27,410 research outputs found
Heat Conductivity of Polyatomic and Polar Gases and Gas Mixtures
Theory for calculating heat conductivity of polyatomic and polar gases and gas mixture
Non-Collinear Ferromagnetic Luttinger Liquids
The presence of electron-electron interactions in one dimension profoundly
changes the properties of a system. The separation of charge and spin degrees
of freedom is just one example. We consider what happens when a system
consisting of a ferromagnetic region of non-collinearity, i.e. a domain wall,
is coupled to interacting electrons in one-dimension (more specifically a
Luttinger liquid). The ferromagnetism breaks spin charge separation and the
presence of the domain wall introduces a spin dependent scatterer into the
problem. The absence of spin charge separation and the effects of the electron
correlations results in very different behaviour for the excitations in the
system and for spin-transfer-torque effects in this model.Comment: 6 pages, submitted to Journal of Physics: Conference Series for JEMS
201
Quadrature entanglement and photon-number correlations accompanied by phase-locking
We investigate quantum properties of phase-locked light beams generated in a
nondegenerate optical parametric oscillator (NOPO) with an intracavity
waveplate. This investigation continuous our previous analysis presented in
Phys.Rev.A 69, 05814 (2004), and involves problems of continuous-variable
quadrature entanglement in the spectral domain, photon-number correlations as
well as the signatures of phase-locking in the Wigner function. We study the
role of phase-localizing processes on the quantum correlation effects. The
peculiarities of phase-locked NOPO in the self-pulsing instability operational
regime are also cleared up. The results are obtained in both the
P-representation as a quantum-mechanical calculation in the framework of
stochastic equations of motion, and also by using numerical simulation based on
the method of quantum state diffusion.Comment: Subm. to PR
Conserved currents in gravitational models with quasi-invariant Lagrangians: Application to teleparallel gravity
Conservation laws in gravitational theories with diffeomorphism and local Lorentz symmetry are studied. Main attention is paid to the construction of conserved currents and charges associated with an arbitrary vector field that generates a diffeomorphism on the spacetime. We further generalize previous results for the case of gravitational models described by quasi-invariant Lagrangians, that is, Lagrangians that change by a total derivative under the action of the local Lorentz group. The general formalism is then applied to the teleparallel models, for which the energy and the angular momentum of a Kerr black hole are calculated. The subsequent analysis of the results obtained demonstrates the importance of the choice of the frame
Upper bound for the conductivity of nanotube networks
Films composed of nanotube networks have their conductivities regulated by
the junction resistances formed between tubes. Conductivity values are enhanced
by lower junction resistances but should reach a maximum that is limited by the
network morphology. By considering ideal ballistic-like contacts between
nanotubes we use the Kubo formalism to calculate the upper bound for the
conductivity of such films and show how it depends on the nanotube
concentration as well as on their aspect ratio. Highest measured conductivities
reported so far are approaching this limiting value, suggesting that further
progress lies with nanowires other than nanotubes.Comment: 3 pages, 1 figure. Minor changes. Accepted for publication in Applied
Physics Letter
Biased Random Access Codes
A Random Access Code (RAC) is a communication task in which the sender
encodes a random message into a shorter one to be decoded by the receiver so
that a randomly chosen character of the original message is recovered with some
probability. Both the message and the character to be recovered are assumed to
be uniformly distributed. In this paper, we extend this protocol by allowing
more general distributions of these inputs, which alters the encoding and
decoding strategies optimizing the protocol performance, either with classical
or quantum resources. We approach the problem of optimizing the performance of
these biased RACs with both numerical and analytical tools. On the numerical
front, we present algorithms that allow a numerical evaluation of the optimal
performance over both classical and quantum strategies and provide a Python
package designed to implement them, called RAC-tools. We then use this
numerical tool to investigate single-parameter families of biased RACs in the
and scenarios. For RACs in the
scenario, we derive a general upper bound for the cases in which the inputs are
not correlated, which coincides with the quantum value for and, in some
cases for . Moreover, it is shown that attaining this upper bound
self-tests pairs or triples of rank-1 projective measurements, respectively. An
analogous upper bound is derived for the value of RACs in the
scenario which is shown to be always attainable using mutually unbiased
measurements if the distribution of input strings is unbiased
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