2,564 research outputs found
Generalized uncertainty relations: Theory, examples, and Lorentz invariance
The quantum-mechanical framework in which observables are associated with
Hermitian operators is too narrow to discuss measurements of such important
physical quantities as elapsed time or harmonic-oscillator phase. We introduce
a broader framework that allows us to derive quantum-mechanical limits on the
precision to which a parameter---e.g., elapsed time---may be determined via
arbitrary data analysis of arbitrary measurements on identically prepared
quantum systems. The limits are expressed as generalized Mandelstam-Tamm
uncertainty relations, which involve the operator that generates displacements
of the parameter---e.g., the Hamiltonian operator in the case of elapsed time.
This approach avoids entirely the problem of associating a Hermitian operator
with the parameter. We illustrate the general formalism, first, with
nonrelativistic uncertainty relations for spatial displacement and momentum,
harmonic-oscillator phase and number of quanta, and time and energy and,
second, with Lorentz-invariant uncertainty relations involving the displacement
and Lorentz-rotation parameters of the Poincar\'e group.Comment: 39 pages of text plus one figure; text formatted in LaTe
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A multimedia tutorial shell with qualitative assessment in biology
The project is developing methods to produce multimedia tutorials relatively quickly and cheaply, using a generic software shell suitable for any subject area. The shell is a version of one produced originally as part of the HEFC-funded TLTP initiative by the Biodiversity Consortium. Tutorials presented in the shell will provide the student with a structured learning experience that will allow their initial knowledge level or their knowledge acquisition and progress to be qualitatively and quantitatively assessed. Where areas of weakness are revealed by the assessment, students will be advised to study particular parts of the tutorial in order to improve their understanding
Universal state inversion and concurrence in arbitrary dimensions
Wootters [Phys. Rev. Lett. 80, 2245 (1998)] has given an explicit formula for
the entanglement of formation of two qubits in terms of what he calls the
concurrence of the joint density operator. Wootters's concurrence is defined
with the help of the superoperator that flips the spin of a qubit. We
generalize the spin-flip superoperator to a "universal inverter," which acts on
quantum systems of arbitrary dimension, and we introduce the corresponding
concurrence for joint pure states of (D1 X D2) bipartite quantum systems. The
universal inverter, which is a positive, but not completely positive
superoperator, is closely related to the completely positive universal-NOT
superoperator, the quantum analogue of a classical NOT gate. We present a
physical realization of the universal-NOT superoperator.Comment: Revtex, 25 page
Quantum-mechanical model for continuous position measurements
We present an idealized model for a sequence of position measurements, and we then take an appropriate limit in which the measurements become continuous. The measurements lead to fluctuations without systematic dissipation, and they rapidly destroy off-diagonal terms in the position basis; thus the pointer basis is position. A modification of the model incorporates systematic dissipation via a feedback mechanism; in the modified model there is no decay of off-diagonal coherence in the position basis
Classical phase-space descriptions of continuous-variable teleportation
The nonnegative Wigner function of all quantum states involved in
teleportation of Gaussian states using the standard continuous-variable
teleportation protocol means that there is a local realistic phase-space
description of the process. This includes the coherent states teleported up to
now in experiments. We extend the phase-space description to teleportation of
non-Gaussian states using the standard protocol and conclude that teleportation
of non-Gaussian states with fidelity of 2/3 is a "gold standard" for this kind
of teleportation.Comment: New version contains minor changes requested by journal referee
Effect of machining parameters and cutting tool coating on hole quality in dry drilling of fibre metal laminates
Fibre metal laminates (FMLs) are a special type of hybrid materials, which consist of sheets of metallic alloys and prepregs of composite layers stacked together in an alternating sequence and bonded together either mechanically using micro hooks or thermally using adhesive epoxies. The present paper contributes to the current literature by studying the effects of three types of cutting tool coatings namely TiAlN, AlTiN/TiAlN and TiN on the surface roughness and burr formation of holes drilled in an FML commercially known as GLARE®. While the cutting tool geometry is fixed, the study is also conducted for a range of drilling conditions by varying the spindle speed and the feed rate. The obtained results indicate that the spindle speed and the type of cutting tool coating had the most significant influence on the achieved surface roughness metrics, while tool coating had the most significant effect on burr height and burr root thickness. The most important outcome for practitioners is that the best results in terms of minimum roughness and burr formation were obtained for the TiN coated drills. However, such drills outperform the other two types of tools, i.e. with TiAlN and AlTiN/TiAlN coatings, only when used for short series of hole drilling due to rapid tool deterioratio
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