1,900 research outputs found
Entropy Distance: New Quantum Phenomena
We study a curve of Gibbsian families of complex 3x3-matrices and point out
new features, absent in commutative finite-dimensional algebras: a
discontinuous maximum-entropy inference, a discontinuous entropy distance and
non-exposed faces of the mean value set. We analyze these problems from various
aspects including convex geometry, topology and information geometry. This
research is motivated by a theory of info-max principles, where we contribute
by computing first order optimality conditions of the entropy distance.Comment: 34 pages, 5 figure
Strongly birefringent cut-wire pair structure as negative index wave plates at THz frequencies
We report a new approach for the design and fabrication of thin wave plates
with high transmission in the terahertz (THz) regime. The wave plates are based
on strongly birefringent cut-wire pair metamaterials that exhibit refractive
indices of opposite signs for two orthogonal polarization components of an
incident wave. As specific examples, we fabricated and investigated a quarter-
and a half-wave plate that revealed a peak intensity transmittance of 74% and
58% at 1.34 THz and 1.3 THz, respectively. Furthermore, the half wave plate
displayed a maximum figure of merit (FOM) of 23 at 1.3 THz where the refractive
index was -1.7. This corresponds to one of the highest FOMs reported at THz
frequencies so far. The presented results evidence that negative index
materials enter an application stage in terms of optical components for the THz
technology.Comment: 4 pages, 3 figures, submitted to Appl. Phys. Let
Optomechanically induced transparency
Coherent interaction of laser radiation with multilevel atoms and molecules
can lead to quantum interference in the electronic excitation pathways. A
prominent example observed in atomic three-level-systems is the phenomenon of
electromagnetically induced transparency (EIT), in which a control laser
induces a narrow spectral transparency window for a weak probe laser beam. The
concomitant rapid variation of the refractive index in this spectral window can
give rise to dramatic reduction of the group velocity of a propagating pulse of
probe light. Dynamic control of EIT via the control laser enables even a
complete stop, that is, storage, of probe light pulses in the atomic medium.
Here, we demonstrate optomechanically induced transparency (OMIT)--formally
equivalent to EIT--in a cavity optomechanical system operating in the resolved
sideband regime. A control laser tuned to the lower motional sideband of the
cavity resonance induces a dipole-like interaction of optical and mechanical
degrees of freedom. Under these conditions, the destructive interference of
excitation pathways for an intracavity probe field gives rise to a window of
transparency when a two-photon resonance condition is met. As a salient feature
of EIT, the power of the control laser determines the width and depth of the
probe transparency window. OMIT could therefore provide a new approach for
delaying, slowing and storing light pulses in long-lived mechanical excitations
of optomechanical systems, whose optical and mechanical properties can be
tailored in almost arbitrary ways in the micro- and nano-optomechanical
platforms developed to date
Cubic Defects: Comparing the Eight-State-System with its Two-Level-Approximation
Substitutional defects in a cubic symmetry (such as a lithium defect in a KCl
host crystal) can be modeled appropriately by an eight-state-system. Usually
this tunneling degree of freedom is approximated by a two-level-system. We
investigate the observable differences between the two models in three
contexts. First we show that the two models predict different relations between
the temperature dependence of specific heat and static susceptibility. Second
we demonstrate that in the presence of external forces (pressure and electric
field) the eight-state-system shows features that cannot be understood within
the framework of the two-level-approximation. In this context we propose an
experiment for measuring the parameter for tunneling along the face diagonal.
