2,490 research outputs found
Electromagnetically Induced Transparency from a Single Atom in Free Space
We report an absorption spectroscopy experiment and the observation of
electromagnetically induced transparency from a single trapped atom. We focus a
weak and narrowband Gaussian light beam onto an optically cooled Barium ion
using a high numerical aperture lens. Extinction of this beam is observed with
measured values of up to 1.3 %. We demonstrate electromagnetically induced
transparency of the ion by tuning a strong control beam over a two-photon
resonance in a three-level lambda-type system. The probe beam extinction is
inhibited by more than 75 % due to population trapping.Comment: 4 pages, 3 figure
Experimental proposal for accurate determination of the phase relaxation time and testing a formation of thermalized non-equilibrated matter in highly excited quantum many-body systems
We estimate how accurate the phase relaxation time of quantum many-body
systems can be determined from data on forward peaking of evaporating protons
from a compound nucleus. The angular range and accuracy of the data needed for
a reliable determination of the phase relaxation time are evaluated. The
general method is applied to analyze the inelastic scattering of 18 MeV protons
from Pt for which previously measured double differential cross sections for
two angles in the evaporating domain of the spectra show a strong forward
peaking. A new experiment for an improved determination of the phase relaxation
time is proposed. The experiment is also highly desirable for an accurate test
of a formation of thermalized non-equilibrated matter in quantum many-body
systems.Comment: 5 pages, 3 figure
Notes on Succession in Old Fields in Southeastern Ontario: the Herbs
Vegetation in abandoned hayfields was monitored during 1976-1998. An earlier successional stage followed ploughing. Changes in tree, shrub and vine populations have been reported earlier and showed expected increases in species richness and cover. Highest species richness of herbs occurred three years after ploughing. Non-woody species richness trended irregularly downward, while non-woody cover was variable, peaking in 1987. Within the herbaceous community, year-to-year changes in cover and frequency of species in the following selected groups are reported here: 18 grasses including sown and adventive species; 13 legumes including two sown species; 14 macroforbs of the Compositae, including a goldenrod, Solidago canadensis, which dominated parts of the fields; a rosette weed, Taraxacum officinalis; sedges, horsetails and some other minor components. Grasses and goldenrods were grazed, sometimes intensively and repeatedly, by insects; grasses were impacted by skipper larvae (Thymelicus lineola), and goldenrods by beetle larvae (Trirhabda spp.). Effects of repeated outbreaks on host plant cover are shown for two plots (100 m2) matching the scale of outbreaks
Spin-based quantum gating with semiconductor quantum dots by bichromatic radiation method
A potential scheme is proposed for realizing a two-qubit quantum gate in
semiconductor quantum dots. Information is encoded in the spin degrees of
freedom of one excess conduction electron of each quantum dot. We propose to
use two lasers, radiation two neighboring QDs, and tuned to blue detuning with
respect to the resonant frequencies of individual excitons. The two-qubit phase
gate can be achieved by means of both Pauli-blocking effect and dipole-dipole
coupling between intermediate excitonic states.Comment: Europhysics Letters 66 (2004) 1
Interferometric thermometry of a single sub-Doppler cooled atom
Efficient self-interference of single-photons emitted by a sideband-cooled
Barium ion is demonstrated. First, the technical tools for performing efficient
coupling to the quadrupolar transition of a single Ba ion are
presented. We show efficient Rabi oscillations of the internal state of the ion
using a highly stabilized 1.76 fiber laser resonant with the
S-D transition. We then show sideband cooling of the ion's
motional modes and use it as a means to enhance the interference contrast of
the ion with its mirror-image to up to 90%. Last, we measure the dependence of
the self-interference contrast on the mean phonon number, thereby demonstrating
the potential of the set-up for single-atom thermometry close to the motional
ground state.Comment: 6 pages, 6 figure
Nonequilibrium Response from the dissipative Liouville Equation
The problem of response of nonequilibrium systems is currently under intense
investigation. We propose a general method of solution of the Liouville
Equation for thermostatted particle systems subjected to external forces which
retains only the slow degrees of freedom, by projecting out the majority of
fast variables. Response formulae, extending the Green-Kubo relations to
dissipative dynamics are provided, and comparison with numerical data is
presented
Systematic study of Optical Feshbach Resonances in an ideal gas
Using a narrow intercombination line in alkaline earth atoms to mitigate
large inelastic losses, we explore the Optical Feshbach Resonance (OFR) effect
in an ultracold gas of bosonic Sr. A systematic measurement of three
resonances allows precise determinations of the OFR strength and scaling law,
in agreement with coupled-channels theory. Resonant enhancement of the complex
scattering length leads to thermalization mediated by elastic and inelastic
collisions in an otherwise ideal gas. OFR could be used to control atomic
interactions with high spatial and temporal resolution.Comment: Significant changes to text and figure presentation to improve
clarity. Extended supplementary material. 4 pages, 4 figures; includes
supplementary material 8 pages, 4 figures. Submitted to Physical Review
Letter
Diquark Bose-Einstein condensation
Bose-Einstein condensation (BEC) of composite diquarks in quark matter (the
color superconductor phase) is discussed using the quasi-chemical equilibrium
theory at a relatively low density region near the deconfinement phase
transition, where dynamical quark-pair fluctuations are assumed to be described
as bosonic degrees of freedom (diquarks). A general formulation is given for
the diquark formation and particle-antiparticle pair-creation processes in the
relativistic flamework, and some interesting properties are shown, which are
characteristic for the relativistic many-body system. Behaviors of transition
temperature and phase diagram of the quark-diquark matter are generally
presented in model parameter space, and their asymptotic behaviors are also
discussed. As an application to the color superconductivity, the transition
temperatures and the quark and diquark density profiles are calculated in case
with constituent/current quarks, where the diquark is in bound/resonant state.
We obtained MeV for constituent quarks and MeV
for current quarks at a moderate density (). The method
is also developed to include interdiquark interactions into the quasi-chemical
equilibrium theory within a mean-field approximation, and it is found that a
possible repulsive diquark-diquark interaction lowers the transition
temperature by nearly 50%.Comment: 21 pages, 23 figure
- …