2,437 research outputs found
Large negative and positive delay of optical pulses in coherently prepared dense Rb vapor with buffer gas
We experimentally study the group time delay for a light pulse propagating
through hot Rb vapor in the presence of a strong coupling field in a
configuration. We demonstrate that the ultra-slow pulse propagation is
transformed into superluminal propagation as the one-photon detuning of the
light increases due to the change in the transmission resonance lineshape.
Negative group velocity as low as -c/10^6=-80 m/s is recorded. We also find
that the advance time in the regime of the superluminal propagation grows
linearly with increasing laser field power.Comment: 5 pages, 6 figure
Representations of sl(2,?) in category O and master symmetries
We show that the indecomposable sl(2,?)-modules in the Bernstein-Gelfand-Gelfand category O naturally arise for homogeneous integrable nonlinear evolution systems. We then develop a new approach called the O scheme to construct master symmetries for such integrable systems. This method naturally allows computing the hierarchy of time-dependent symmetries. We finally illustrate the method using both classical and new examples. We compare our approach to the known existing methods used to construct master symmetries. For new integrable equations such as a Benjamin-Ono-type equation, a new integrable Davey-Stewartson-type equation, and two different versions of (2+1)-dimensional generalized Volterra chains, we generate their conserved densities using their master symmetries
Dynamical Model for Chemically Driven Running Droplets
We propose coupled evolution equations for the thickness of a liquid film and
the density of an adsorbate layer on a partially wetting solid substrate.
Therein, running droplets are studied assuming a chemical reaction underneath
the droplets that induces a wettability gradient on the substrate and provides
the driving force for droplet motion. Two different regimes for moving droplets
-- reaction-limited and saturated regime -- are described. They correspond to
increasing and decreasing velocities with increasing reaction rates and droplet
sizes, respectively. The existence of the two regimes offers a natural
explanation of prior experimental observations.Comment: 4 pages, 5 figure
Holography in 4D (Super) Higher Spin Theories and a Test via Cubic Scalar Couplings
The correspondences proposed previously between higher spin gauge theories
and free singleton field theories were recently extended into a more complete
picture by Klebanov and Polyakov in the case of the minimal bosonic theory in
D=4 to include the strongly coupled fixed point of the 3d O(N) vector model.
Here we propose an N=1 supersymmetric version of this picture. We also
elaborate on the role of parity in constraining the bulk interactions, and in
distinguishing two minimal bosonic models obtained as two different consistent
truncations of the minimal N=1 model that retain the scalar or the
pseudo-scalar field. We refer to these models as the Type A and Type B models,
respectively, and conjecture that the latter is holographically dual to the 3d
Gross-Neveu model. In the case of the Type A model, we show the vanishing of
the three-scalar amplitude with regular boundary conditions. This agrees with
the O(N) vector model computation of Petkou, thereby providing a non-trivial
test of the Klebanov-Polyakov conjecture.Comment: 30p
Analysis of the conduction mechanism through InSb quantum dot by tunnel CVC method
This work was supported by grants from the Russian Foundation for Basic Research Projects No. 16-07-00093 and No. 16-07-00185
Currents in a many-particle parabolic quantum dot under a strong magnetic field
Currents in a few-electron parabolic quantum dot placed into a perpendicular
magnetic field are considered. We show that traditional ways of investigating
the Wigner crystallization by studying the charge density correlation function
can be supplemented by the examination of the density-current correlator.
However, care must be exercised when constructing the correct projection of the
multi-dimensional wave function space. The interplay between the magnetic field
and Euler-liquid-like behavior of the electron liquid gives rise to persistent
and local currents in quantum dots. We demonstrate these phenomena by collating
a quasi-classical theory valid in high magnetic fields and an exact numerical
solution of the many-body problem.Comment: Uses RevTeX4, figures included in the tex
On frequencies of small oscillations of some dynamical systems associated with root systems
In the paper by F. Calogero and author [Commun. Math. Phys. 59 (1978)
109-116] the formula for frequencies of small oscillations of the Sutherland
system ( case) was found. In present note the generalization of this
formula for the case of arbitrary root system is given.Comment: arxiv version is already officia
Magnetic field imaging with atomic Rb vapor
We demonstrate the possibility of dynamic imaging of magnetic fields using
electromagnetically induced transparency in an atomic gas. As an experimental
demonstration we employ an atomic Rb gas confined in a glass cell to image the
transverse magnetic field created by a long straight wire. In this arrangement,
which clearly reveals the essential effect, the field of view is about 2 x 2
mm^2 and the field detection uncertainty is 0.14 mG per 10 um x 10 um image
pixel.Comment: 4 pages, 3 figure
Nonlocal resistance and its fluctuations in microstructures of band-inverted HgTe/(Hg,Cd)Te quantum wells
We investigate experimentally transport in gated microsctructures containing
a band-inverted HgTe/Hg_{0.3}Cd_{0.7}Te quantum well. Measurements of nonlocal
resistances using many contacts prove that in the depletion regime the current
is carried by the edge channels, as expected for a two-dimensional topological
insulator. However, high and non-quantized values of channel resistances show
that the topological protection length (i.e. the distance on which the carriers
in helical edge channels propagate without backscattering) is much shorter than
the channel length, which is ~100 micrometers. The weak temperature dependence
of the resistance and the presence of temperature dependent reproducible
quasi-periodic resistance fluctuations can be qualitatively explained by the
presence of charge puddles in the well, to which the electrons from the edge
channels are tunnel-coupled.Comment: 8 pages, 4 figures, published versio
Plasma instability and amplification of electromagnetic waves in low-dimensional electron systems
A general electrodynamic theory of a grating coupled two dimensional electron
system (2DES) is developed. The 2DES is treated quantum mechanically, the
grating is considered as a periodic system of thin metal strips or as an array
of quantum wires, and the interaction of collective (plasma) excitations in the
system with electromagnetic field is treated within the classical
electrodynamics. It is assumed that a dc current flows in the 2DES. We consider
a propagation of an electromagnetic wave through the structure, and obtain
analytic dependencies of the transmission, reflection, absorption and emission
coefficients on the frequency of light, drift velocity of 2D electrons, and
other physical and geometrical parameters of the system. If the drift velocity
of 2D electrons exceeds a threshold value, a current-driven plasma instability
is developed in the system, and an incident far infrared radiation is
amplified. We show that in the structure with a quantum wire grating the
threshold velocity of the amplification can be essentially reduced, as compared
to the commonly employed metal grating, down to experimentally achievable
values. Physically this is due to a considerable enhancement of the grating
coupler efficiency because of the resonant interaction of plasma modes in the
2DES and in the grating. We show that tunable far infrared emitters, amplifiers
and generators can thus be created at realistic parameters of modern
semiconductor heterostructures.Comment: 28 pages, 15 figures, submitted to Phys. Rev.
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