330 research outputs found
Cooperative effects on Optical Forces- Dicke's Bullet
We investigate the cooperative effects on optical forces in a system of N two
level atoms occupying a volume of dimensions to within , where
lambda is radiation wavelength and is driven by a coherent radiation field with
a spatial profile like Laguerre-Gaussian beam or ideal Bessel beam.We show a
dramatic enhancement on optical forces as well as the angular momentum imparted
to the atom by a factor of .Comment: 10 pages + 1 figure (submitted to PRL
Partially lossless compression of DICOM image sets
In this paper a new approach to the compression of DICOM image sets is presented. For this task, a specific image projection space is created by employing principal component analysis. A subset from the initial image set, which can include regions of interest, is selected and used in the projection space creation. That way, these images can be reconstructed lossless, while the residual images are reconstructed with little loss of information. As shown by conducted experiments, the proposed method yields mean absolute errors below those of linear interpolation methods, yet at the same time achieves evidently higher compression ratios than compared image compression algorithms.Sociedad Argentina de Informática e Investigación Operativ
Ultra-cold atoms in an optical cavity: two-mode laser locking to the cavity avoiding radiation pressure
The combination of ultra-cold atomic clouds with the light fields of optical
cavities provides a powerful model system for the development of new types of
laser cooling and for studying cooperative phenomena. These experiments
critically depend on the precise tuning of an incident pump laser with respect
to a cavity resonance. Here, we present a simple and reliable experimental
tuning scheme based on a two-mode laser spectrometer. The scheme uses a first
laser for probing higher-order transversal modes of the cavity having an
intensity minimum near the cavity's optical axis, where the atoms are confined
by a magnetic trap. In this way the cavity resonance is observed without
exposing the atoms to unwanted radiation pressure. A second laser, which is
phase-locked to the first one and tuned close to a fundamental cavity mode
drives the coherent atom-field dynamics.Comment: 7 pages, 7 figure
Scaling properties of cavity-enhanced atom cooling
We extend an earlier semiclassical model to describe the dissipative motion
of N atoms coupled to M modes inside a coherently driven high-finesse cavity.
The description includes momentum diffusion via spontaneous emission and cavity
decay. Simple analytical formulas for the steady-state temperature and the
cooling time for a single atom are derived and show surprisingly good agreement
with direct stochastic simulations of the semiclassical equations for N atoms
with properly scaled parameters. A thorough comparison with standard free-space
Doppler cooling is performed and yields a lower temperature and a cooling time
enhancement by a factor of M times the square of the ratio of the atom-field
coupling constant to the cavity decay rate. Finally it is shown that laser
cooling with negligible spontaneous emission should indeed be possible,
especially for relatively light particles in a strongly coupled field
configuration.Comment: 7 pages, 5 figure
Cold atoms in a high-Q ring-cavity
We report the confinement of large clouds of ultra-cold 85-Rb atoms in a
standing-wave dipole trap formed by the two counter-propagating modes of a
high-Q ring-cavity. Studying the properties of this trap we demonstrate loading
of higher-order transverse cavity modes and excite recoil-induced resonances.Comment: 4 pages, 4 figure
Raman superradiance and spin lattice of ultracold atoms in optical cavities
We investigate synthesis of a hyperfine spin lattice in an atomic
Bose-Einstein condensate, with two hyperfine spin components, inside a
one-dimensional high-finesse optical cavity, using off-resonant superradiant
Raman scattering. Spatio-temporal evolution of the relative population of the
hyperfine spin modes is examined numerically by solving the coupled
cavity-condensate mean field equations in the dispersive regime. We find,
analytically and numerically, that beyond a certain threshold of the transverse
laser pump, Raman superradiance and self-organization of the hyperfine spin
components simultaneously occur and as a result a magnetic lattice is formed.
The effects of an extra laser pump parallel to the cavity axis and the
time-dependence of the pump strength on the synthesis of a sharper lattice are
also addressed.Comment: Accepted for publication in New Journal of Physics. 16 pages and 6
figure
Cavity Assisted Nondestructive Laser Cooling of Atomic Qubits
We analyze two configurations for laser cooling of neutral atoms whose
internal states store qubits. The atoms are trapped in an optical lattice which
is placed inside a cavity. We show that the coupling of the atoms to the damped
cavity mode can provide a mechanism which leads to cooling of the motion
without destroying the quantum information.Comment: 12 page
Higher education and unemployment in Europe : an analysis of the academic subject and national effects
This paper examines the impact of an academic degree and field of study on short and long-term unemployment across Europe (EU15). Labour Force Survey (LFS) data on over half a million individuals are utilised for that purpose. The harmonized LFS classification of level of education and field of study overcomes past problems of comparability across Europe. The study analyses (i) the effect of an academic degree at a European level, (ii) the specific effect of 14 academic subjects and (iii) country specific effects. The results indicate that an academic degree is more effective on reducing the likelihood of short-term than long-term unemployment. This general pattern even though it is observed for most of the academic subjects its levels show significant variation across disciplines and countries
Hopf algebras, coproducts and symbols: an application to Higgs boson amplitudes
We show how the Hopf algebra structure of multiple polylogarithms can be used
to simplify complicated expressions for multi-loop amplitudes in perturbative
quantum field theory and we argue that, unlike the recently popularized
symbol-based approach, the coproduct incorporates information about the zeta
values. We illustrate our approach by rewriting the two-loop helicity
amplitudes for a Higgs boson plus three gluons in a simplified and compact form
involving only classical polylogarithms.Comment: 46 page
Manipulation of Cold Atomic Collisions by Cavity QED Effects
We show how the dynamics of collisions between cold atoms can be manipulated
by a modification of spontaneous emission times. This is achieved by placing
the atomic sample in a resonant optical cavity. Spontaneous emission is
enhanced by a combination of multiparticle entanglement together with a higher
density of modes of the modified vacuum field, in a situation akin to
superradiance. A specific situation is considered and we show that this effect
can be experimentally observed as a large suppression in trap-loss rates.Comment: RevTex, 2 EPS figures; scheduled for Phys. Rev. Lett. 19 Feb 01, with
minor change
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