8,853 research outputs found
High Q Cavity Induced Fluxon Bunching in Inductively Coupled Josephson Junctions
We consider fluxon dynamics in a stack of inductively coupled long Josephson
junctions connected capacitively to a common resonant cavity at one of the
boundaries. We study, through theoretical and numerical analysis, the
possibility for the cavity to induce a transition from the energetically
favored state of spatially separated shuttling fluxons in the different
junctions to a high velocity, high energy state of identical fluxon modes.Comment: 8 pages, 5 figure
Geometric phases in open tripod systems
We first consider stimulated Raman adibatic passages (STIRAP) in a closed
four-level tripod system. In this case, the adiabatic eigenstates of the system
acquire real geometric phases. When the system is open and subject to
decoherence they acquire complex geometric phases that we determine by a Monte
Carlo wave function approach. We calculate the geometric phases and the state
evolution in the closed as well as in the open system cases and describe the
deviation between these in terms of the phases acquired. When the system is
closed, the adiabatic evolution implements a Hadamard gate. The open system
implements an imperfect gate and hence has a fidelity below unity. We express
this fidelity in terms of the acquired geometric phases.Comment: 10 pages 7 figure
Strong-field approximation for Coulomb explosion of H_2^+ by short intense laser pulses
We present a simple quantum mechanical model to describe Coulomb explosion of
H by short, intense, infrared laser pulses. The model is based on the
length gauge version of the molecular strong-field approximation and is valid
for pulses shorter than 50 fs where the process of dissociation prior to
ionization is negligible. The results are compared with recent experimental
results for the proton energy spectrum [I. Ben-Itzhak et al., Phys. Rev. Lett.
95, 073002 (2005), B. D. Esry et al., Phys. Rev. Lett. 97, 013003 (2006)]. The
predictions of the model reproduce the profile of the spectrum although the
peak energy is slightly lower than the observations. For comparison, we also
present results obtained by two different tunneling models for this process.Comment: 8 pages, 4 figure
Colour-singlet strangelets at finite temperature
Considering massless and quarks, and massive (150 MeV) quarks in
a bag with the bag pressure constant MeV, a colour-singlet
grand canonical partition function is constructed for temperatures
MeV. Then the stability of finite size strangelets is studied minimizing the
free energy as a function of the radius of the bag. The colour-singlet
restriction has several profound effects when compared to colour unprojected
case: (1) Now bulk energy per baryon is increased by about MeV making the
strange quark matter unbound. (2) The shell structures are more pronounced
(deeper). (3) Positions of the shell closure are shifted to lower -values,
the first deepest one occuring at , famous -particle ! (4) The shell
structure at vanishes only at MeV, though for higher
-values it happens so at MeV.Comment: Revtex file(8 pages)+6 figures(ps files) available on request from
first Autho
Magnetic field tuning and quantum interference in a Cooper pair splitter
Cooper pair splitting (CPS) is a process in which the electrons of naturally
occurring spin-singlet pairs in a superconductor are spatially separated using
two quantum dots. Here we investigate the evolution of the conductance
correlations in an InAs CPS device in the presence of an external magnetic
field. In our experiments the gate dependence of the signal that depends on
both quantum dots continuously evolves from a slightly asymmetric Lorentzian to
a strongly asymmetric Fano-type resonance with increasing field. These
experiments can be understood in a simple three - site model, which shows that
the nonlocal CPS leads to symmetric line shapes, while the local transport
processes can exhibit an asymmetric shape due to quantum interference. These
findings demonstrate that the electrons from a Cooper pair splitter can
propagate coherently after their emission from the superconductor and how a
magnetic field can be used to optimize the performance of a CPS device. In
addition, the model calculations suggest that the estimate of the CPS
efficiency in the experiments is a lower bound for the actual efficiency.Comment: 5 pages + 4 pages supplementary informatio
