1,454 research outputs found
Noncommutative Riemann Surfaces
We compactify M(atrix) theory on Riemann surfaces Sigma with genus g>1.
Following [1], we construct a projective unitary representation of pi_1(Sigma)
realized on L^2(H), with H the upper half-plane. As a first step we introduce a
suitably gauged sl_2(R) algebra. Then a uniquely determined gauge connection
provides the central extension which is a 2-cocycle of the 2nd Hochschild
cohomology group. Our construction is the double-scaling limit N\to\infty,
k\to-\infty of the representation considered in the Narasimhan-Seshadri
theorem, which represents the higher-genus analog of 't Hooft's clock and shift
matrices of QCD. The concept of a noncommutative Riemann surface Sigma_\theta
is introduced as a certain C^\star-algebra. Finally we investigate the Morita
equivalence.Comment: LaTeX, 1+14 pages. Contribution to the TMR meeting ``Quantum aspects
of gauge theories, supersymmetry and unification'', Paris 1-7 September 199
Phase locking a clock oscillator to a coherent atomic ensemble
The sensitivity of an atomic interferometer increases when the phase
evolution of its quantum superposition state is measured over a longer
interrogation interval. In practice, a limit is set by the measurement process,
which returns not the phase, but its projection in terms of population
difference on two energetic levels. The phase interval over which the relation
can be inverted is thus limited to the interval ; going beyond
it introduces an ambiguity in the read out, hence a sensitivity loss. Here, we
extend the unambiguous interval to probe the phase evolution of an atomic
ensemble using coherence preserving measurements and phase corrections, and
demonstrate the phase lock of the clock oscillator to an atomic superposition
state. We propose a protocol based on the phase lock to improve atomic clocks
under local oscillator noise, and foresee the application to other atomic
interferometers such as inertial sensors.Comment: 9 pages, 7 figure
Feedback control of trapped coherent atomic ensembles
We demonstrate how to use feedback to control the internal states of trapped
coherent ensembles of two-level atoms, and to protect a superposition state
against the decoherence induced by a collective noise. Our feedback scheme is
based on weak optical measurements with negligible back-action and coherent
microwave manipulations. The efficiency of the feedback system is studied for a
simple binary noise model and characterized in terms of the trade-off between
information retrieval and destructivity from the optical probe. We also
demonstrate the correction of more general types of collective noise. This
technique can be used for the operation of atomic interferometers beyond the
standard Ramsey scheme, opening the way towards improved atomic sensors.Comment: 9 pages, 6 figure
Trajectories in the Context of the Quantum Newton's Law
In this paper, we apply the one dimensional quantum law of motion, that we
recently formulated in the context of the trajectory representation of quantum
mechanics, to the constant potential, the linear potential and the harmonic
oscillator. In the classically allowed regions, we show that to each classical
trajectory there is a family of quantum trajectories which all pass through
some points constituting nodes and belonging to the classical trajectory. We
also discuss the generalization to any potential and give a new definition for
de Broglie's wavelength in such a way as to link it with the length separating
adjacent nodes. In particular, we show how quantum trajectories have as a limit
when the classical ones. In the classically forbidden regions,
the nodal structure of the trajectories is lost and the particle velocity
rapidly diverges.Comment: 17 pages, LateX, 6 eps figures, minor modifications, Title changed,
to appear in Physica Script
Ten years of Energy Efficiency: a bibliometric analysis
© 2018, Springer Nature B.V. Energy Efficiency is an international journal dedicated to research topics connected to energy with a focus on end-use efficiency issues. In 2018, the journal celebrates its 10th anniversary. In order to mark it and analyze not only how the journal has been performing over the years, but also which are the trends for academic debate and research in this journal, this article presents a bibliometric overview of the publication and citation structure of the journal during period 2008–2017. The study relies on the Web of Science Core Collection and the Scopus database to collect the bibliographic results. Additionally, the work exploits the visualization of similarities (VOS) viewer software to map graphically the bibliographic material. The research analyses the most cited papers and the most popular keywords. Moreover, the paper studies how the journal connects with other international journals and identifies the most productive authors, institutions, and countries. The results indicate that the journal has rapidly grown over the years, obtained a merited position in the scientific community, with contributions from authors all over the world (with Europe as the most productive region). Moreover, the journal has focused so far mainly on energy efficiency issues in close relationship with policies and incentives, corporate energy efficiency, consumer behavior, and demand-side management programs, with both industrial, building and transport sectors widely involved. Our discussion concludes with suggested future research avenues, in particular towards coordinated efforts from different disciplines (technical, economic, and sociopsychological ones) to address the emerging energy efficiency challenges
A Kiloparsec-Scale Hyper-Starburst in a Quasar Host Less than 1 Gigayear after the Big Bang
The host galaxy of the quasar SDSS J114816.64+525150.3 (at redshift z=6.42,
when the Universe was <1 billion years old) has an infrared luminosity of
2.2x10^13 L_sun, presumably significantly powered by a massive burst of star
formation. In local examples of extremely luminous galaxies such as Arp220, the
burst of star formation is concentrated in the relatively small central region
of <100pc radius. It is unknown on which scales stars are forming in active
galaxies in the early Universe, which are likely undergoing their initial burst
of star formation. We do know that at some early point structures comparable to
the spheroidal bulge of the Milky Way must have formed. Here we report a
spatially resolved image of [CII] emission of the host galaxy of
J114816.64+525150.3 that demonstrates that its star forming gas is distributed
over a radius of ~750pc around the centre. The surface density of the star
formation rate averaged over this region is ~1000 M_sun/yr/kpc^2. This surface
density is comparable to the peak in Arp220, though ~2 orders of magnitudes
larger in area. This vigorous star forming event will likely give rise to a
massive spheroidal component in this system.Comment: Nature, in press, Feb 5 issue, p. 699-70
Spin-squeezing and Dicke state preparation by heterodyne measurement
We investigate the quantum non-demolition (QND) measurement of an atomic
population based on a heterodyne detection and show that the induced
back-action allows to prepare both spin-squeezed and Dicke states. We use a
wavevector formalism to describe the stochastic process of the measurement and
the associated atomic evolution. Analytical formulas of the atomic distribution
momenta are derived in the weak coupling regime both for short and long time
behavior, and they are in good agreement with those obtained by a Monte-Carlo
simulation. The experimental implementation of the proposed heterodyne
detection scheme is discussed. The role played in the squeezing process by the
spontaneous emission is considered
Thermodynamics of Dyonic Lifshitz Black Holes
Black holes with asymptotic anisotropic scaling are conjectured to be gravity
duals of condensed matter system close to quantum critical points with
non-trivial dynamical exponent z at finite temperature. A holographic
renormalization procedure is presented that allows thermodynamic potentials to
be defined for objects with both electric and magnetic charge in such a way
that standard thermodynamic relations hold. Black holes in asymptotic Lifshitz
spacetimes can exhibit paramagnetic behavior at low temperature limit for
certain values of the critical exponent z, whereas the behavior of AdS black
holes is always diamagnetic.Comment: 26 pages, 4 figure
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