32,472 research outputs found
Quantum communication via a continuously monitored dual spin chain
We analyze a recent protocol for the transmission of quantum states via a
dual spin chain [Burgarth and Bose, Phys. Rev. A 71, 052315 (2005)] under the
constraint that the receiver's measurement strength is finite. That is, we
consider the channel where the ideal, instantaneous and complete von Neumann
measurements are replaced with a more realistic continuous measurement. We show
that for optimal performance the measurement strength must be "tuned" to the
channel spin-spin coupling, and once this is done, one is able to achieve a
similar transmission rate to that obtained with ideal measurements. The spin
chain protocol thus remains effective under measurement constraints.Comment: 5 pages, revtex 4, 3 eps figure
Quantum measurement and the first law of thermodynamics: the energy cost of measurement is the work value of the acquired information
The energy cost of measurement is an interesting fundamental question, and
may have profound implications for quantum technologies. In the context of
Maxwell's demon, it is often stated that measurement has no minimum energy
cost, while information has a work value, even though these statements can
appear contradictory. However, as we elucidate, these statements do no refer to
the cost paid by the measuring device. Here we show that it is only when a
measuring device has access to a zero temperature reservoir - that is, never -
that the measurement requires no energy. All real measuring devices pay the
cost that a heat engine pays to obtain the work value of the information they
acquire.Comment: 4 pages, revtex4-1. v2: added a referenc
Rapid purification of quantum systems by measuring in a feedback-controlled unbiased basis
Rapid-purification by feedback --- specifically, reducing the mean impurity
faster than by measurement alone --- can be achieved by making the eigenbasis
of the density matrix to be unbiased relative to the measurement basis. Here we
further examine the protocol introduced by Combes and Jacobs [Phys.Rev.Lett.
{\bf 96}, 010504 (2006)] involving continuous measurement of the observable
for a -dimensional system. We rigorously re-derive the lower bound
on the achievable speed-up factor, and also an upper bound, namely
, for all feedback protocols that use measurements in unbiased bases.
Finally we extend our results to independent measurements on a register of
qubits, and derive an upper bound on the achievable speed-up factor that
scales linearly with .Comment: v2: published versio
The effective average tax burden in the European Union and the USA: a computer-based calculation and comparison with the model of the European tax analyzer
In this paper we present a computer-based model (so-called European Tax Analyzer) for the international computation and comparison of company tax burdens. The methodology follows the forward-looking concepts for the measurement of effective average tax rates (EATR) on the basis of a model-firm. The EATR is computed for investments generating economic rents (i.e. pure profits above the market interest rate). In contrast to the prevailing approaches for calculating EATR based on separate and isolate investment projects the model-firm approach allows to calculate EATR for more complex and realistic conditions that are relevant for the decision making. Due to its flexibility another important advantage of the model-firm approach is the possibility to include the most relevant and complex provisions of the tax codes (i.e. tax systems, taxes, tax rates, and tax bases). A concrete computation and comparison of the EATR of corporations and their shareholders in five different countries reveals the wide spread between the national EATR. Moreover, for the time series 1995-2000 it could be shown that the differences between the EATR have declined a little. In spite of this convergence, however, tax distortions of competition did not become significantly less. --Tax burden comparison,capital income taxation,tax competition,tax harmonization in Europe
Quantum error correction for continuously detected errors with any number of error channels per qubit
It was shown by Ahn, Wiseman, and Milburn [PRA {\bf 67}, 052310 (2003)] that
feedback control could be used as a quantum error correction process for errors
induced by weak continuous measurement, given one perfectly measured error
channel per qubit. Here we point out that this method can be easily extended to
an arbitrary number of error channels per qubit. We show that the feedback
protocols generated by our method encode logical qubits in physical
qubits, thus requiring just one more physical qubit than in the previous case.Comment: 4 page
Advancing Learner Autonomy in Tefl Via Collaborative Learning
Learner autonomy has been defined as \u27a capacity to control important aspects of one\u27s learning\u27(Benson, 2013, p. 852). In the teaching of additional languages, learner autonomy dates back at least to the 1970s. For instance, Trim, who was a leader in the teaching of additional languages in Europe, stated that a goal of language education was to:
make the process of language learning more democratic by providing the con- ceptual tools for the planning, construction and conduct of courses closely geared to the needs, motivations and characteristics of the learner and enabling him [sic] so far as possible to steer and control his own progress. (1978, p. 1
Work function determination of promising material for thermionic converters
The work done to fabricate Marchuk plasma discharge tubes for measurement of the cesiated emission of lanthanum hexaboride and thoriated tungsten electrodes is described. A photon counting pyrometer was completed and is to be calibrated with a gold standard
Experiments with a Model Water Tunnel
This report describes a model water tunnel built in 1928 by the NACA to investigate the possibility of using water tunnels for aerodynamic investigations at large scales. The model tunnel is similar to an open-throat wind tunnel, but uses water for the working fluid
Effective one-dimensional description of confined diffusion biased by a transverse gravitational force
Diffusion of point-like non interacting particles in a two-dimensional (2D)
channel of varying cross section is considered. The particles are biased by a
constant force in the transverse direction. We apply our recurrence mapping
procedure, which enables us to derive an effective one-dimensional (1D)
evolution equation, governing the 1D density of the particles in the channel.
In the limit of stationary flow, we arrive at an extended Fick-Jacobs equation,
corrected by an effective diffusion coefficient D(x), depending on the
longitudinal coordinate x. Our result is an approximate formula for D(x),
involving also influence of the transverse force. Our calculations are verified
on the stationary diffusion in a linear cone, which is exactly solvable.Comment: 10 pages, 7 figures, submitted in Phys. Rev.
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