487 research outputs found
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
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
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
Three-photon states in nonlinear crystal superlattices
It has been a longstanding goal in quantum optics to realize controllable
sources generating joint multiphoton states, particularly, photon triplet with
arbitrary spectral characteristics. We demonstrate that such sources can be
realized via cascaded parametric down-conversion (PDC) in superlattice
structures of nonlinear and linear segments. We consider scheme that involves
two parametric processes: ,
under pulsed pump and investigate
spontaneous creation of photon triplet as well as generation of high-intensity
mode in intracavity three-photon splitting. We show preparation of
Greenberger-Horne-Zeilinger polarization entangled states in cascaded type-II
and type-I PDC in framework of consideration dual-grid structure that involves
two periodically-poled crystals. We demonstrate the method of compensation of
the dispersive effects in non-linear segments by appropriately chosen linear
dispersive segments of superlattice for preparation heralded joint states of
two polarized photons. In the case of intracavity three-photon splitting, we
concentrate on investigation of photon-number distributions, third-order
photon-number correlation function as well as the Wigner functions. These
quantities are observed both for short interaction time intervals and in over
transient regime, when dissipative effects are essential.Comment: 15 pages, 6 figure
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