6,307 research outputs found
Protecting subspaces by acting on the outside
Many quantum control tasks aim at manipulating the state of a quantum
mechanical system within a finite subspace of states. However, couplings to the
outside are often inevitable. Here we discuss strategies which keep the system
in the controlled subspace by applying strong interactions onto the outside.
This is done by drawing analogies to simple toy models and to the quantum Zeno
effect. Special attention is paid to the constructive use of dissipation in the
protection of subspaces.Comment: 16 pages, 10 figure
Heisenberg's uncertainty principle for simultaneous measurement of positive-operator-valued measures
A limitation on simultaneous measurement of two arbitrary positive operator
valued measures is discussed. In general, simultaneous measurement of two
noncommutative observables is only approximately possible. Following Werner's
formulation, we introduce a distance between observables to quantify an
accuracy of measurement. We derive an inequality that relates the achievable
accuracy with noncommutativity between two observables. As a byproduct a
necessary condition for two positive operator valued measures to be
simultaneously measurable is obtained.Comment: 7 pages, 1 figure. To appear in Phys. Rev.
Approximate joint measurement of qubit observables through an Arthur-Kelly type model
We consider joint measurement of two and three unsharp qubit observables
through an Arthur-Kelly type joint measurement model for qubits. We investigate
the effect of initial state of the detectors on the unsharpness of the
measurement as well as the post-measurement state of the system. Particular
emphasis is given on a physical understanding of the POVM to PVM transition in
the model and entanglement between system and detectors.Two approaches for
characterizing the unsharpness of the measurement and the resulting measurement
uncertainty relations are considered.The corresponding measures of unsharpness
are connected for the case where both the measurements are equally unsharp. The
connection between the POVM elements and symmetries of the underlying
Hamiltonian of the measurement interaction is made explicit and used to perform
joint measurement in arbitrary directions. Finally in the case of three
observables we derive a necessary condition for the approximate joint
measurement and use it show the relative freedom available when the observables
are non-orthogonal.Comment: 22 pages; Late
Cold Power Tests of the sc 325 MHz CH-Cavity
At the Institute for Applied Physics (IAP), Frankfurt University, a superconducting 325 MHz CH-Cavity has been designed, built and first tests have successfully been performed. The cavity is determined for a 11.4 AMeV, 10 mA ion beam at the GSI UNILAC. Consisting of 7 gaps this resonator is envisaged to deliver a gradient of 5 MV/m. Novel features of this structure are a compact design, low peak fields, improved surface processing and power coupling. Furthermore a tuner system based on bellow tuners driven by a stepping motor and a piezo actuator and attached inside the resonator will control the frequency. In this contribution measurements executed at 4 K and 2 K at the cryo lab in Frankfurt will be presented
Simultaneous measurement of two non-commuting quantum variables: Solution of a dynamical model
The possibility of performing simultaneous measurements in quantum mechanics
is investigated in the context of the Curie-Weiss model for a projective
measurement. Concretely, we consider a spin- system simultaneously
interacting with two magnets, which act as measuring apparatuses of two
different spin components. We work out the dynamics of this process and
determine the final state of the measuring apparatuses, from which we can find
the probabilities of the four possible outcomes of the measurements. The
measurement is found to be non-ideal, as (i) the joint statistics do not
coincide with the one obtained by separately measuring each spin component, and
(ii) the density matrix of the spin does not collapse in either of the measured
observables. However, we give an operational interpretation of the process as a
generalised quantum measurement, and show that it is fully informative: The
expected value of the measured spin components can be found with arbitrary
precision for sufficiently many runs of the experiment.Comment: 24 pages, 9 figures; close to published versio
Measurement uncertainty relations
Measurement uncertainty relations are quantitative bounds on the errors in an
approximate joint measurement of two observables. They can be seen as a
generalization of the error/disturbance tradeoff first discussed heuristically
by Heisenberg. Here we prove such relations for the case of two canonically
conjugate observables like position and momentum, and establish a close
connection with the more familiar preparation uncertainty relations
constraining the sharpness of the distributions of the two observables in the
same state. Both sets of relations are generalized to means of order
rather than the usual quadratic means, and we show that the optimal constants
are the same for preparation and for measurement uncertainty. The constants are
determined numerically and compared with some bounds in the literature. In both
cases the near-saturation of the inequalities entails that the state (resp.
observable) is uniformly close to a minimizing one.Comment: This version 2 contains minor corrections and reformulation
Проектирование оборудования автоцистерны для применения в подразделениях добровольной пожарной охраны на базе специального автомобиля АРС-14
Актуальность данной работы заключается в том, что пожары с течением времени охватывают большую территорию и наносит значительный экономический ущерб сельским поселениям, удаленным на значительное расстояние от подразделений ФПС МЧС России. В связи с этим укомплектование добровольно пожарных команд ВДПО является решением данной проблемы. Целью данной работы является повышение эффективности ведения пожаротушения подразделениями ВДПО.The relevance of this work is that fires over time cover a large area and cause significant economic damage to rural settlements remote from a significant distance from the units of the Federal Emergency Service of Russia. In this regard, the manning of volunteer firefighters VDPO is the solution to this problem. The purpose of this work is to increase the efficiency of firefighting by VDPO units
Towards a more secure border control with 3D face recognition
Biometric data have been integrated in all ICAO compliant passports, since the ICAO members started to implement the ePassport standard. The additional use of three-dimensional models promises significant performance enhancements for border control points. By combining the geometry- and texture-channel information of the face, 3D face recognition systems show an improved robustness while processing variations in poses and problematic lighting conditions when taking the photo. This even holds in a hybrid scenario, when a 3D face scan is compared to a 2D reference image. To assess the potential of three-dimensional face recognition, the 3D Face project was initiated. This paper outlines the approach and research results of this project: The objective was not only to increase the recognition rate but also to develop a new, fake resistant capture device. In addition, methods for protection of the biometric template were researched and the second generation of the international standard ISO/IEC 19794-5:2011 was inspired by the project results
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