31,138 research outputs found
Optomechanical position detection enhanced by de-amplification using intracavity squeezing
It has been predicted and experimentally demonstrated that by injecting
squeezed light into an optomechanical device it is possible to enhance the
precision of a position measurement. Here, we present a fundamentally different
approach where the squeezing is created directly inside the cavity by a
nonlinear medium. Counterintuitively, the enhancement of the signal to noise
ratio works by de-amplifying precisely the quadrature that is sensitive to the
mechanical motion without losing quantum information. This enhancement works
for systems with a weak optomechanical coupling and/or strong mechanical
damping. This could allow for larger mechanical bandwidth of quantum limited
detectors based on optomechanical devices. Our approach can be
straightforwardly extended to Quantum Non Demolition (QND) qubit detection.Comment: references added, slight change
Enhanced binding revisited for a spinless particle in non-relativistic QED
We consider a spinless particle coupled to a quantized Bose field and show
that such a system has a ground state for two classes of short-range potentials
which are alone too weak to have a zero-energy resonance
Chiral phase transitions in strong chromomagnetic fields at finite temperature and dimensional reduction
Dynamical fermion mass generation in external chromomagnetic fields is
considered at non--zero temperature. The general features of dynamical chiral
symmetry breaking () are investigated for several field
configurations in relation to their symmetry properties and the form of the
quark spectrum. According to the fields, there arises dimensional reduction by
one or two units. In all cases there exists even at weak quark
attraction, confirming the idea about the dimensional insensitivity of this
mechanism in a chromomagnetic field.Comment: LATEX file, 12 pages, no figure
Spin-phonon coupling in antiferromagnetic chromium spinels
The temperature dependence of eigenfrequencies and intensities of the IR
active modes has been investigated for the antiferromagnetic chromium spinel
compounds CdCr2O4, ZnCr2O4, ZnCr2S4, ZnCr2Se4, and HgCr2S4 by IR spectroscopy
for temperatures from 5 K to 300 K. At the transition into the magnetically
ordered phases, and driven by spin-phonon coupling, most compounds reveal
significant splittings of the phonon modes. This is true for geometrically
frustrated CdCr2O4, and ZnCr2O4, for bond frustrated ZnCr2S4 and for ZnCr2Se4,
which also is bond frustrated, but dominated by ferromagnetic exchange. The
pattern of splitting is different for the different compounds and crucially
depends on the nature of frustration and of the resulting spin order. HgCr2S4,
which is almost ferromagnetic, exhibits no splitting of the eigenfrequencies,
but shows significant shifts due to ferromagnetic spin fluctuations.Comment: 15 pages, 6 figure
Optical phonons, spin correlations, and spin-phonon coupling in the frustrated pyrochlore magnets CdCr2O4 and ZnCr2O4
We report on infrared, Raman, magnetic susceptibility, and specific heat
measurements on CdCr2O4 and ZnCr2O4 single crystals. We estimate the
nearest-neighbor and next-nearest neighbor exchange constants from the magnetic
susceptibility and extract the spin-spin correlation functions obtained from
the magnetic susceptibility and the magnetic contribution to the specific heat.
By comparing with the frequency shift of the infrared optical phonons above TN
, we derive estimates for the spin-phonon coupling constants in these systems.
The observation of phonon modes which are both Raman and infrared active
suggest the loss of inversion symmetry below the Neel temperature in CdCr2O4 in
agreement with theoretical predictions by Chern and coworkers [Phys. Rev. B 74,
060405 (2006)]. In ZnCr2O4 several new modes appear below TN, but no phonon
modes could be detected which are both Raman and infrared active indicating the
conservation of inversion symmetry in the low temperature phase.Comment: 11 pages, 13 figure
Enhancement of ferromagnetism by nickel doping in the 112 cobaltite EuBaCo2O5.50
The study of the ordered oxygen deficient perovskite EuBaCo2-xNixO5.50 shows
that the doping of cobalt sites by nickel induces a strong ferromagnetic
component at low temperature in the antiferromagnetic matrix of EuBaCo2O5.50.
This system exhibits indeed phase separation, i.e. consists of ferromagnetic
domains embedded in the antiferromagnetic matrix of EuBaCo2O5.50. Besides, a
magnetic transition is observed for the first time at 40K in the undoped and
nickel doped phases, which can be attributed to the ferromagnetic ordering of
the Eu3+ moments below this temperature. Moreover sharp ultra magnetization
multisteps are observed below 5K, characteristic of motion of domain walls in a
strong pinning system and very different from any metamagnetic transition
Multilayer gas cells for sub-Doppler spectroscopy
We have carried out theoretical research on ultra-high resolution
spectroscopy of atoms (or molecules) in the suggested cell with a series of
plane-parallel thin gas layers between spatially separated gas regions of this
cell for optical pumping and probing. It is shown the effective velocity
selection of optically pumped atoms because of their specific transit time and
collisional relaxation in such a cell, which lead to narrow sub-Doppler
resonances in absorption of the probe monochromatic light beam. Resolution of
this spectroscopic method is analyzed in cases of stationary and definite
nonstationary optical pumping of atoms by the broadband radiation versus
geometrical parameters of given cells and pumping intensity. The suggested
multilayer gas cell is the compact analog of many parallel atomic (molecular)
beams and may be used also as the basis of new compact optical frequency
standards of high accuracy.Comment: 12 pages, 4 figure
Open Access to Scientific Results and Data. European Union's Efforts through Openaire and Openaireplus FP7 Projects: Cypriot Participation
The paper presents the introduction of Open Access movement in the Academic environment, pros and cons of the adoption of OA by Universities and how the European Union is enforcing the use of Open Access. The ways of implementing OA, the policies of publishers and journals regarding the deposits of publications and the RoMEO and Juliet projects are also referred in an effort to give an overview of the conditions in exploiting Open Access, either as authors, publishers or end users. The adoption of the Berlin declaration on Open Access to Knowledge in the Sciences and Humanities by the Senate of the University of Cyprus is commented in the paper. Furthermore an analysis of the projects OpenAIRE and OpenAIREplus in which the University of Cyprus Library is involved is provided.University of Cyprus Library, 75 Kallipoleos Str. P. O. Box 20537 1678 Nicosia, Cyprus
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