163,361 research outputs found
Laser photon statistics in the feedback loop
A mere correspondence between the electron statistics and the photon one
vanishes in the feedback loop (FBL). It means that the direct photodetection,
supplying us with the electron statistics, does not provide us with a wished
information about the laser photon statistics. For getting this information we
should think up another measurement procedure, and we in the article suggest
applying the three-level laser as a auxiliary measuring device. This laser has
impressive property, namely, its photon statistics survive information about
the initial photon statistics of the laser which excites coherently the
three-level medium. Thus, if we choose the laser in the FBL as exciting the
three-level laser, then we have an possibility to evaluate its initial photon
statistics by means of direct detecting the three-level laser emission.
Finally, this approach allows us to conclude the feedback is not capable of
creating a regularity in the laser light beam. Contrary, the final photon
fluctuations turn out to be always even bigger. The mentioned above feature of
the three-level laser takes place only for the strong interaction between the
lasers (exciting and excited). It means the initial state of the exciting laser
is changed dramatically, so our measurement procedure can not be identified
with some non-demolition one.Comment: 12 pages, 3 figures, RevTeX4. Submitted to Journal of Optics
Magnetic fields of active galaxy nuclei and cosmological models
We present the review of various methods of detection of magnetic field
strengths in the nearest regions of the active galaxy nuclei (AGN) which are
the high energetic machines. Original spectropolarimetric method developed in
the Pulkovo Observatory allows us to determine the magnitude and geometry of
the magnetic field in the region of the optical and more hard electromagnetic
radiation. The results of theoretical calculations are compared to the results
of spectropolarimetric observations of AGN. We used the method of determining
magnetic fields through the spectrum synchrotron radiation in the region of
synchrotron self-absorption. As the magnitude of magnetic field of the
extragalactic source depends very strongly on the angular size of extragalactic
source and therefore on the photometric distance the calculated magnetic field
magnitudes depends very strongly on the definite cosmological model. This
result allows us to present the new method for determination of the most
important cosmological parameters including dark matter and dark energy
parameters.Comment: 8 pages, 7 figure
Magnetic Fields of Nearby Active Galactic Nuclei and Correlation of the Highest-Energy Cosmic Rays with their Positions
The correlation between the pointing direction of ultra high energy cosmic
rays and AGN observed by the Pierre Auger Collaboration is explained in the
framework of acceleration process in AGN. This acceleration process is produced
by a rotating accretion disk around a black hole that is frozen-in magnetic
field. In a result the accretion disk is acting as a induction accelerator of
cosmic rays. We estimate the resulting magnetic field in the framework of the
magnetic coupling process. The results of our calculations allow to make the
conclusion that the Flat Spectrum Radio Quasars appear the effective cosmic
accelerators. We estimate also the attenuation of highest-energy cosmic rays in
a result of their interaction with ambient radiation field.Comment: 5 page
Photon-Axion-Like Particle Coupling Constant and Cosmological Observations
We estimated the photon-pseudoscalar particle mixing constant from the effect
of cosmological alignment and cosmological rotation of polarization plane of
distant QSOs. This effect is explained in terms of birefringent phenomenon due
to photon-pseudoscalar (axion-like) particle mixing in a cosmic magnetic field.
