6,399 research outputs found
Probe spectroscopy in an operating magneto-optical trap: the role of Raman transitions between discrete and continuum atomic states
We report on cw measurements of probe beam absorption and four-wave-mixing
spectra in a Rb magneto-optical trap taken while the trap is in
operation. The trapping beams are used as pump light. We concentrate on the
central feature of the spectra at small pump-probe detuning and attribute its
narrow resonant structures to the superposition of Raman transitions between
light-shifted sublevels of the ground atomic state and to atomic recoil
processes. These two contributions have different dependencies on trap
parameters and we show that the former is inhomogeneously broadened. The strong
dependence of the spectra on the probe-beam polarization indicates the
existence of large optical anisotropy of the cold-atom sample, which is
attributed to the recoil effects. We point out that the recoil-induced
resonances can be isolated from other contributions, making pump-probe
spectroscopy a highly sensitive diagnostic tool for atoms in a working MOT.Comment: 9 pages, 8 figure
Relations Among Correlation Functions in the High Temperature Phase of QCD with Broken SU(3)
Group-theoretic arguments are used to determine the dependence of two-point
correlators of quark bilinears on the current quark masses. The leading
difference between and correlators is found to be of order
times a U(1)-violating correlator. These general
arguments are consistent with Schaefer's observation that if
U(1) violation persists to high enough temperatures
then the strange can be lighter than the non-strange one.Comment: 8 page
Detail-oriented cognitive style and social communicative deficits, within and beyond the autism spectrum: independent traits that grow into developmental interdependence
At the heart of debates over underlying causes of autism is the "Kanner hypothesis" that autistic deficits in social reciprocity, and a cognitive/perceptual 'style' favouring detail-oriented cognition, co-vary in autistic individuals. A separate line of work indicates these two domains are normally distributed throughout the population, with autism representing an extremity. This realisation brings the Kanner debate into the realm of normative co-variation, providing more ways to test the hypothesis, and insights into typical development; for instance, in the context of normative functioning, the Kanner hypothesis implies social costs to spatial/numerical prowess
Train of high-power femtosecond pulses: Probe wave in a gas of prepared atoms
We present a new method for generating a regular train of ultrashort optical
pulses in a prepared two-level medium. The train develops from incident
monochromatic probe radiation travelling in a medium of atoms, which are in a
quantum mechanical superposition of dressed internal states. In the frame of
used linear theory for the probe radiation, the energy of individual pulses is
an exponentially growing function of atom density and of interaction cross
section. Pulse repetition rate is determined by the generalized Rabi frequency
and can be around 1 THz and greater. We also show that the terms, extra to the
dipole approximation, endow the gas by a new property: non-saturating
dependence of refractive index on the dressing monochromatic field intensity.
Contribution of these nonsaturating terms can be compatible with the main
dipole approximation in the wavelength region of about ten micrometers (the
range of CO_2 laser) or larger
Nondegenerate parametric down conversion in coherently prepared two-level atomic gas
We describe parametric down conversion process in a two-level atomic gas,
where the atoms are in a superposition state of relevant energy levels. This
superposition results in splitting of the phase matching condition into three
different conditions. Another, more important, peculiarity of the system under
discussion is the nonsaturability of amplification coefficients with increasing
pump wave intensity, under "sideband" generation conditions
Entanglement: Quantum or Classical?
From its seemingly non-intuitive and puzzling nature, most evident in
numerous EPR-like gedankenexperiments to its almost ubiquitous presence in
quantum technologies, entanglement is at the heart of modern quantum physics.
First introduced by Erwin Schr\"{o}dinger nearly a century ago, entanglement
has remained one of the most fascinating ideas that came out of quantum
mechanics. Here, we attempt to explain what makes entanglement fundamentally
different from any classical phenomenon. To this end, we start with a
historical overview of entanglement and discuss several hidden variables models
that were conceived to provide a classical explanation and demystify quantum
entanglement. We discuss some inequalities and bounds that are violated by
quantum states thereby falsifying the existence of some of the classical hidden
variables theories. We also discuss some exciting manifestations of
entanglement, such as N00N states and the non-separable single particle states.
We conclude by discussing some contemporary results regarding quantum
correlations and present a future outlook for the research of quantum
entanglement
Diagrammatic approach to coherent backscattering of laser light by cold atoms: Double scattering revisited
We present a diagrammatic derivation of the coherent backscattering spectrum
from two two-level atoms using the pump-probe approach, wherein the multiple
scattering signal is deduced from single-atom responses, and provide a physical
interpretation of the single-atom building blocks.Comment: 16 pages, 7 figure
Resonant excitonic emission of a single quantum dot in the Rabi regime
We report on coherent resonant emission of the fundamental exciton state in a
single semiconductor GaAs quantum dot. Resonant regime with picoseconde laser
excitation is realized by embedding the quantum dots in a waveguiding
structure. As the pulse intensity is increased, Rabi oscillation is observed up
to three periods. The Rabi regime is achieved owing to an enhanced light-matter
coupling in the waveguide. This is due to a \emph{slow light effect}
(), occuring when an intense resonant pulse propagates in a
medium. The resonant control of the quantum dot fundamental transition opens
new possibilities in quantum state manipulation and quantum optics experiments
in condensed matter physics.Comment: Submitted to Phys. Rev. Let
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