number sum measurement. The
preparations of the Einstein-Podolsky-Rosen resources as well as the number sum
measurement resulting in projection to certain Bell state may be done
conditionally with linear optical elements, i.e., beam splitters, phase
shifters and zero-one-photon detectors. Squeezed vacuum states are used as
primary entanglement resource, while single-photon sources are not required.Comment: 9 pages, 4 figures, Misprints are corrected. 3 figures for number sum
measurement are added. Discussion on manipulations are expanded. Calculations
for success probabilities are added. Fig.4 is adde
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