On the contrary, one can estimate the strength of the cosmic magnetic field
using the constraints on the photon-axion-like particle coupling constant from
the CAST experiment and from SNe Ia dimming effect. In a result, the lower
limit on the intergalactic () magnetic field appears at the
level of about G.Comment: 8 page
Synchrotron Self-Absorption Process in GRBs and the Isotropic Energy - Peak Energy Fundamental Relation
The existence of strong correlation between the peak luminosity (and/or
bolometric energetics) of Gamma Ray Bursts (GRB) is one of the most intrigue
problem of GRB physics. This correlation is not yet understood. Here we
demonstrate that this correlation can be explained in framework of synchrotron
self-absorption (SSA) mechanism of GRB prompt emission. We estimate the
magnetic field strength of the central engine at the level , where is the Lorentz factor of fireball.Comment: 5 page
Theory optical excitation spectra and depolarization dynamics in bilayer WS from viewpoint of excimers
We investigate the optical excitation spectra and the photoluminescence
depolarization dynamics in bilayer WS. A different understanding of the
optical excitation spectra in the recent photoluminescence experimentby Zhu
{\em et al.} [arXiv:1403.6224] in bilayer WS is proposed. In the
experiment, four excitations (1.68, 1.93, 1.99 and 2.37 eV) are observed and
identified to be indirect exciton for the valley, trion, A exciton and
B exciton excitations, respectively, with the redshift for the A exciton energy
measured to be 3050 meV when the sample synthesized from monolayer to
bilayer. According to our study, by considering there exist both the
intra-layer and charge-transfer excitons in the bilayer WS, with
inter-layer hopping of the hole, there exists excimer state composed by the
superposition of the intra-layer and charge-transfer exciton states.
Accordingly, we show that the four optical excitations in the bilayer WS
are the A charge-transfer exciton, excimer, excimer and B
intra-layer exciton states, respectively, with the calculated resonance
energies showing good agreement with the experiment. In our picture, the
speculated indirect exciton, which involves a high-order phonon
absorption/emission process, is not necessary. Furthermore, the binding energy
for the excimer state is calculated to be 40 meV, providing reasonable
explanation for the experimentally observed energy redshift of the A exciton.
Based on the excimer states, we further derive the exchange interaction
Hamiltonian. Then the photoluminescence depolarization dynamics due to the
electron-hole exchange interaction is studied in the pump-probe setup by the
kinetic spin Bloch equations. We find that ......Comment: 14 pages, 2 figure
Gauge-invariant theory of optical response to THz pulses in s-wave and (+)-wave superconducting semiconductor quantum wells
We investigate the optical response to the THz pulses in the s-wave and
(+)-wave superconducting semiconductor quantum wells by using the
gauge-invariant optical Bloch equations, in which the gauge structure in the
superconductivity is explicitly retained. By using the gauge transformation,
not only can the microscopic description for the quasiparticle dynamics be
realized, but also the dynamics of the condensate is included, with the
superfluid velocity and the effective chemical potential naturally
incorporated. We reveal that the superfluid velocity itself can contribute to
the pump of quasiparticles (pump effect), with its rate of change acting as the
drive field to drive the quasiparticles (drive effect). Specifically, the drive
effect can contribute to the formation of the blocking region for the
quasiparticle, which directly suppresses the anomalous correlation of the
Cooper pairs. We find that both the pump and drive effects contribute to the
oscillations of the Higgs mode with twice the frequency of the optical field.
However, it is shown that the contribution from the drive effect to the
excitation of Higgs mode is dominant as long as the driven superconducting
momentum is less than the Fermi momentum. This is in contrast to the conclusion
from the Liouville or Bloch equations in the literature, in which the drive
effect on the anomalous correlation is overlooked with only the pump effect
considered.Furthermore, in the gauge-invariant optical Bloch equations, the
charge neutrality condition is {\em consistently} considered based on the
two-component model for the charge, in which the charge imbalance of
quasiparticles can cause the fluctuation of the effective chemical potential.
......Comment: 33 pages, 16 figure
Anomalous D'yakonov-Perel' spin relaxation in InAs (110) quantum wells under strong magnetic field: role of Hartree-Fock self-energy
We investigate the influence of the Hartree-Fock self-energy, acting as an
effective magnetic field, on the anomalous D'yakonov-Perel' spin relaxation in
InAs (110) quantum wells when the magnetic field in the Voigt configuration is
much stronger than the spin-orbit-coupled field. The transverse and
longitudinal spin relaxations are discussed both analytically and numerically.
