17,889 research outputs found
Shear and Vorticity in a Combined Einstein-Cartan-Brans-Dicke Inflationary Lambda-Universe
A combined BCDE (Brans-Dicke and Einstein-Cartan) theory with lambda-term is
developed through Raychaudhuri's equation, for inflationary scenario. It
involves a variable cosmological constant, which decreases with time, jointly
with energy density, cosmic pressure, shear, vorticity, and Hubble's parameter,
while the scale factor, total spin and scalar field increase exponentially. The
post-inflationary fluid resembles a perfect one, though total spin grows, but
the angular speed does not (Berman, 2007d). Keywords: Cosmology; Einstein;
Brans-Dicke; Cosmological term; Shear; Spin; Vorticity; Inflation;
Einstein-Cartan; Torsion. PACS: 04.20.-q ; 98.80.-k ; 98.80.Bp ; 98.80.JkComment: 8 pages including front one. Published versio
A General Relativistic Rotating Evolutionary Universe
We show that when we work with coordinate cosmic time, which is not proper
time, Robertson-Walker's metric, includes a possible rotational state of the
Universe. An exact formula for the angular speed and the temporal metric
coefficient, is found.Comment: 5 pages including front cover. Publishe
Atomic entanglement generation with reduced decoherence via four-wave mixing
In most proposals for the generation of entanglement in large ensembles of
atoms via projective measurements, the interaction with the vacuum is
responsible for both the generation of the signal that is detected and the spin
depolarization or decoherence. In consequence, one has to usually work in a
regime where the information aquisition via detection is sufficiently slow
(weak measurement regime) such as not to strongly disturb the system. We
propose here a four-wave mixing scheme where, owing to the pumping of the
atomic system into a dark state, the polarization of the ensemble is not
critically affected by spontaneous emission, thus allowing one to work in a
strong measurement regime
Shear and Vorticity in Inflationary Brans-Dicke Cosmology with Lambda-Term
We find a solution for exponential inflation in Brans-Dicke cosmology endowed
with a cosmological term, which includes time-varying shear and vorticity. We
find that the scalar field and the scale factor increase exponentialy while
shear, vorticity, energy density, cosmic pressure and the cosmological term
decay exponentialy for beta < 0, where beta is defined in the text.Comment: 8 pages including front one. Published by Astrophysics and Space
Scienc
The Pioneer Anomaly and a Machian Universe
We discuss astronomical and astrophysical evidence, which we relate to the
principle of zero-total energy of the Universe, that imply several relations
among the mass M, the radius R and the angular momentum L of a "large" sphere
representing a Machian Universe. By calculating the angular speed, we find a
peculiar centripetal acceleration for the Universe. This is an ubiquituous
property that relates one observer to any observable. It turns out that this is
exactly the anomalous acceleration observed on the Pioneers spaceships. We have
thus, shown that this anomaly is to be considered a property of the Machian
Universe. We discuss several possible arguments against our proposal.Comment: 6 pages including front page. Publishe
Inflationary phase in Generalized Brans-Dicke theory
We find a solution for exponential inflation in a Brans-Dicke generalized
model, where the coupling "constant " is variable. While in General Relativity
the equation of state is p is equal to minus rho, here we find p proportional
to rho, where the proportionality constant is smaller than -2/3. The negativity
of cosmic pressure implies acceleration of the expansion, even with lambda < 0
>.Comment: International Journal of Theoretical Physics, to be publishe
Non-Resonant Effects in Implementation of Quantum Shor Algorithm
We simulate Shor's algorithm on an Ising spin quantum computer. The influence
of non-resonant effects is analyzed in detail. It is shown that our ``''-method successfully suppresses non-resonant effects even for relatively
large values of the Rabi frequency.Comment: 11 pages, 13 figure
Cooperative spin decoherence and population transfer
An ensemble of multilevel atoms is a good candidate for a quantum information
storage device. The information is encrypted in the collective ground state
atomic coherence, which, in the absence of external excitation, is decoupled
from the vacuum and therefore decoherence free. However, in the process of
manipulation of atoms with light pulses (writing, reading), one inadvertently
introduces a coupling to the environment, i.e. a source of decoherence. The
dissipation process is often treated as an independent process for each atom in
the ensemble, an approach which fails at large atomic optical depths where
cooperative effects must be taken into account. In this paper, the cooperative
behavior of spin decoherence and population transfer for a system of two,
driven multilevel-atoms is studied. Not surprisingly, an enhancement in the
decoherence rate is found, when the atoms are separated by a distance that is
small compared to an optical wavelength; however, it is found that this rate
increases even further for somewhat larger separations for atoms aligned along
the direction of the driving field's propagation vector. A treatment of the
cooperative modification of optical pumping rates and an effect of polarization
swapping between atoms is also discussed, lending additional insight into the
origin of the collective decay
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