5,853 research outputs found
Surprising relations between parametric level correlations and fidelity decay
Unexpected relations between fidelity decay and cross form--factor, i.e.,
parametric level correlations in the time domain are found both by a heuristic
argument and by comparing exact results, using supersymmetry techniques, in the
framework of random matrix theory. A power law decay near Heisenberg time, as a
function of the relevant parameter, is shown to be at the root of revivals
recently discovered for fidelity decay. For cross form--factors the revivals
are illustrated by a numerical study of a multiply kicked Ising spin chain.Comment: 4 pages 3 figure
Evolutionary Robotics: a new scientific tool for studying cognition
We survey developments in Artificial Neural Networks, in Behaviour-based Robotics and Evolutionary Algorithms that set the stage for Evolutionary Robotics in the 1990s. We examine the motivations for using ER as a scientific tool for studying minimal models of cognition, with the advantage of being capable of generating integrated sensorimotor systems with minimal (or controllable) prejudices. These systems must act as a whole in close coupling with their environments which is an essential aspect of real cognition that is often either bypassed or modelled poorly in other disciplines. We demonstrate with three example studies: homeostasis under visual inversion; the origins of learning; and the ontogenetic acquisition of entrainment
Die Wertschöpfungskette von Bio-Rübenzucker aus bayerischen Zuckerrüben und Nutzung des bayerischen Bio-Siegels
To foster the production of organic and local food the federal state of Bavaria introduced in 2015 the Bavarian organic label. Even though Bavaria has a comparatively high self-sufficiency in conventional sugar beet sugar there is a lack of organic sugar factories. In this study qualitative interviews have been conducted to analyze the value chain of organic sugar beets from Bavaria and the use of the organic and local label
Multiplicity at the Stellar/Substellar Boundary in Upper Scorpius
We present the results of a high-resolution imaging survey of 12 brown dwarfs
and very low mass stars in the closest (~145 pc) young (~5 Myr) OB association,
Upper Scorpius. We obtained images with the Advanced Camera for Surveys/High
Resolution Camera on HST through the F555W (V), F775W (i'), and F850LP (z')
filters. This survey discovered three new binary systems, including one
marginally resolved pair with a projected separation of only 4.9 AU, resulting
in an observed binary fraction of 25+/-14% at separations >4 AU. After
correcting for detection biases assuming a uniform distribution of mass ratios
for q>0.6, the estimated binary fraction is 33+/-17%. The binary fraction is
consistent with that inferred for higher-mass stars in Upper Sco, but the
separation and mass ratio distributions appear to be different. All three
low-mass binary systems in Upper Sco are tight (<18 AU) and of similar mass
(q>0.6), consistent with expectations based on previous multiplicity studies of
brown dwarfs and very low mass stars in the field and in open clusters. The
implication is that the distinct separation and mass ratio distributions of
low-mass systems are set in the formation process or at very young ages, rather
than by dynamical disruption of wide systems at ages >5 Myr. Finally, we
combine the survey detection limits with the models of Burrows et al. (1997) to
show that there are no planets or very low-mass brown dwarfs with masses >10
M_J at projected separations >20 AU, or masses >5 M_J at projected separations
>40 AU orbiting any of the low-mass (0.04-0.10 M_sun) objects in our sample.Comment: Accepted for publication in ApJ; 10 pages, 4 figures in emulateapj
forma
Exact diagonalisation of 1-d interacting spinless Fermions
We acquire a method of constructing an infinite set of exact eigenfunctions
of 1--d interacting spinless Fermionic systems. Creation and annihilation
operators for the interacting system are found and thereby the many--body
Hamiltonian is diagonalised. The formalism is applied to several examples. One
example is the theory of Jack polynomials. For the Calogero-Moser-Sutherland
Hamiltonian a direct proof is given that the asymptotic Bethe Ansatz is
correct.Comment: 33 page
Oscillatory decay of a two-component Bose-Einstein condensate
We study the decay of a two-component Bose-Einstein condensate with negative
effective interaction energy. With a decreasing atom number due to losses, the
atom-atom interaction becomes less important and the system undergoes a
transition from a bistable Josephson regime to the monostable Rabi regime,
displaying oscillations in phase and number. We study the equations of motion
and derive an analytical expression for the oscillation amplitude. A quantum
trajectory simulation reveals that the classical description fails for low
emission rates, as expected from analytical considerations. Observation of the
proposed effect will provide evidence for negative effective interaction.Comment: 4 pages, 3 figue
Limitation of entanglement due to spatial qubit separation
We consider spatially separated qubits coupled to a thermal bosonic field
that causes pure dephasing. Our focus is on the entanglement of two Bell states
which for vanishing separation are known as robust and fragile entangled
states. The reduced two-qubit dynamics is solved exactly and explicitly. Our
results allow us to gain information about the robustness of two-qubit
decoherence-free subspaces with respect to physical parameters such as
temperature, qubit-bath coupling strength and spatial separation of the qubits.
Moreover, we clarify the relation between single-qubit coherence and two-qubit
entanglement and identify parameter regimes in which the terms robust and
fragile are no longer appropriate.Comment: 7 pages, 3 figures; revised version, accepted for publication in
Europhys. Let
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