For the transverse configuration, it is found that the spin relaxation is very
sensitive to the Hartree-Fock effective magnetic field, which is very different
from the conventional D'yakonov-Perel' spin relaxation. Even an extremely small
spin polarization () can significantly influence the behavior of the
spin relaxation. It is further revealed that this comes from the {\em unique}
form of the effective inhomogeneous broadening, originated from the mutually
perpendicular spin-orbit-coupled field and strong magnetic field. It is shown
that this effective inhomogeneous broadening is very small and hence very
sensitive to the Hartree-Fock field. Moreover, we further find that in the spin
polarization dependence, the transverse spin relaxation time decreases with the
increase of the spin polarization in the intermediate spin polarization regime,
which is also very different from the conventional situation, where the spin
relaxation is always suppressed by the Hartree-Fock field. It is revealed that
this {\em opposite} trends come from the additional spin relaxation channel
induced by the HF field. For the longitudinal configuration, we find that the
spin relaxation can be either suppressed or enhanced by the Hartree-Fock field
if the spin polarization is parallel or antiparallel to the magnetic field.Comment: 10 pages, 2 figure
Hot-electron effect in spin relaxation of electrically injected electrons in intrinsic Germanium
The hot-electron effect in the spin relaxation of electrically injected
electrons in intrinsic Germanium is investigated by the kinetic spin Bloch
equations both analytically and numerically. It is shown that in the
weak-electric-field regime with ~kV/cm, our calculations has
reasonable agreement with the recent transport experiment in the spin-injection
configuration [Phys. Rev. Lett. {\bf 111}, 257204 (2013)]. We reveal that the
spin relaxation is significantly enhanced at low temperature in the presence of
weak electric field ~V/cm, which originates from the obvious
center-of-mass drift effect due to the weak electron-phonon interaction,
whereas the hot-electron effect is demonstrated to be less important. This can
explain the discrepancy between the experimental observation and the previous
theoretical calculation [Phys. Rev. B {\bf 86}, 085202 (2012)], which deviates
from the experimental results by about two orders of magnitude at low
temperature. It is further shown that in the strong-electric-field regime with
~kV/cm, the spin relaxation is enhanced due to the
hot-electron effect, whereas the drift effect is demonstrated to be marginal.
Finally, we find that when ~kV/cm which lies in the
strong-electric-field regime, a small fraction of electrons ()
can be driven from the L to valley, and the spin relaxation rates are
the same for the and L valleys in the intrinsic sample without
impurity. With the negligible influence of the spin dynamics in the
valley to the whole system, the spin dynamics in the L valley can be measured
from the valley by the standard direct optical transition method.Comment: 10 pages, 3 figures, to be published in JPC
Gapped triplet -wave superconductivity in strong spin-orbit-coupled semiconductor quantum wells in proximity to -wave superconductor
We show that the {\it gapped} triplet superconductivity, i.e., a triplet
superconductor with triplet order parameter, can be realized in strong
spin-orbit-coupled quantum wells in proximity to -wave superconductor. It is
revealed that with the singlet order parameter induced from the superconducting
proximity effect, in quantum wells, not only can the triplet pairings arise due
to the spin-orbit coupling, but also the triplet order parameter can be induced
due to the repulsive effective electron-electron interaction, including the
electron-electron Coulomb and electron-phonon interactions. This is a natural
extension of the work of de Gennes, in which the repulsive-interaction-induced
singlet order parameter arises in the normal metal in proximity to -wave
superconductor [Rev. Mod. Phys. {\bf 36}, 225 (1964)]. Specifically, we derive
the effective Bogoliubov-de Gennes equation, in which the self-energies due to
the effective electron-electron interactions contribute to the singlet and
triplet order parameters. It is further shown that for the singlet order
parameter, it is efficiently suppressed due to this self-energy
renormalization; whereas for the triplet order parameter, it is the -wave
() one with the -vector parallel to the effective
magnetic field due to the spin-orbit coupling. Finally, we perform the
numerical calculation in InSb (100) quantum wells. Specifically, we reveal that
the Coulomb interaction is much more important than the electron-phonon
interaction at low temperature. Moreover, it shows that with proper electron
density, the minimum of the renormalized singlet and the maximum of the induced
triplet order parameters are comparable, and hence can be experimentally
distinguished.Comment: 15 pages, 8 figures, PRB in pres
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