Finally we discuss the differences between the models appearing for strongly
coupled pairs. Geometric selection rules and particular forms of asymmetry lead
to clear differences between the two models.Comment: 19 pages, Latex, submitted to J. of Phys., some small supplement
Eta Carinae across the 2003.5 Minimum: Analysis in the visible and near infrared spectral region
We present an analysis of the visible through near infrared spectrum of Eta
Carinae and its ejecta obtained during the "Eta Carinae Campaign with the UVES
at the ESO VLT". This is a part of larger effort to present a complete Eta
Carinae spectrum, and extends the previously presented analyses with the
HST/STIS in the UV (1240-3159 A) to 10,430 A. The spectrum in the mid and near
UV is characterized by the ejecta absorption. At longer wavelengths, stellar
wind features from the central source and narrow emission lines from the
Weigelt condensations dominate the spectrum. However, narrow absorption lines
from the circumstellar shells are present. This paper provides a description of
the spectrum between 3060 and 10,430 A, including line identifications of the
ejecta absorption spectrum, the emission spectrum from the Weigelt
condensations and the P-Cygni stellar wind features. The high spectral
resolving power of VLT/UVES enables equivalent width measurements of atomic and
molecular absorption lines for elements with no transitions at the shorter
wavelengths. However, the ground based seeing and contributions of nebular
scattered radiation prevent direct comparison of measured equivalent widths in
the VLT/UVES and HST/STIS spectra. Fortunately, HST/STIS and VLT/UVES have a
small overlap in wavelength coverage which allows us to compare and adjust for
the difference in scattered radiation entering the instruments' apertures. This
paper provides a complete online VLT/UVES spectrum with line identifications
and a spectral comparison between HST/STIS and VLT/UVES between 3060 and 3160
A.Comment: 13 pages, 11 figures + atlas. The paper accepted for the ApJS and is
accompanied with an atlas in the online edition pape
Rotational levels in quantum dots
Low energy spectra of isotropic quantum dots are calculated in the regime of
low electron densities where Coulomb interaction causes strong correlations.
The earlier developed pocket state method is generalized to allow for
continuous rotations. Detailed predictions are made for dots of shallow
confinements and small particle numbers, including the occurance of spin
blockades in transport.Comment: RevTeX, 10 pages, 2 figure
Petrology and Geochemistry of Volcanic Rocks from the South Kauaʻi Swell Volcano, Hawaiʻi: Implications for the Lithology and Composition of the Hawaiian Mantle Plume
The South Kauaʻi Swell (SKS) volcano was sampled during four JASON dives and three dredge hauls recovering rocks that range from fresh pillow lavas to altered volcanic breccias. Two geochemical groups were identified: shield-stage tholeiites (5·4–3·9 Ma) and rejuvenation-stage alkalic lavas (1·9–0·1 Ma). The young SKS ages and the coeval rejuvenated volcanism along a 400km segment of the Hawaiian Islands (Maui to Niʻihau) are inconsistent with the timing and duration predictions by the flexure and secondary plume melting models for renewed volcanism. The SKS tholeiites are geochemically heterogeneous but similar to lavas from nearby Kauaʻi, Niʻihau and Waiʻanae volcanoes, indicating that their source regions within the Hawaiian mantle plume sampled a well-mixed zone. Most SKS tholeiitic lavas exhibit radiogenic Pb isotope ratios (208Pb*/206Pb*) that are characteristic of Loa compositions (>0·9475), consistent with the volcano’s location on the west side of the Hawaiian Islands. These results document the existence of the Loa component within the Hawaiian mantle plume prior to 5 Ma. Loa trend volcanoes are thought to have a major pyroxenite component in their source. Calculations of the pyroxenitic component in the parental melts for SKS tholeiites using high-precision olivine analyses and modeling of trace element ratios indicate a large pyroxenite proportion (≥50%), which was predicted by recent numerical models. Rejuvenation-stage lavas were also found to have a significant pyroxenite component based on olivine analyses (40–60%). The abundance of pyroxenite in the source for SKS lavas may be the cause of this volcano’s extended period of magmatism (>5 Myr). The broad distribution of the Loa component in the northern Hawaiian Island lavas coincides with the start of a dramatic magma flux increase (300%) along the Hawaiian Chain, which may reflect a major structural change in the source of the Hawaiian mantle plume
Continuity of the Maximum-Entropy Inference
We study the inverse problem of inferring the state of a finite-level quantum
system from expected values of a fixed set of observables, by maximizing a
continuous ranking function. We have proved earlier that the maximum-entropy
inference can be a discontinuous map from the convex set of expected values to
the convex set of states because the image contains states of reduced support,
while this map restricts to a smooth parametrization of a Gibbsian family of
fully supported states. Here we prove for arbitrary ranking functions that the
inference is continuous up to boundary points. This follows from a continuity
condition in terms of the openness of the restricted linear map from states to
their expected values. The openness condition shows also that ranking functions
with a discontinuous inference are typical. Moreover it shows that the
inference is continuous in the restriction to any polytope which implies that a
discontinuity belongs to the quantum domain of non-commutative observables and
that a geodesic closure of a Gibbsian family equals the set of maximum-entropy
states. We discuss eight descriptions of the set of maximum-entropy states with
proofs of accuracy and an analysis of deviations.Comment: 34 pages, 1 figur
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