115,430 research outputs found
Cooperative spontaneous emission from indistinguishable atoms in arbitrary motional quantum states
We investigate superradiance and subradiance of indistinguishable atoms with
quantized motional states, starting with an initial total state that factorizes
over the internal and external degrees of freedom of the atoms. Due to the
permutational symmetry of the motional state, the cooperative spontaneous
emission, governed by a recently derived master equation [F. Damanet et al.,
Phys. Rev. A 93, 022124 (2016)], depends only on two decay rates and
and a single parameter describing the
dipole-dipole shifts. We solve the dynamics exactly for atoms,
numerically for up to 30 atoms, and obtain the large--limit by amean-field
approach. We find that there is a critical difference that
depends on beyond which superradiance is lost. We show that exact
non-trivial dark states (i.e. states other than the ground state with vanishing
spontaneous emission) only exist for , and that those states
(dark when ) are subradiant when .Comment: 14 pages, 8 figure
Space Station Freedom solar array panels plasma interaction test facility
The Space Station Freedom Power System will make extensive use of photovoltaic (PV) power generation. The phase 1 power system consists of two PV power modules each capable of delivering 37.5 KW of conditioned power to the user. Each PV module consists of two solar arrays. Each solar array is made up of two solar blankets. Each solar blanket contains 82 PV panels. The PV power modules provide a 160 V nominal operating voltage. Previous research has shown that there are electrical interactions between a plasma environment and a photovoltaic power source. The interactions take two forms: parasitic current loss (occurs when the currect produced by the PV panel leaves at a high potential point and travels through the plasma to a lower potential point, effectively shorting that portion of the PV panel); and arcing (occurs when the PV panel electrically discharges into the plasma). The PV solar array panel plasma interaction test was conceived to evaluate the effects of these interactions on the Space Station Freedom type PV panels as well as to conduct further research. The test article consists of two active solar array panels in series. Each panel consists of two hundred 8 cm x 8 cm silicon solar cells. The test requirements dictated specifications in the following areas: plasma environment/plasma sheath; outgassing; thermal requirements; solar simulation; and data collection requirements
Anticoherence of spin states with point group symmetries
We investigate multiqubit permutation-symmetric states with maximal entropy
of entanglement. Such states can be viewed as particular spin states, namely
anticoherent spin states. Using the Majorana representation of spin states in
terms of points on the unit sphere, we analyze the consequences of a
point-group symmetry in their arrangement on the quantum properties of the
corresponding state. We focus on the identification of anticoherent states (for
which all reduced density matrices in the symmetric subspace are maximally
mixed) associated with point-group symmetric sets of points. We provide three
different characterizations of anticoherence, and establish a link between
point symmetries, anticoherence and classes of states equivalent through
stochastic local operations with classical communication (SLOCC). We then
investigate in detail the case of small numbers of qubits, and construct
infinite families of anticoherent states with point-group symmetry of their
Majorana points, showing that anticoherent states do exist to arbitrary order.Comment: 15 pages, 5 figure
Comparing supernova remnants around strongly magnetized and canonical pulsars
The origin of the strong magnetic fields measured in magnetars is one of the
main uncertainties in the neutron star field. On the other hand, the recent
discovery of a large number of such strongly magnetized neutron stars, is
calling for more investigation on their formation. The first proposed model for
the formation of such strong magnetic fields in magnetars was through
alpha-dynamo effects on the rapidly rotating core of a massive star. Other
scenarios involve highly magnetic massive progenitors that conserve their
strong magnetic moment into the core after the explosion, or a common envelope
phase of a massive binary system. In this work, we do a complete re-analysis of
the archival X-ray emission of the Supernova Remnants (SNR) surrounding
magnetars, and compare our results with all other bright X-ray emitting SNRs,
which are associated with Compact Central Objects (CCOs; which are proposed to
have magnetar-like B-fields buried in the crust by strong accretion soon after
their formation), high-B pulsars and normal pulsars. We find that emission
lines in SNRs hosting highly magnetic neutron stars do not differ significantly
in elements or ionization state from those observed in other SNRs, neither
averaging on the whole remnants, nor studying different parts of their total
spatial extent. Furthermore, we find no significant evidence that the total
X-ray luminosities of SNRs hosting magnetars, are on average larger than that
of typical young X-ray SNRs. Although biased by a small number of objects, we
found that for a similar age, there is the same percentage of magnetars showing
a detectable SNR than for the normal pulsar population.Comment: 16 pages, 5 figures, Accepted for publication in MNRA
Strong photon non-linearities and photonic Mott insulators
We show, that photon non-linearities in electromagnetically induced
transparency can be at least one order of magnitude larger than predicted in
all previous approaches. As an application we demonstrate that, in this regime
they give rise to very strong photon - photon interactions which are strong
enough to make an experimental realization of a photonic Mott insulator state
feasible in arrays of coupled ultra high-Q micro-cavities.Comment: minor changes, to appear in Phys. Rev. Let
Comment on: "Estimating the Hartree-Fock limit from finite basis set calculations" [Jensen F (2005) Theor Chem Acc 113:267]
We demonstrate that a minor modification of the extrapolation proposed by
Jensen [(2005): Theor Chem Acc 113:267] yields very reliable estimates of the
Hartree-Fock limit in conjunction with correlation consistent basis sets.
Specifically, a two-point extrapolation of the form
yields HF limits
with an RMS error of 0.1 millihartree using aug-cc-pVQZ and
aug-cc-pV5Z basis sets, and of 0.01 millihartree using aug-cc-pV5Z and
aug-cc-pV6Z basis sets.Comment: Theoretical Chemistry Accounts, in pres
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