14,092 research outputs found
Transport of quantum noise through random media
We present an experimental study of the propagation of quantum noise in a
multiple scattering random medium. Both static and dynamic scattering
measurements are performed: the total transmission of noise is related to the
mean free path for scattering, while the noise frequency correlation function
determines the diffusion constant. The quantum noise observables are found to
scale markedly differently with scattering parameters compared to classical
noise observables. The measurements are explained with a full quantum model of
multiple scattering
Substrate effects on quasiparticles and excitons in graphene nanoflakes
The effects of substrate on electronic and optical properties of triangular
and hexagonal graphene nanoflakes with armchair edges are investigated by using
a configuration interaction approach beyond double excitation scheme. The
quasiparticle correction to the energy gap and exciton binding energy are found
to be dominated by the long-range Coulomb interactions and exhibit similar
dependence on the dielectric constant of the substrate, which leads to a
cancellation of their contributions to the optical gap. As a result, the
optical gaps are shown to be insensitive to the dielectric environment and
unexpectedly close to the single-particle gaps.Comment: 4 pages, 4 figure
Single-input and single-output (SISO) controller reduction based on the -norm
This paper proposes a new method to solve the controller-reduction problem based on the -norm. This method uses a reduced-order closed-loop system to deduce reduced-order controllers. The problem of obtaining the required lower-order closed-loop system was formulated as an -norm optimization, and the conditions were provided for guaranteeing the internal stability and the existence of lower-order controllers from the obtained reduced-order closed-loop system. In addition, the particle swarm optimization and sequence linear programming were adopted to solve the resultant -norm optimization. Two numerical examples demonstrated the effectiveness of the proposed method
Finite-volume effects on octet-baryon masses in covariant baryon chiral perturbation theory
We study finite-volume effects on the masses of the ground-state octet
baryons using covariant baryon chiral perturbation theory (ChPT) up to
next-to-leading order by analyzing the latest lattice Quantum
ChromoDynamics (LQCD) results from the NPLQCD collaboration. Contributions of
virtual decuplet baryons are taken into account using the "consistent" coupling
scheme. We compare our results with those obtained from heavy baryon ChPT and
show that, although both approaches can describe well the lattice data, the
underlying physics is different: In HBChPT, virtual decuplet baryons play a
more important role than they do in covariant ChPT. This is because the virtual
octet baryon contributions to finite-volume corrections are larger in covariant
ChPT than in HBChPT, while the contributions of intermediate decuplet baryons
are smaller, because of relativistic effects. We observe that for the octet
baryon masses, at fixed () finite-volume corrections decrease
as approaches its physical value, provided that the strange quark mass
is at or close to its physical value, as in most LQCD setups.Comment: 15 pages, 5 figure
Anisotropic hole spins in single and coupled self-assembled quantum dots
Anisotropy of hole spins in single and coupled self-assembled InAs/GaAs quantum dots is studied theoretically by means of an effective bond-orbital method. Compared with isotropic electron spins within the growth plane, it is found that the hole spins, although with much smaller positive g factors, can be highly anisotropic in single quantum dots. It is shown that the in-plane anisotropy of the hole spins can even reverse its sign as the height of the dots varies. In vertically coupled quantum dots, the in-plane hole g factors become comparable to the electrons, almost one order of magnitude larger than those in the single dots. Our result agrees qualitatively with the recent experiment [S. A. Crooker et al., Phys. Rev. Lett. 104, 036601 (2010)].published_or_final_versio
Building a 3.5 m prototype interferometer for the Q & A vacuum birefringence experiment and high precision ellipsometry
We have built and tested a 3.5 m high-finesse Fabry-Perot prototype
inteferometer with a precision ellipsometer for the QED test and axion search
(Q & A) experiment. We use X-pendulum-double-pendulum suspension designs and
automatic control schemes developed by the gravitational-wave detection
community. Verdet constant and Cotton-Mouton constant of the air are measured
as a test. Double modulation with polarization modulation 100 Hz and
magnetic-field modulation 0.05 Hz gives 10^{-7} rad phase noise for a 44-minute
integration.Comment: This draft has been presented in the 5th Edoardo Amaldi Conference on
Gravitational Wave
Neutrino masses and mixings
We propose a novel theoretical understanding of neutrino masses and mixings,
which is attributed to the intrinsic vector-like feature of the regularized
Standard Model at short distances. We try to explain the smallness of Dirac
neutrino masses and the decoupling of the right-handed neutrino as a free
particle. Neutrino masses and mixing angles are completely related to each
other in the Schwinger-Dyson equations for their self-energy functions. The
solutions to these equations and a possible pattern of masses and mixings are
discussed.Comment: LaTex 11 page
Laser opacity in underdense preplasma of solid targets due to quantum electrodynamics effects
We investigate how next-generation laser pulses at 10 PW 200 PW interact
with a solid target in the presence of a relativistically underdense preplasma
produced by amplified spontaneous emission (ASE). Laser hole boring and
relativistic transparency are strongly restrained due to the generation of
electron-positron pairs and -ray photons via quantum electrodynamics
(QED) processes. A pair plasma with a density above the initial preplasma
density is formed, counteracting the electron-free channel produced by the hole
boring. This pair-dominated plasma can block the laser transport and trigger an
avalanche-like QED cascade, efficiently transfering the laser energy to
photons. This renders a 1--scalelength, underdense preplasma
completely opaque to laser pulses at this power level. The QED-induced opacity
therefore sets much higher contrast requirements for such pulse in solid-target
experiments than expected by classical plasma physics. Our simulations show for
example, that proton acceleration from the rear of a solid with a preplasma
would be strongly impaired.Comment: 5 figure
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