2,822 research outputs found
A Single Atom as a Mirror of an Optical Cavity
By tightly focussing a laser field onto a single cold ion trapped in front of
a far-distant dielectric mirror, we could observe a quantum electrodynamic
effect whereby the ion behaves as the optical mirror of a Fabry-P\'erot cavity.
We show that the amplitude of the laser field is significantly altered due to a
modification of the electromagnetic mode structure around the atom in a novel
regime in which the laser intensity is already changed by the atom alone. e
propose a direct application of this system as a quantum memory for single
photons.Comment: 7 pages, 3 figures, to appear in Physical Review Letter
Symmetry energy and neutron-proton radii studies with a Wigner-Heisenberg monopole-monopole interaction
The symmetry energy in nuclei is studied using a monopole-monopole two boby
interaction which has an isospin dependent term. A Hartree theory is developed
for this interaction which has an oscillator shell model basis with
corresponding shell structure. The role of shell structure on the symmetry
energy is then studied. We also find that the strength of the Heisenberg
interaction is very important for understanding the difference between proton
and neutron radii and features associated with halo nuclei.
PACS numbers: 21.10.Sf, 21.65Cd, 21.65EfComment: 1 table, i figur
QED with a spherical mirror
We investigate the Quantum-Electro-Dynamic properties of an atomic electron
close to the focus of a spherical mirror. We first show that the spontaneous
emission and excited state level shift of the atom can be fully suppressed with
mirror-atom distances of many wavelengths. A three-dimensional theory predicts
that the spectral density of vacuum fluctuations can indeed vanish within a
volume around the atom, with the use of a far distant mirror
covering only half of the atomic emission solid angle. The modification of
these QED atomic properties is also computed as a function of the mirror size
and large effects are found for only moderate numerical apertures. We also
evaluate the long distance ground state energy shift (Casimir-Polder shift) and
find that it scales as at the focus of a hemi-spherical mirror
of radius , as opposed to the well known scaling law for an
atom at a distance from an infinite plane mirror. Our results are relevant
for investigations of QED effects, and also free space coupling to single atoms
using high-numerical aperture lenses.Comment: 12 pages, 4 figure
Centaur Propellant Thermal Conditioning Study
A wicking investigation revealed that passive thermal conditioning was feasible and provided considerable weight advantage over active systems using throttled vent fluid in a Centaur D-1s launch vehicle. Experimental wicking correlations were obtained using empirical revisions to the analytical flow model. Thermal subcoolers were evaluated parametrically as a function of tank pressure and NPSP. Results showed that the RL10 category I engine was the best candidate for boost pump replacement and the option showing the lowest weight penalty employed passively cooled acquisition devices, thermal subcoolers, dry ducts between burns and pumping of subcooler coolant back into the tank. A mixing correlation was identified for sizing the thermodynamic vent system mixer. Worst case mixing requirements were determined by surveying Centaur D-1T, D-1S, IUS, and space tug vehicles. Vent system sizing was based upon worst case requirements. Thermodynamic vent system/mixer weights were determined for each vehicle
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
Identification of clusters of companies in stock indices via Potts super-paramagnetic transitions
The clustering of companies within a specific stock market index is studied
by means of super-paramagnetic transitions of an appropriate q-state Potts
model where the spins correspond to companies and the interactions are
functions of the correlation coefficients determined from the time dependence
of the companies' individual stock prices. The method is a generalization of
the clustering algorithm by Domany et. al. to the case of anti-ferromagnetic
interactions corresponding to anti-correlations. For the Dow Jones Industrial
Average where no anti-correlations were observed in the investigated time
period, the previous results obtained by different tools were well reproduced.
For the Standard & Poor's 500, where anti-correlations occur, repulsion between
stocks modify the cluster structure.Comment: 4 pages; changed conten
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
Generation of entangled photons by trapped ions in microcavities under a magnetic field gradient
We propose a potential scheme to generate entangled photons by manipulating
trapped ions embedded in two-mode microcavities, respectively, assisted by a
magnetic field gradient. By means of the spin-spin coupling due to the magnetic
field gradient and the Coulomb repulsion between the ions, we show how to
efficiently generate entangled photons by detecting the internal states of the
trapped ions. We emphasize that our scheme is advantageous to create complete
sets of entangled multi-photon states. The requirement and the experimental
feasibility of our proposal are discussed in detail.Comment: 2 Tables, 2 Figures, To appear in Phys. Rev.
Experimental Setup for the Measurement of the Thermoelectric Power in Zero and Applied Magnetic Field
An experimental setup was developed for the measurement of the thermoelectric
power (TEP, Seebeck coefficient) in the temperature range from 2 to 350 K and
magnetic fields up to 140 kOe. The system was built to fit in a commercial
cryostat and is versatile, accurate and automated; using two heaters and two
thermometers increases the accuracy of the TEP measurement. High density data
of temperature sweeps from 2 to 350 K can be acquired in under 16 hours and
high density data of isothermal field sweeps from 0 to 140 kOe can be obtained
in under 2 hours. Calibrations for the system have been performed on a platinum
wire and BiSrCaCuO high superconductors.
The measured TEP of phosphor-bronze (voltage lead wire) turns to be very small,
where the absolute TEP value of phosphor-bronze wire is much less than 0.5
V/K below 80 K. For copper and platinum wires measured against to the
phosphor-bronze wire, the agreement between measured results and the literature
data is good. To demonstrate the applied magnetic field response of the system,
we report measurements of the TEP on single crystal samples of LaAgSb and
CeAgSb in fields up to 140 kOe.Comment: 10 pages, 8 figures. accepted in Measurement Science and Technolog
Measurement of the hyperfine structure of the S1/2-D5/2 transition in 43Ca+
The hyperfine structure of the S1/2-D5/2 quadrupole transition at 729 nm in
43Ca+ has been investigated by laser spectroscopy using a single trapped 43Ca+
ion. We determine the hyperfine structure constants of the metastable level as
A=-3.8931(2) MHz and B=-4.241(4) MHz. The isotope shift of the transition with
respect to 40Ca+ was measured to be 4134.713(5) MHz. We demonstrate the
existence of transitions that become independent of the first-order Zeeman
shift at non-zero low magnetic fields. These transitions might be better suited
for building a frequency standard than the well-known 'clock transitions'
between m=0 levels at zero magnetic field.Comment: corrected for sign errors in the hyperfine constants. No corrections
to were made to the data analysi
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