4,471 research outputs found
Quantum Fidelity Decay of Quasi-Integrable Systems
We show, via numerical simulations, that the fidelity decay behavior of
quasi-integrable systems is strongly dependent on the location of the initial
coherent state with respect to the underlying classical phase space. In
parallel to classical fidelity, the quantum fidelity generally exhibits
Gaussian decay when the perturbation affects the frequency of periodic phase
space orbits and power-law decay when the perturbation changes the shape of the
orbits. For both behaviors the decay rate also depends on initial state
location. The spectrum of the initial states in the eigenbasis of the system
reflects the different fidelity decay behaviors. In addition, states with
initial Gaussian decay exhibit a stage of exponential decay for strong
perturbations. This elicits a surprising phenomenon: a strong perturbation can
induce a higher fidelity than a weak perturbation of the same type.Comment: 11 pages, 11 figures, to be published Phys. Rev.
The Effects of Symmetries on Quantum Fidelity Decay
We explore the effect of a system's symmetries on fidelity decay behavior.
Chaos-like exponential fidelity decay behavior occurs in non-chaotic systems
when the system possesses symmetries and the applied perturbation is not tied
to a classical parameter. Similar systems without symmetries exhibit
faster-than-exponential decay under the same type of perturbation. This
counter-intuitive result, that extra symmetries cause the system to behave in a
chaotic fashion, may have important ramifications for quantum error correction.Comment: 5 pages, 3 figures, to be published Phys. Rev. E Rapid Communicatio
Terrain Database Correlation Assessment Using an Open Source Tool
Configuring networked simulators for training military teams in a distributed
environment requires the usage of a set of terrain databases to represent the
same training area. The results of simulation exercises can be degraded if the
terrain databases are poorly correlated. A number of methodologies for
determining the correlation between terrain databaHowever, there are few
computational tools for this task and most of them were developed to address
government needs, have limited availability, and handle specific digital
formats. The goal of this paper is thus to present a novel open source tool
developed as part of an academic research project.Comment: 12 pages, I/ITSEC 201
Influence of detector motion in entanglement measurements with photons
We investigate how the polarization correlations of entangled photons
described by wave packets are modified when measured by moving detectors. For
this purpose, we analyze the Clauser-Horne-Shimony-Holt Bell inequality as a
function of the apparatus velocity. Our analysis is motivated by future
experiments with entangled photons designed to use satellites. This is a first
step towards the implementation of quantum information protocols in a global
scale
The Use and Development of Mathematics Within Creative Literature
This paper presents a study on the extent to which creative literature been used as a vessel to carry forward the development of mathematical thought. The role of mathematics as a driving force for literature is highlighted, and while many examples exist that clearly show an attempt to disperse mathematical ideas, with Lewis Carroll, OuLiPo and ancient poetry considered, the argument that the sole purpose of the writings was for the sake of mathematical development is not clear-cut
Collective tests for quantum nonlocality
Pairs of spin-1/2 particles are prepared in a Werner state (namely, a mixture
of singlet and random components). If the random component is large enough, the
statistical results of spin measurements that may be performed on each pair
separately can be reproduced by an algorithm involving local ``hidden''
variables. However, if several such pairs are tested simultaneously, a
violation of the Clauser-Horne-Shimony-Holt inequality may occur, and no local
hidden variable model is compatible with the results.Comment: 14 pages, LaTeX, 1 figure on separate pag
Redshifted X-rays from the material accreting onto TW Hya: evidence of a low-latitude accretion spot
High resolution spectroscopy, providing constraints on plasma motions and
temperatures, is a powerful means to investigate the structure of accretion
streams in CTTS. In particular, the accretion shock region, where the accreting
material is heated to temperatures of a few MK as it continues its inward bulk
motion, can be probed by X-ray spectroscopy. To attempt to detect for the first
time the motion of this X-ray-emitting post-shock material, we searched for a
Doppler shift in the deep Chandra/HETGS observation of the CTTS TW Hya. This
test should unveil the nature of this X-ray emitting plasma component in CTTS,
and constrain the accretion stream geometry. We searched for a Doppler shift in
the X-ray emission from TW Hya with two different methods, by measuring the
position of a selected sample of emission lines, and by fitting the whole TW
Hya X-ray spectrum, allowing the line-of-sight velocity to vary. We found that
the plasma at T~2-4 MK has a line-of-sight velocity of 38.3+/-5.1 km/s with
respect to the stellar photosphere. This result definitively confirms that this
X-ray-emitting material originates in the post-shock region, at the base of the
accretion stream, and not in coronal structures. The comparison of the observed
velocity along the line of sight, 38.3+/-5.1 km/s, with the inferred intrinsic
velocity of the post shock of TW Hya, v_post~110-120 km/s, indicates that the
footpoints of the accretion streams on TW Hya are located at low latitudes on
the stellar surface. Our results indicate that complex magnetic field
geometries, such as that of TW Hya, permit low-latitude accretion spots.
Moreover, since on TW Hya the redshift of the soft X-ray emission is very
similar to that of the narrow component of the CIV resonance doublet at 1550
Ang, as found by Ardila et al. (2013), then the plasma at 2-4 MK and that at
0.1 MK likely originate in the same post-shock regions.Comment: Accepted for publication in Astronomy & Astrophysics; 2nd version
after language editor corrections; 16 pages, 8 figures, 6 table
General implementation of all possible positive-operator-value measurements of single photon polarization states
Positive Operator Value Measures (POVMs) are the most general class of
quantum measurements. We propose a setup in which all possible POVMs of a
single photon polarization state (corresponding to all possible sets of
two-dimensional Kraus operators) can be implemented easily using linear optics
elements. This method makes it possible to experimentally realize any
projective orthogonal, projective non-orthogonal or non-projective sets of any
number of POVM operators. Furthermore our implementation only requires vacuum
ancillas, and is deterministic rather than probabilistic. Thus it realizes
every POVM with the correct set of output states. We give the settings required
to implement two different well-known non-orthogonal projective POVMs.Comment: 5 pages, newer version with minor addition
Minimum error discrimination problem for pure qubit states
The necessary and sufficient conditions for minimization of the generalized
rate error for discriminating among pure qubit states are reformulated in
terms of Bloch vectors representing the states. For the direct optimization
problem an algorithmic solution to these conditions is indicated. A solution to
the inverse optimization problem is given. General results are widely
illustrated by particular cases of equiprobable states and pure qubit
states given with different prior probabilities.Comment: English is corrected thanks to PRA edito
Optimal measurements for relative quantum information
We provide optimal measurement schemes for estimating relative parameters of
the quantum state of a pair of spin systems. We prove that the optimal
measurements are joint measurements on the pair of systems, meaning that they
cannot be achieved by local operations and classical communication. We also
demonstrate that in the limit where one of the spins becomes macroscopic, our
results reproduce those that are obtained by treating that spin as a classical
reference direction.Comment: 6 pages, 1 figure, published versio
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