7,117 research outputs found
Comment on "Classical interventions in quantum systems II. Relativistic invariance"
In a recent paper [Phys. Rev. A 61, 022117 (2000)], quant-ph/9906034, A.
Peres argued that quantum mechanics is consistent with special relativity by
proposing that the operators that describe time evolution do not need to
transform covariantly, although the measurable quantities need to transform
covariantly. We discuss the weaknesses of this proposal.Comment: 4 pages, to appear in Phys. Rev.
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
Coronal loop hydrodynamics. The solar flare observedon November 12 1980 revisited: the UV line emission
We revisit a well-studied solar flare whose X-ray emission originating from a
simple loop structure was observed by most of the instruments on board SMM on
November 12 1980. The X-ray emission of this flare, as observed with the XRP,
was successfully modeled previously. Here we include a detailed modeling of the
transition region and we compare the hydrodynamic results with the UVSP
observations in two EUV lines, measured in areas smaller than the XRP rasters,
covering only some portions of the flaring loop (the top and the foot-points).
The single loop hydrodynamic model, which fits well the evolution of coronal
lines (those observed with the XRP and the \FeXXI 1354.1 \AA line observed with
the UVSP) fails to model the flux level and evolution of the \OV 1371.3 \AA
line.Comment: A&A, in press, 6 pages, 5 figure
Bell's inequality with Dirac particles
We study Bell's inequality using the Bell states constructed from four
component Dirac spinors. Spin operator is related to the Pauli-Lubanski pseudo
vector which is relativistic invariant operator. By using Lorentz
transformation, in both Bell states and spin operator, we obtain an observer
independent Bell's inequality, so that it is maximally violated as long as it
is violated maximally in the rest frame.Comment: 7 pages. arXiv admin note: text overlap with arXiv:quant-ph/0308156
by other author
Mass Accretion Processes in Young Stellar Objects: Role of Intense Flaring Activity
According to the magnetospheric accretion scenario, young low-mass stars are
surrounded by circumstellar disks which they interact with through accretion of
mass. The accretion builds up the star to its final mass and is also believed
to power the mass outflows, which may in turn have a significant role in
removing the excess angular momentum from the star-disk system. Although the
process of mass accretion is a critical aspect of star formation, some of its
mechanisms are still to be fully understood. On the other hand, strong flaring
activity is a common feature of young stellar objects (YSOs). In the Sun, such
events give rise to perturbations of the interplanetary medium. Similar but
more energetic phenomena occur in YSOs and may influence the circumstellar
environment. In fact, a recent study has shown that an intense flaring activity
close to the disk may strongly perturb the stability of circumstellar disks,
thus inducing mass accretion episodes (Orlando et al. 2011). Here we review the
main results obtained in the field and the future perspectives.Comment: 4 pages, 2 Figures; accepted for publication on Acta Polytechnica
(Proceedings of the Frascati Workshop 2013
Minimal optimal generalized quantum measurements
Optimal and finite positive operator valued measurements on a finite number
of identically prepared systems have been presented recently. With physical
realization in mind we propose here optimal and minimal generalized quantum
measurements for two-level systems.
We explicitly construct them up to N=7 and verify that they are minimal up to
N=5. We finally propose an expression which gives the size of the minimal
optimal measurements for arbitrary .Comment: 9 pages, Late
A variant of Peres-Mermin proof for testing noncontextual realist models
For any state in four-dimensional system, the quantum violation of an
inequality based on the Peres-Mermin proof for testing noncontextual realist
models has experimentally been corroborated. In the Peres-Mermin proof, an
array of nine holistic observables for two two-qubit system was used. We, in
this letter, present a new symmetric set of observables for the same system
which also provides a contradiction of quantum mechanics with noncontextual
realist models in a state-independent way. The whole argument can also be cast
in the form of a new inequality that can be empirically tested.Comment: 3 pages, To be published in Euro. Phys. Let
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