3,641 research outputs found
Lasing in Strong Coupling
An almost ideal thresholdless laser can be realized in the strong-coupling
regime of light-matter interaction, with Poissonian fluctuations of the field
at all pumping powers and all intensities of the field. This ideal scenario is
thwarted by quantum nonlinearities when crossing from the linear to the
stimulated emission regime, resulting in a universal jump in the second order
coherence, which measurement could however be used to establish a standard of
lasing in strong coupling.Comment: 5 pages, 2 figure
Detection of Pulsed X-ray Emission from PSR B1706-44
We report the first detection of pulsed X-ray emission from the young,
energetic radio and Gamma-ray pulsar PSR B1706-44. We find a periodic signal at
a frequency of f = 9.7588088 +/- 0.0000026 Hz (at epoch 51585.34104 MJD),
consistent with the radio ephemeris, using data obtained with the High
Resolution Camera on-board the Chandra X-ray Observatory}. The probability that
this detection is a chance occurrence is 3.5E-5 as judged by the Rayleigh test.
The folded light curve has a broad, single-peaked profile with a pulsed
fraction of 23% +/- 6%. This result is consistent the ROSAT PSPC upper limit of
< 18% after allowing for the ability of Chandra to resolve the pulsar from a
surrounding synchrotron nebula. We also fitted Chandra spectroscopic data on
PSR B1706-44, which require at least two components, e.g., a blackbody of
temperature T(infinity) between 1.51E6 K and 1.83E6 K and a power-law of Gamma
= 2.0 +/- 0.5. The blackbody radius at the nominal 2.5 kpc distance is only
R(infinity) = 3.6 +/- 0.9 km, indicating either a hot region on a cooler
surface, or the need for a realistic atmosphere model that would allow a lower
temperature and larger area. Because the power-law and blackbody spectra each
contribute more than 23% of the observed flux, it is not possible to decide
which component is responsible for the modulation in the spectrally unresolved
light curve.Comment: 6 pages, 4 figures, Latex, emulateapj. Published version. Includes an
updated radio ephemeris and presents the absolute radio/X-ray phase alignmen
Coplanar stripline antenna design for optically detected magnetic resonance on semiconductor quantum dots
We report on the development and testing of a coplanar stripline antenna that
is designed for integration in a magneto-photoluminescence experiment to allow
coherent control of individual electron spins confined in single self-assembled
semiconductor quantum dots. We discuss the design criteria for such a structure
which is multi-functional in the sense that it serves not only as microwave
delivery but also as electrical top gate and shadow mask for the single quantum
dot spectroscopy. We present test measurements on hydrogenated amorphous
silicon, demonstrating electrically detected magnetic resonance using the
in-plane component of the oscillating magnetic field created by the coplanar
stripline antenna necessary due to the particular geometry of the quantum dot
spectroscopy. From reference measurements using a commercial electron spin
resonance setup in combination with finite element calculations simulating the
field distribution in the structure, we obtain an average magnetic field of
~0.2mT at the position where the quantum dots would be integrated into the
device. The corresponding pi-pulse time of ~0.3us fully meets the requirements
set by the high sensitivity optical spin read-out scheme developed for the
quantum dot
Parameter-free Stark Broadening of Hydrogen Lines in DA White Dwarfs
We present new calculations for the Stark broadening of the hydrogen line
profiles in the dense atmospheres of white dwarf stars. Our improved model is
based on the unified theory of Stark broadening from Vidal, Cooper & Smith, but
it also includes non-ideal gas effects from the Hummer & Mihalas occupation
probability formalism directly inside the line profile calculations. This
approach improves upon previous calculations that relied on the use of an
ad-hoc free parameter to describe the dissolution of the line wing opacity in
the presence of high electric microfields in the plasma. We present here the
first grid of model spectra for hot Teff >~ 12,000 K DA white dwarfs that has
no free parameters. The atmospheric parameters obtained from optical and UV
spectroscopic observations using these improved models are shown to differ
substantially from those published in previous studies.Comment: 8 pages, 8 figures, to appear in Journal of Physics Conference
Proceedings for the 16th European White Dwarf Worksho
