1,480 research outputs found
Continuous variable remote state preparation
We extend exact deterministic remote state preparation (RSP) with minimal
classical communication to quantum systems of continuous variables. We show
that, in principle, it is possible to remotely prepare states of an ensemble
that is parameterized by infinitely many real numbers, i.e., by a real
function, while the classical communication cost is one real number only. We
demonstrate continuous variable RSP in three examples using (i) quadrature
measurement and phase space displacement operations, (ii) measurement of the
optical phase and unitaries shifting the same, and (iii) photon counting and
photon number shift.Comment: 7 pages, RevTeX
Geometric phases for non-degenerate and degenerate mixed states
This paper focuses on the geometric phase of general mixed states under
unitary evolution. Here we analyze both non-degenerate as well as degenerate
states. Starting with the non-degenerate case, we show that the usual procedure
of subtracting the dynamical phase from the total phase to yield the geometric
phase for pure states, does not hold for mixed states. To this end, we furnish
an expression for the geometric phase that is gauge invariant. The parallelity
conditions are shown to be easily derivable from this expression. We also
extend our formalism to states that exhibit degeneracies. Here with the
holonomy taking on a non-abelian character, we provide an expression for the
geometric phase that is manifestly gauge invariant. As in the case of the
non-degenerate case, the form also displays the parallelity conditions clearly.
Finally, we furnish explicit examples of the geometric phases for both the
non-degenerate as well as degenerate mixed states.Comment: 23 page
Thermoacoustic tomography arising in brain imaging
We study the mathematical model of thermoacoustic and photoacoustic
tomography when the sound speed has a jump across a smooth surface. This models
the change of the sound speed in the skull when trying to image the human
brain. We derive an explicit inversion formula in the form of a convergent
Neumann series under the assumptions that all singularities from the support of
the source reach the boundary
Improvement of Surface Accuracy and Shop Floor Feed Rate Smoothing Through Open CNC Monitoring System and Cutting Simulation
AbstractIn the milling process of complex workpiece shapes the feed rate normally becomes instable due to the high degree of surface curvature that requires high acceleration and deceleration of the interpolated axes. This condition impacts on process time and on the surface accuracy regarding the manufactured part form and texture. The challenge to simulate the real machine and control behavior requires accurate models with a set of experiments to tune and dimension the model to the respective machine tool. The aim is to improve the HSC milling process of complex surfaces before removing any material. In this paper experiments show that the surface form accuracy and texture can be optimized through an automatic feed rate smoothing of the finishing operation directly on the machine tool. The axis positions and spindle speeds monitored through the open CNC are used as input for a geometric cutting simulation, thus enabling to predict and optimize the surface quality
Geometric observation for the Bures fidelity between two states of a qubit
In this Brief Report, we present a geometric observation for the Bures
fidelity between two states of a qubit.Comment: 4 pages, 1 figure, RevTex, Accepted by Phys. Rev.
Computationally efficient solutions for tracking people with a mobile robot: an experimental evaluation of Bayesian filters
Modern service robots will soon become an essential part of modern society. As they have to move and act in human environments, it is essential for them to be provided with a fast and reliable tracking system that localizes people in the neighbourhood. It is therefore important to select the most appropriate filter to estimate the position of these persons.
This paper presents three efficient implementations of multisensor-human tracking based on different Bayesian estimators: Extended Kalman Filter (EKF), Unscented Kalman Filter (UKF) and Sampling Importance Resampling (SIR) particle filter. The system implemented on a mobile robot is explained, introducing the methods used to detect and estimate the position of multiple people. Then, the solutions based on the three filters are discussed in detail. Several real experiments are conducted to evaluate their performance, which is compared in terms of accuracy, robustness and execution time of the estimation. The results show that a solution based on the UKF can perform as good as particle filters and can be often a better choice when computational efficiency is a key issue
Geometric Phases for Mixed States during Cyclic Evolutions
The geometric phases of cyclic evolutions for mixed states are discussed in
the framework of unitary evolution. A canonical one-form is defined whose line
integral gives the geometric phase which is gauge invariant. It reduces to the
Aharonov and Anandan phase in the pure state case. Our definition is consistent
with the phase shift in the proposed experiment [Phys. Rev. Lett. \textbf{85},
2845 (2000)] for a cyclic evolution if the unitary transformation satisfies the
parallel transport condition. A comprehensive geometric interpretation is also
given. It shows that the geometric phases for mixed states share the same
geometric sense with the pure states.Comment: 9 pages, 1 figur
Continuity and Stability of Partial Entropic Sums
Extensions of Fannes' inequality with partial sums of the Tsallis entropy are
obtained for both the classical and quantum cases. The definition of kth
partial sum under the prescribed order of terms is given. Basic properties of
introduced entropic measures and some applications are discussed. The derived
estimates provide a complete characterization of the continuity and stability
properties in the refined scale. The results are also reformulated in terms of
Uhlmann's partial fidelities.Comment: 9 pages, no figures. Some explanatory and technical improvements are
made. The bibliography is extended. Detected errors and typos are correcte
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