181 research outputs found
Conditions for complex spectra in a class of PT symmetric potentials
We study a wide class of solvable PT symmetric potentials in order to
identify conditions under which these potentials have regular solutions with
complex energy. Besides confirming previous findings for two potentials, most
of our results are new. We demonstrate that the occurrence of conjugate energy
pairs is a natural phenomenon for these potentials. We demonstrate that the
present method can readily be extended to further potential classes.Comment: 13 page
Universal measurement apparatus controlled by quantum software
We propose a quantum device that can approximate any projective measurement
on a qubit. The desired measurement basis is selected by the quantum state of a
"program register". The device is optimized with respect to maximal average
fidelity (assuming uniform distribution of measurement bases). An interesting
result is that if one uses two qubits in the same state as a program the
average fidelity is higher than if he/she takes the second program qubit in the
orthogonal state (with respect to the first one). The average information
obtainable by the proposed measurements is also calculated and it is shown that
it can get different values even if the average fidelity stays constant.
Possible experimental realization of the simplest proposed device is presented.Comment: 4 pages, 2 figures, reference adde
Optimal Planar Electric Dipole Antenna
Considerable time is often spent optimizing antennas to meet specific design
metrics. Rarely, however, are the resulting antenna designs compared to
rigorous physical bounds on those metrics. Here we study the performance of
optimized planar meander line antennas with respect to such bounds. Results
show that these simple structures meet the lower bound on radiation Q-factor
(maximizing single resonance fractional bandwidth), but are far from reaching
the associated physical bounds on efficiency. The relative performance of other
canonical antenna designs is compared in similar ways, and the quantitative
results are connected to intuitions from small antenna design, physical bounds,
and matching network design.Comment: 10 pages, 15 figures, 2 tables, 4 boxe
Experimental asymmetric phase-covariant quantum cloning of polarization qubits
We report on two optical realizations of the asymmetric
phase-covariant cloning machines for polarization states of single photons. The
experimental setups combine two-photon interference and tunable polarization
filtering that enables us to control the asymmetry of the cloners. The first
scheme involves a special unbalanced bulk beam splitter exhibiting different
splitting ratios for vertical and horizontal polarizations, respectively. The
second implemented scheme consists of a balanced fiber coupler where photon
bunching occurs, followed by a free-space part with polarization filters. With
this later approach we were able to demonstrate very high cloning fidelities
which are above the universal cloning limit.Comment: 7 pages, 8 figure
Interactions between planets and evolved stars
Searching for planetary companions to evolved stars (e.g., white dwarfs (WD) and Cataclysmic Variables (CV)) can provide insight into the interaction between planets and evolved stars as well as on the ultimate fate of planets. We have monitored decades of CVs and their progenitors including some detached WD binaries since 2006 to search for planets orbiting these systems. In the present paper, we will show some observational results of circumbinary planets in orbits around CVs and their progenitors. Some of our findings include planets with the shortest distance to the central evolved binaries and a few multiple planetary systems orbiting binary stars. Finally, by comparing the observational properties of planetary companions to single WDs and WD binaries, the interaction between planets and evolved stars and the ultimate fate of planets are discussed.Facultad de Ciencias AstronĂłmicas y GeofĂsicasInstituto de AstrofĂsica de La Plat
A New Species of \u3ci\u3eMyxidium\u3c/i\u3e (Myxosporea: Myxidiidae), from the Western Chorus Frog, \u3ci\u3ePseudacris triseriata triseriata\u3c/i\u3e, and Blanchard\u27s Cricket Frog, \u3ci\u3eAcris crepitans blanchardi\u3c/i\u3e (Hylidae), from Eastern Nebraska: Morphology, Phylogeny, and Critical Comments on Amphibian \u3ci\u3eMyxidium\u3c/i\u3e Taxonomy
During March 2001-April 2004, 164 adult anurans of 6 species (47 Rana blairi, 35 Rana catesbeiana, 31 Hyla chrysoscelis, 31 Pseudacris triseriata triseriata, 11 Bufo woodhousii, and 9 Acris crepitans blanchardi) from Pawnee Lake, Lancaster County, Nebraska, were surveyed for myxozoan parasites. Of these, 20 of 31 (65%) P. triseriata triseriata and 1 of 9 (11%) A. crepitans blanchardi were infected with a new species of Myxidium. Myxidium melleni n. sp. (Myxosporea) is described from the gallbladder of the western chorus frog, P. triseriata triseriata (Hylidae). This is the second species of Myxidium described from North American amphibians. Mature plasmodia are disc-shaped or elliptical 691 (400-1,375) Ă— 499 (230-1,200) Ă— 23 (16-35) ÎĽm, polysporic, producing many disporic pansporoblasts. The mature spores, 12.3 (12.0-13.5) Ă— 7.6 (7.0-9.0) Ă— 6.6 (6.0-8.0) ÎĽm, containing a single binucleated sporoplasm, are broadly elliptical, with 2-5 transverse grooves on each valve, and contain two equal polar capsules 5.2 (4.8-5.5) Ă— 4.2 (3.8-4.5) ÎĽm positioned at opposite ends of the spore. Myxidium melleni n. sp. is morphologically consistent with other members of Myxidium. However, M. melleni n. sp. was phylogenetically distinct from other Myxidium species for which DNA sequences are available. Only with improved morphological analyses, accompanied by molecular data, and the deposit of type specimens, can the ambiguous nature of Myxidium be resolved. Guidelines for descriptions of new species of Myxidium are provided
Scattering in the PT-symmetric Coulomb potential
Scattering on the -symmetric Coulomb potential is studied along a
U-shaped trajectory circumventing the origin in the complex plane from
below. This trajectory reflects symmetry, sets the appropriate
boundary conditions for bound states and also allows the restoration of the
correct sign of the energy eigenvalues. Scattering states are composed from the
two linearly independent solutions valid for non-integer values of the 2L
parameter, which would correspond to the angular momentum in the usual
Hermitian setting. Transmission and reflection coefficients are written in
closed analytic form and it is shown that similarly to other -symmetric scattering systems the latter exhibit handedness effect.
Bound-state energies are recovered from the poles of the transmission
coefficients.Comment: Journal of Physics A: Mathematical and Theoretical 42 (2009) to
appea
Quantum Big Bang without fine-tuning in a toy-model
The question of possible physics before Big Bang (or after Big Crunch) is
addressed via a schematic non-covariant simulation of the loss of observability
of the Universe. Our model is drastically simplified by the reduction of its
degrees of freedom to the mere finite number. The Hilbert space of states is
then allowed time-dependent and singular at the critical time . This
option circumvents several traditional theoretical difficulties in a way
illustrated via solvable examples. In particular, the unitary evolution of our
toy-model quantum Universe is shown interruptible, without any fine-tuning, at
the instant of its bang or collapse .Comment: 20 pp., 1 fig., invited talk for the conference "10th Workshop on
Quantization, Dualities and Integrable Systems" (April 22 - 24, 2011),
http://qdis.emu.edu.tr/index.htm
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