Einstein-Weyl structures and Bianchi metrics
We analyse in a systematic way the (non-)compact four dimensional
Einstein-Weyl spaces equipped with a Bianchi metric. We show that Einstein-Weyl
structures with a Class A Bianchi metric have a conformal scalar curvature of
constant sign on the manifold. Moreover, we prove that most of them are
conformally Einstein or conformally K\"ahler ; in the non-exact Einstein-Weyl
case with a Bianchi metric of the type or , we show that the
distance may be taken in a diagonal form and we obtain its explicit
4-parameters expression. This extends our previous analysis, limited to the
diagonal, K\"ahler Bianchi case.Comment: Latex file, 12 pages, a minor modification, accepted for publication
in Class. Quant. Gra
Kiloparsec-scale Spatial Offsets in Double-peaked Narrow-line Active Galactic Nuclei. I. Markers for Selection of Compelling Dual Active Galactic Nucleus Candidates
Merger-remnant galaxies with kpc-scale separation dual active galactic nuclei
(AGNs) should be widespread as a consequence of galaxy mergers and triggered
gas accretion onto supermassive black holes, yet very few dual AGNs have been
observed. Galaxies with double-peaked narrow AGN emission lines in the Sloan
Digital Sky Survey are plausible dual AGN candidates, but their double-peaked
profiles could also be the result of gas kinematics or AGN-driven outflows and
jets on small or large scales. To help distinguish between these scenarios, we
have obtained spatial profiles of the AGN emission via follow-up long-slit
spectroscopy of 81 double-peaked narrow-line AGNs in SDSS at 0.03 < z < 0.36
using Lick, Palomar, and MMT Observatories. We find that all 81 systems exhibit
double AGN emission components with ~kpc projected spatial separations on the
sky, which suggests that they are produced by kpc-scale dual AGNs or kpc-scale
outflows, jets, or rotating gaseous disks. In addition, we find that the
subsample (58%) of the objects with spatially compact emission components may
be preferentially produced by dual AGNs, while the subsample (42%) with
spatially extended emission components may be preferentially produced by AGN
outflows. We also find that for 32% of the sample the two AGN emission
components are preferentially aligned with the host galaxy major axis, as
expected for dual AGNs orbiting in the host galaxy potential. Our results both
narrow the list of possible physical mechanisms producing the double AGN
components, and suggest several observational criteria for selecting the most
promising dual AGN candidates from the full sample of double-peaked narrow-line
AGNs. Using these criteria, we determine the 17 most compelling dual AGN
candidates in our sample.Comment: 12 pages, 8 figures, published in ApJ. Modified from original version
to reflect referee's comment
Baryon Asymmetry, Dark Matter and Quantum Chromodynamics
We propose a novel scenario to explain the observed cosmological asymmetry
between matter and antimatter, based on nonperturbative QCD physics. This
scenario relies on a mechanism of separation of quarks and antiquarks in two
coexisting phases at the end of the cosmological QCD phase transition: ordinary
hadrons (and antihadrons), along with massive lumps (and antilumps) of novel
color superconducting phase. The latter would serve as the cosmological cold
dark matter. In certain conditions the separation of charge is C and CP
asymmetric and can leave a net excess of hadrons over antihadrons in the
conventional phase, even if the visible universe is globally baryon symmetric
. In this case an equal, but negative, overall baryon charge must be
hidden in the lumps of novel phase. Due to the small volume occupied by these
dense lumps/antilumps of color superconducting phase and the specific features
of their interaction with "normal" matter in hadronic phase, this scenario does
not contradict the current phenomenological constrains on presence of
antimatter in the visible universe. Moreover, in this scenario the observed
cosmological ratio within an order of magnitude
finds a natural explanation, as both contributions to originated from
the same physics during the QCD phase transition. The baryon to entropy ratio
would also be a natural outcome, fixed by the
temperature T_f \simlt T_{QCD} at which the separation of phases is
completed.Comment: New paragraph added in subsection II.D; version to appear in Physical
Review
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