24,574 research outputs found
A consistent design procedure for supercritical airfoils in free air and a wind tunnel
A computational inverse procedure for transonic airfoils in which shapes are determined supporting prescribed pressure distributions is presented. The method uses the small disturbance equation and a consistent analysis-design differencing procedure at the airfoil surface. This avoids the intermediate analysis-design-analysis iterations. The effect of any openness at the trailing edge is taken onto account by adding an effective source term in the far field. The final results from a systematic expansion procedure which models the far field for solid, ideal slotted, and free jet tunnel walls are presented along with some design results for the associated boundary conditions and those for a free flight
Majorana spinors and extended Lorentz symmetry in four-dimensional theory
An extended local Lorentz symmetry in four-dimensional (4D) theory is
considered. A source of this symmetry is a group of general linear
transformations of four-component Majorana spinors GL(4,M) which is isomorphic
to GL(4,R) and is the covering of an extended Lorentz group in a 6D Minkowski
space M(3,3) including superluminal and scaling transformations. Physical
space-time is assumed to be a 4D pseudo-Riemannian manifold. To connect the
extended Lorentz symmetry in the M(3,3) space with the physical space-time, a
fiber bundle over the 4D manifold is introduced with M(3,3) as a typical fiber.
The action is constructed which is invariant with respect to both general 4D
coordinate and local GL(4,M) spinor transformations. The components of the
metric on the 6D fiber are expressed in terms of the 4D pseudo-Riemannian
metric and two extra complex fields: 4D vector and scalar ones. These extra
fields describe in the general case massive particles interacting with an extra
U(1) gauge field and weakly interacting with ordinary particles, i.e.
possessing properties of invisible (dark) matter.Comment: 24 page
Entangling microscopic defects via a macroscopic quantum shuttle
In the microscopic world, multipartite entanglement has been achieved with
various types of nanometer sized two-level systems such as trapped ions, atoms
and photons. On the macroscopic scale ranging from micrometers to millimeters,
recent experiments have demonstrated bipartite and tripartite entanglement for
electronic quantum circuits with superconducting Josephson junctions. It
remains challenging to bridge these largely different length scales by
constructing hybrid quantum systems. Doing this may allow for manipulating the
entanglement of individual microscopic objects separated by macroscopically
large distances in a quantum circuit. Here we report on the experimental
demonstration of induced coherent interaction between two intrinsic two-level
states (TLSs) formed by atomic-scale defects in a solid via a superconducting
phase qubit. The tunable superconducting circuit serves as a shuttle
communicating quantum information between the two microscopic TLSs. We present
a detailed comparison between experiment and theory and find excellent
agreement over a wide range of parameters. We then use the theoretical model to
study the creation and movement of entanglement between the three components of
the quantum system.Comment: 11 pages, 5 figure
Measuring the temperature dependence of individual two-level systems by direct coherent control
We demonstrate a new method to directly manipulate the state of individual
two-level systems (TLS) in phase qubits. It allows one to characterize the
coherence properties of TLS using standard microwave pulse sequences, while the
qubit is used only for state readout. We apply this method to measure the
temperature dependence of TLS coherence for the first time. The energy
relaxation time is found to decrease quadratically with temperature for
the two TLS studied in this work, while their dephasing time measured in Ramsey
and spin-echo experiments is found to be limited at all temperatures.Comment: 4 pages, 5 figure
Observation of directly interacting coherent two-level systems in a solid
Parasitic two-level tunneling systems originating from structural material
defects affect the functionality of various microfabricated devices by acting
as a source of noise. In particular, superconducting quantum bits may be
sensitive to even single defects when these reside in the tunnel barrier of the
qubit's Josephson junctions, and this can be exploited to observe and
manipulate the quantum states of individual tunneling systems.
Here, we detect and fully characterize a system of two strongly interacting
defects using a novel technique for high-resolution spectroscopy. Mutual defect
coupling has been conjectured to explain various anomalies of glasses, and was
recently suggested as the origin of low frequency noise in superconducting
devices. Our study provides conclusive evidence of defect interactions with
full access to the individual constituents, demonstrating the potential of
superconducting qubits for studying material defects. All our observations are
consistent with the assumption that defects are generated by atomic tunneling.Comment: 13 pages, 7 figures. Includes supplementary materia
Quantitative evaluation of defect-models in superconducting phase qubits
We use high-precision spectroscopy and detailed theoretical modelling to
determine the form of the coupling between a superconducting phase qubit and a
two-level defect. Fitting the experimental data with our theoretical model
allows us to determine all relevant system parameters. A strong qubit-defect
coupling is observed, with a nearly vanishing longitudinal component. Using
these estimates, we quantitatively compare several existing theoretical models
for the microscopic origin of two-level defects.Comment: 3 pages, 2 figures. Supplementary material, lclimits_supp.pd
Emission of charged particles from excited compound nuclei
The formation of excited compound nucleus (CN) and its statistical decay is
investigated within the dinuclear system (DNS) model.The initial DNS is formed
in the entrance channel when the projectile is captured by a target, and then
the evolution of DNS in mass asymmetry coordinate leads to formation of the hot
CN. The emission barriers for complex fragments were calculated within the DNS
model by using the double folding procedure for the interaction potential. It
is shown that cross sections for complex fragment emission become larger when
excited CN is more neutron deficient. This approach gives also an opportunity
to calculate the new neutron deficient isotopes production cross sections and
can be applied to describe the hot fission of heavy systems.The model was
tested by comparison of calculated results with experimental dat
Resonant optical electron transfer in one-dimensional multiwell structures
We consider coherent single-electron dynamics in the one-dimensional
nanostructure under resonant electromagnetic pulse. The structure is composed
of two deep quantum wells positioned at the edges of structure and separated by
a sequence of shallow internal wells. We show that complete electron transfer
between the states localized in the edge wells through one of excited
delocalized states can take place at discrete set of times provided that the
pulse frequency matches one of resonant transition frequencies. The transfer
time varies from several tens to several hundreds of picoseconds and depends on
the structure and pulse parameters. The results obtained in this paper can be
applied to the developments of the quantum networks used in quantum
communications and/or quantum information processing.Comment: 25 pages,16 figure
Substructure Boosts to Dark Matter Annihilation from Sommerfeld Enhancement
The recently introduced Sommerfeld enhancement of the dark matter
annihilation cross section has important implications for the detection of dark
matter annihilation in subhalos in the Galactic halo. In addition to the boost
to the dark matter annihilation cross section from the high densities of these
subhalos with respect to the main halo, an additional boost caused by the
Sommerfeld enhancement results from the fact that they are kinematically colder
than the Galactic halo. If we further believe the generic prediction of CDM
that in each subhalo there is an abundance of substructure which is
approximately self-similar to that of the Galactic halo, then I show that
additional boosts coming from the density enhancements of these small
substructures and their small velocity dispersions enhance the dark matter
annihilation cross section even further. I find that very large boost factors
( to ) are obtained in a large class of models. The implications of
these boost factors for the detection of dark matter annihilation from dwarf
Spheroidal galaxies in the Galactic halo are such that, generically, they
outshine the background gamma-ray flux and are detectable by the Fermi
Gamma-ray Space Telescope.Comment: PRD in pres
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