645 research outputs found
Exceptional points and lines and Dirac points and lines in magnetoactive cholesteric liquid crystals
We investigated the properties of cholesteric liquid crystals (CLCs) being in
external static magnetic field directed along the helix axis. We have shown
that in the case of the wavelength dependence of magneto-optic activity
parameter, and in the presence of absorption new features appear in the optics
of CLCs. We have shown that in this case new photonic band gaps (PBGs) appear.
This new PBG is sensitive to the polarization of the incident light. But if the
chirality sign of the polarization of the incident diffracting light for the
basic PBG (which exist also at the absence of external magnetic field) is
determined only by the chirality sign of the CLC helix, then for the second one
it is determined by the external magnetic field direction (i.e., on whether the
directions of the external magnetic field and the incident light are parallel,
or they are antiparallel). We have shown that in this case besides Dirac points
there appear also Dirac lines as well as exceptional points and exceptional
lines. And moreover, at some of these points and lines there appear the lines
or wide bands of magnetically induced transparency, on others a wide coherent
perfect absorption band appears that is insensitive to incident light
polarization. And finally on some points the same reflection, transmission and
absorption takes place for any polarization of incident light. This system can
be applied as tunable narrow-band or broad-band filters and mirrors, a highly
tunable broad/narrow-band coherent perfect absorber, transmitter, ideal optical
diode, and other devices.Comment: 14 pages, 9 figures. arXiv admin note: text overlap with
arXiv:2305.0923
Adiabatic tracking for photo- and magneto-association of Bose-Einstein condensates with Kerr nonlinearities
We develop the method of adiabatic tracking for photo- and
magneto-association of Bose-Einstein atomic condensates with models that
include Kerr type nonlinearities. We show that the inclusion of these terms can
produce qualitatively important modifications in the adiabatic dynamics, like
the appearance of bifurcations, in which the trajectory that is being tracked
loses its stability. As a consequence the adiabatic theorem does not apply and
the adiabatic transfer can be strongly degraded. This degradation can be
compensated by using fields that are strong enough compared with the values of
the Kerr terms. The main result is that, despite these potentially detrimental
features, there is always a choice of the detuning that leads to an efficient
adiabatic tracking, even for relatively weak fields
Expansions of the solutions of the biconfluent Heun equation in terms of incomplete Beta and Gamma functions
Starting from equations obeyed by functions involving the first or the second
derivatives of the biconfluent Heun function, we construct two expansions of
the solutions of the biconfluent Heun equation in terms of incomplete Beta
functions. The first series applies single Beta functions as expansion
functions, while the second one involves a combination of two Beta functions.
The coefficients of expansions obey four- and five-term recurrence relations,
respectively. It is shown that the proposed technique is potent to produce
series solutions in terms of other special functions. Two examples of such
expansions in terms of the incomplete Gamma functions are presente
New powerful outburst of the unusual young star V1318 Cyg S (LkH{\alpha} 225)
Young double star V1318 Cyg, which is associated with a small isolated
star-forming region around HAeBe star BD+40o4124, has very unusual photometric
and spectral behavior. We present results of photometric and spectroscopic
observations in the optical range. We carried out BVRI CCD photometric
observations of V1318 Cyg from 2015 Sept. to 2017 July. For the same period we
acquired medium- and low-resolution spectra. Observations were performed with
the 2.6 m telescope. We analyze the historical light curve for V1318 Cyg and
demonstrate that the southern component, V1318 Cyg S, after being rather bright
in the 1970s (V14 mag) started to lower its brightness and in 1990
became practically invisible in the optical. After its reappearance in the
second half of the 1990s the star started to become very slowly brighter.
Between 2006 and 2010 V1318 Cyg S started brightening more quickly, and in 2015
had become brighter by more than five magnitudes in visible light. Since this
time V1318 Cyg S has remained at this maximum. Its spectrum shows little
variability and consists of a mixture of emission and absorption lines, which
has allowed for estimates of its spectral type as early Ae, with obvious
evidence of matter outflow. We derive its current A(V) 7.2 and L = 750
L(sun) thus confirming that V1318 Cyg S should belong to the Herbig Ae stars,
making it, along with BD+40o4124 and V1686 Cyg, the third luminous young star
in the group. It is very probable that we observe V1318 Cyg S near the pole and
that the inclination of its dense and slow ( 100 km/s) outflow is low.
The unusual variability and other features of V1318 Cyg S make it difficult to
classify this star among known types of eruptive young stars. It could be an
extreme, higher-mass example of an EXor, or an object of intermediate class
between EXors and FUors, like V1647 Ori.Comment: 9 pages, 7 figure
Bistability and chaos at low-level of quanta
We study nonlinear phenomena of bistability and chaos at a level of few
quanta. For this purpose we consider a single-mode dissipative oscillator with
strong Kerr nonlinearity with respect to dissipation rate driven by a
monochromatic force as well as by a train of Gaussian pulses. The quantum
effects and decoherence in oscillatory mode are investigated on the framework
of the purity of states and the Wigner functions calculated from the master
equation. We demonstrate the quantum chaotic regime by means of a comparison
between the contour plots of the Wigner functions and the strange attractors on
the classical Poincar\'e section. Considering bistability at low-limit of
quanta, we analyze what is the minimal level of excitation numbers at which the
bistable regime of the system is displayed? We also discuss the formation of
oscillatory chaotic regime by varying oscillatory excitation numbers at ranges
of few quanta. We demonstrate quantum-interference phenomena that are assisted
hysteresis-cycle behavior and quantum chaos for the oscillator driven by the
train of Gaussian pulses as well as we establish the border of
classical-quantum correspondence for chaotic regimes in the case of strong
nonlinearities.Comment: 10 pages, 14 figure
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