71,391 research outputs found
Entangled states of trapped ions allow measuring the magnetic field gradient of a single atomic spin
Using trapped ions in an entangled state we propose detecting a magnetic
dipole of a single atom at distance of a few m. This requires a
measurement of the magnetic field gradient at a level of about 10
Tesla/m. We discuss applications e.g. in determining a wide variation of
ionic magnetic moments, for investigating the magnetic substructure of ions
with a level structure not accessible for optical cooling and detection,and for
studying exotic or rare ions, and molecular ions. The scheme may also be used
for measureing spin imbalances of neutral atoms or atomic ensembles trapped by
optical dipole forces. As the proposed method relies on techniques well
established in ion trap quantum information processing it is within reach of
current technology.Comment: 4 pages, 2 fi
High performance forward swept wing aircraft
A high performance aircraft capable of subsonic, transonic and supersonic speeds employs a forward swept wing planform and at least one first and second solution ejector located on the inboard section of the wing. A high degree of flow control on the inboard sections of the wing is achieved along with improved maneuverability and control of pitch, roll and yaw. Lift loss is delayed to higher angles of attack than in conventional aircraft. In one embodiment the ejectors may be advantageously positioned spanwise on the wing while the ductwork is kept to a minimum
Two-dimensional higher-derivative gravity and conformal transformations
We consider the lagrangian in classical (=non-quantized)
two-dimensional fourth-order gravity and give new relations to Einstein's
theory with a non-minimally coupled scalar field. We distinguish between
scale-invariant lagrangians and scale-invariant field equations. is
scale-invariant for F = c_1 R\sp {k+1} and a divergence for . The
field equation is scale-invariant not only for the sum of them, but also for
. We prove this to be the only exception and show in which sense it
is the limit of \frac{1}{k} R\sp{k+1} as . More generally: Let be
a divergence and a scale-invariant lagrangian, then has a
scale-invariant field equation. Further, we comment on the known generalized
Birkhoff theorem and exact solutions including black holes.Comment: 16 pages, latex, no figures, [email protected], Class. Quant.
Grav. to appea
Precision Photometry for Q0957+561 Images A and B
Since the persuasive determination of the time-delay in Q0957+561, much
interest has centered around shifting and subtracting the A and B light-curves
to look for residuals due to microlensing. Solar mass objects in the lens
galaxy produce variations on timescales of decades, with amplitudes of a few
tenths of a magnitude, but MACHO's (with masses of order to
) produce variations at only the 5% level. To detect such small
variations, highly precise photometry is required.
To that end, we have used 200 observations over three nights to examine the
effects of seeing on the light-curves. We have determined that seeing itself
can be responsible for correlated 5% variations in the light-curves of A and B.
We have found, however, that these effects can be accurately removed, by
subtracting the light from the lens galaxy, and by correcting for cross
contamination of light between the closely juxtaposed A and B images. We find
that these corrections improve the variations due to seeing from 5% to a level
only marginally detectable over photon shot noise (0.5%).Comment: 21 Pages with 9 PostScript figures, AASTeX 4 (preprint style
Microscopic mechanism for the 1/8 magnetization plateau in SrCu_2(BO_3)_2
The frustrated quantum magnet SrCu_2(BO_3)_2 shows a remarkably rich phase
diagram in an external magnetic field including a sequence of magnetization
plateaux. The by far experimentally most studied and most prominent
magnetization plateau is the 1/8 plateau. Theoretically, one expects that this
material is well described by the Shastry-Sutherland model. But recent
microscopic calculations indicate that the 1/8 plateau is energetically not
favored. Here we report on a very simple microscopic mechanism which naturally
leads to a 1/8 plateau for realistic values of the magnetic exchange constants.
We show that the 1/8 plateau with a diamond unit cell benefits most compared to
other plateau structures from quantum fluctuations which to a large part are
induced by Dzyaloshinskii-Moriya interactions. Physically, such couplings
result in kinetic terms in an effective hardcore boson description leading to a
renormalization of the energy of the different plateaux structures which we
treat in this work on the mean-field level. The stability of the resulting
plateaux are discussed. Furthermore, our results indicate a series of stripe
structures above 1/8 and a stable magnetization plateau at 1/6. Most
qualitative aspects of our microscopic theory agree well with a recently
formulated phenomenological theory for the experimental data of SrCu_2(BO_3)_2.
Interestingly, our calculations point to a rather large ratio of the magnetic
couplings in the Shastry-Sutherland model such that non-perturbative effects
become essential for the understanding of the frustrated quantum magnet
SrCu_2(BO_3)_2.Comment: 24 pages, 24 figure
A search for transit timing variation
Photometric follow-ups of transiting exoplanets (TEPs) may lead to
discoveries of additional, less massive bodies in extrasolar systems. This is
possible by detecting and then analysing variations in transit timing of
transiting exoplanets. In 2009 we launched an international observing campaign,
the aim of which is to detect and characterise signals of transit timing
variation (TTV) in selected TEPs. The programme is realised by collecting data
from 0.6--2.2-m telescopes spread worldwide at different longitudes. We present
our observing strategy and summarise first results for WASP-3b with evidence
for a 15 Earth-mass perturber in an outer 2:1 orbital resonance.Comment: Poster contribution to Detection and Dynamics of Transiting
Exoplanets (Haute Provence Observatory Colloquium, 23-27 August 2010
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