Solutions of the sDiff(2)Toda equation with SU(2) Symmetry
We present the general solution to the Plebanski equation for an H-space that
admits Killing vectors for an entire SU(2) of symmetries, which is therefore
also the general solution of the sDiff(2)Toda equation that allows these
symmetries. Desiring these solutions as a bridge toward the future for yet more
general solutions of the sDiff(2)Toda equation, we generalize the earlier work
of Olivier, on the Atiyah-Hitchin metric, and re-formulate work of Babich and
Korotkin, and Tod, on the Bianchi IX approach to a metric with an SU(2) of
symmetries. We also give careful delineations of the conformal transformations
required to ensure that a metric of Bianchi IX type has zero Ricci tensor, so
that it is a self-dual, vacuum solution of the complex-valued version of
Einstein's equations, as appropriate for the original Plebanski equation.Comment: 27 page
EUVE Observations of the Magnetic Cataclysmic Variable QQ Vulpeculae
We present simultaneous X-ray (lambda_peak ~ 44A) and EUV (lambda_peak = 89A)
light curves for the magnetic cataclysmic variable QQ Vulpeculae, obtained with
the EUVE satellite. We find that the unique shape of the X-ray light curve is
different from previously obtained X-ray light curves of QQ Vul and provides
evidence for two-pole accretion. Detailed examination of the photometric data
indicates that QQ Vul undergoes a stellar eclipse of the X-ray emitting region,
indicative of a high binary inclination. We discuss possible implications for
the nature of this system given the observed shape of its EUV and X-ray light
curves.Comment: 12 pages including 4 figures, accepted to PAS
Emitters of -photon bundles
We propose a scheme based on the coherent excitation of a two-level system in
a cavity to generate an ultrabright CW and focused source of quantum light that
comes in groups (bundles) of photons, for an integer tunable with the
frequency of the exciting laser. We define a new quantity, the \emph{purity} of
-photon emission, to describe the percentage of photons emitted in bundles,
thus bypassing the limitations of Glauber correlation functions. We focus on
the case and show that close to 100% of two-photon emission and
90% of three-photon emission is within reach of state of the art cavity QED
samples. The statistics of the bundles emission shows that various
regimes---from -photon lasing to -photon guns---can be realized. This is
evidenced through generalized correlation functions that extend the standard
definitions to the multi-photon level.Comment: Introduce the n-th order N-photon correlation functions. Reorganized
to emphasize the N-photon emitter, now extended to the antibunching regime,
rather than only coherent emission as previsoul
Highly Non-linear Excitonic Zeeman Spin-Splitting in Composition-Engineered Artificial Atoms
Non-linear Zeeman splitting of neutral excitons is observed in composition
engineered In(x)Ga(1-x)As self-assembled quantum dots and its microscopic
origin is explained. Eight-band k.p simulations, performed using realistic dot
parameters extracted from cross-sectional scanning tunneling microscopy, reveal
that a quadratic contribution to the Zeeman energy originates from a spin
dependent mixing of heavy and light hole orbital states in the dot. The dilute
In-composition (x<0.35) and large lateral size (40-50 nm) of the quantum dots
investigated is shown to strongly enhance the non-linear excitonic Zeeman gap,
providing a blueprint to enhance such magnetic non-linearities via growth
engineering
Finite Euler Hierarchies And Integrable Universal Equations
Recent work on Euler hierarchies of field theory Lagrangians iteratively
constructed {}from their successive equations of motion is briefly reviewed. On
the one hand, a certain triality structure is described, relating arbitrary
field theories, {\it classical\ts} topological field theories -- whose
classical solutions span topological classes of manifolds -- and
reparametrisation invariant theories -- generalising ordinary string and
membrane theories. On the other hand, {\it finite} Euler hierarchies are
constructed for all three classes of theories. These hierarchies terminate with
{\it universal\ts} equations of motion, probably defining new integrable
systems as they admit an infinity of Lagrangians. Speculations as to the
possible relevance of these theories to quantum gravity are also suggested.Comment: (replaces previous unprintable version corrupted mailer) 13 p.,
(Plain TeX), DTP-92/3
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