139,257 research outputs found
Universal Polarization
A method to polarize channels universally is introduced. The method is based
on combining two distinct channels in each polarization step, as opposed to
Arikan's original method of combining identical channels. This creates an equal
number of only two types of channels, one of which becomes progressively better
as the other becomes worse. The locations of the good polarized channels are
independent of the underlying channel, guaranteeing universality. Polarizing
the good channels further with Arikan's method results in universal polar codes
of rate 1/2. The method is generalized to construct codes of arbitrary rates.
It is also shown that the less noisy ordering of channels is preserved under
polarization, and thus a good polar code for a given channel will perform well
over a less noisy one.Comment: Submitted to the IEEE Transactions on Information Theor
Universal features of cell polarization processes
Cell polarization plays a central role in the development of complex
organisms. It has been recently shown that cell polarization may follow from
the proximity to a phase separation instability in a bistable network of
chemical reactions. An example which has been thoroughly studied is the
formation of signaling domains during eukaryotic chemotaxis. In this case, the
process of domain growth may be described by the use of a constrained
time-dependent Landau-Ginzburg equation, admitting scale-invariant solutions
{\textit{\`a la}} Lifshitz and Slyozov. The constraint results here from a
mechanism of fast cycling of molecules between a cytosolic, inactive state and
a membrane-bound, active state, which dynamically tunes the chemical potential
for membrane binding to a value corresponding to the coexistence of different
phases on the cell membrane. We provide here a universal description of this
process both in the presence and absence of a gradient in the external
activation field. Universal power laws are derived for the time needed for the
cell to polarize in a chemotactic gradient, and for the value of the smallest
detectable gradient. We also describe a concrete realization of our scheme
based on the analysis of available biochemical and biophysical data.Comment: Submitted to Journal of Statistical Mechanics -Theory and Experiment
A waveguide polarization toolset design based on mode beating
A toolset of waveguide elements is examined, which can be combined to produce polarization functional devices in a single contiguous waveguide. In particular, waveguide implementations of an optical isolator and a polarization modulator are discussed. The waveguide elements, i.e., quasi-phase-matched nonreciprocal polarization mode converter, reciprocal polarization mode converter (R-PMC), and a differential phase shifter, are all based on mode beating. A universal 3-dB R-PMC specification is identified, which suffices for all the polarization functional devices considered here. A full-vectorial modesolver is used to determine the modes in a number of example III–V waveguide structures, and the polarization state evolution is considered by using an averaged Stokes vector illustrated on the Poincaré sphere constr
Realization of the Optimal Universal Quantum Entangler
We present the first experimental demonstration of the ''optimal'' and
''universal'' quantum entangling process involving qubits encoded in the
polarization of single photons. The structure of the ''quantum entangling
machine'' consists of the quantum injected optical parametric amplifier by
which the contextual realization of the 1->2 universal quantum cloning and of
the universal NOT (U-NOT) gate has also been achieved.Comment: 10 pages, 3 figures, to appear in Physical Review
MUonE sensitivity to new physics explanations of the muon anomalous magnetic moment
The MUonE experiment aims at a precision measurement of the hadronic vacuum
polarization contribution to the muon , via elastic muon-electron
scattering. Since the current muon anomaly hints at the potential
existence of new physics (NP) related to the muon, the question then arises as
to whether the measurement of hadronic vacuum polarization in MUonE could be
affected by the same NP as well. In this work, we address this question by
investigating a variety of NP explanations of the muon anomaly via either
vector or scalar mediators with either flavor-universal, non-universal or even
flavor-violating couplings to electrons and muons. We derive the corresponding
MUonE sensitivity in each case and find that the measurement of hadronic vacuum
polarization at the MUonE is not vulnerable to any of these NP scenarios.Comment: 30 pages, 12 figures, minor corrections and changes, more references,
version to appear in JHE
Polarization Switching Dynamics Governed by Thermodynamic Nucleation Process in Ultrathin Ferroelectric Films
A long standing problem of domain switching process - how domains nucleate -
is examined in ultrathin ferroelectric films. We demonstrate that the large
depolarization fields in ultrathin films could significantly lower the
nucleation energy barrier (U*) to a level comparable to thermal energy (kBT),
resulting in power-law like polarization decay behaviors. The "Landauer's
paradox": U* is thermally insurmountable is not a critical issue in the
polarization switching of ultrathin ferroelectric films. We empirically find a
universal relation between the polarization decay behavior and U*/kBT.Comment: 5 pages, 4 figure
Anomalous resilient to decoherence macroscopic quantum superpositions generated by universally covariant optimal quantum cloning
We show that the quantum states generated by universal optimal quantum
cloning of a single photon represent an universal set of quantum superpositions
resilient to decoherence. We adopt Bures distance as a tool to investigate the
persistence ofquantum coherence of these quantum states. According to this
analysis, the process of universal cloning realizes a class of quantum
superpositions that exhibits a covariance property in lossy configuration over
the complete set of polarization states in the Bloch sphere.Comment: 8 pages, 6 figure
Quantum cloning with an optical fiber amplifier
It has been shown theoretically that a light amplifier working on the
physical principle of stimulated emission should achieve optimal quantum
cloning of the polarization state of light. We demonstrate close-to-optimal
universal quantum cloning of polarization in a standard fiber amplifier for
telecom wavelengths. For cloning 1 --> 2 we find a fidelity of 0.82, the
optimal value being 5/6 = 0.83.Comment: 4 pages, 3 figure
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