1,462 research outputs found
Generation and Evolution of Spin Entanglement in NRQED
A complete analysis on the generation of spin entanglement from NRQED is
presented. The results of entanglement are obtained with relativistic
correction to the leading order of (v/c)^2. It is shown that to this order the
degree of entanglement of a singlet state does not change under time evolution
whereas the triplet state can change.Comment: 8 pages, 1 figure, to appear in Phys. Rev.
Sub-wavelength imaging at infrared frequencies using an array of metallic nanorods
We demonstrate that an array of metallic nanorods enables sub-wavelength
(near-field) imaging at infrared frequencies. Using an homogenization approach,
it is theoretically proved that under certain conditions the incoming radiation
can be transmitted by the array of nanorods over a significant distance with
fairly low attenuation. The propagation mechanism does not involve a resonance
of material parameters and thus the resolution is not strongly affected by
material losses and has wide bandwidth. The sub-wavelength imaging with
resolution by silver rods at 30 THz is demonstrated numerically
using full-wave electromagnetic simulator.Comment: 12 pages, 16 figures, submitted to PR
Exciton-LO-phonon dynamics in InAs/GaAs quantum dots: Effects of zone-edge phonon damping
The dynamics of an exciton-LO-phonon system after an ultrafast optical
excitation in an InAs/GaAs quantum dot is studied theoretically. Influence of
anharmonic phonon damping and its interplay with the phonon dispersion is
analyzed. The signatures of the zone-edge decay process in the absorption
spectrum and time evolution are highlighted, providing a possible way of
experimental investigation on phonon anharmonicity effects.Comment: 10 pages, 2 figure
Analytical model for laser-assisted recombination of hydrogenic atoms
We introduce a new method that allows one to obtain an analytical cross
section for the laser-assisted electron-ion collision in a closed form. As an
example we perform a calculation for the hydrogen laser-assisted recombination.
The -matrix element for the process is constructed from an exact electron
Coulomb-Volkov wave function and an approximate laser modified hydrogen state.
An explicit expression for the field-enhancement coefficient of the process is
expressed in terms of the dimensionless parameter , where and are the electron charge
and momentum respectively, and and are the
amplitude and frequency of the laser field respectively. The simplified version
of the cross section of the process is derived and analyzed within a soft
photon approximation.Comment: 10 page
A rotating cavity for high-field angle-dependent microwave spectroscopy of low-dimensional conductors and magnets
The cavity perturbation technique is an extremely powerful method for
measuring the electrodynamic response of a material in the millimeter- and
sub-millimeter spectral range (10 GHz to 1 THz), particularly in the case of
high-field/frequency magnetic resonance spectroscopy. However, the application
of such techniques within the limited space of a high-field magnet presents
significant technical challenges. We describe a 7.62 mm x 7.62 mm (diameter x
length) rotating cylindrical cavity which overcomes these problems.Comment: 11 pages including 8 figure
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Materials for phantoms for terahertz pulsed imaging
Phantoms are commonly used in medical imaging for quality assurance, calibration, research and teaching. They may include test patterns or simulations of organs, but in either case a tissue substitute medium is an important component of the phantom. The aim of this work was to identify materials suitable for use as tissue substitutes for the relatively new medical imaging modality terahertz pulsed imaging. Samples of different concentrations of the candidate materials TX151 and napthol green dye were prepared, and measurements made of the frequency-dependent absorption coefficient (0.5 to 1.5 THz) and refractive index (0.5 to 1.0 THz). These results were compared qualitatively with measurements made in a similar way on samples of excised human tissue (skin, adipose tissue and striated muscle). Both materials would be suitable for phantoms where the dominant mechanism to be simulated is absorption (similar to ∼100 cm(-1) at 1 THz) and where simulation of the strength of reflections from boundaries is not important; for example, test patterns for spatial resolution measurements. Only TX151 had a frequency-dependent refractive index close to that of tissue, and could therefore be used to simulate the layered structure of skin, the complexity of microvasculature or to investigate frequency-dependent interference effects that have been noted in terahertz images
Terahertz Magneto Optical Polarization Modulation Spectroscopy
We report the development of new terahertz techniques for rapidly measuring
the complex Faraday angle in systems with broken time-reversal symmetry using
the cyclotron resonance of a GaAs two-dimensional electron gas in a magnetic
field as a system for demonstration of performance. We have made polarization
modulation, high sensitivity (< 1 mrad) narrow band rotation measurements with
a CW optically pumped molecular gas laser, and by combining the distinct
advantages of terahertz (THz) time domain spectroscopy and polarization
modulation techniques, we have demonstrated rapid broadband rotation
measurements to < 5 mrad precision.Comment: 25 pages including 7 figures, introduces use of rotating polarizer
with THz TDS for Complex Faraday Angle determinatio
A constraint on antigravity of antimatter from precision spectroscopy of simple atoms
Consideration of antigravity for antiparticles is an attractive target for
various experimental projects. There are a number of theoretical arguments
against it but it is not quite clear what kind of experimental data and
theoretical suggestions are involved. In this paper we present straightforward
arguments against a possibility of antigravity based on a few simple
theoretical suggestions and some experimental data. The data are: astrophysical
data on rotation of the Solar System in respect to the center of our galaxy and
precision spectroscopy data on hydrogen and positronium. The theoretical
suggestions for the case of absence of the gravitational field are: equality of
electron and positron mass and equality of proton and positron charge. We also
assume that QED is correct at the level of accuracy where it is clearly
confirmed experimentally
Properties of metastable alkaline-earth-metal atoms calculated using an accurate effective core potential
The first three electronically excited states in the alkaline-earth-metal
atoms magnesium, calcium, and strontium comprise the (nsnp) triplet P^o_J
(J=0,1,2) fine-structure manifold. All three states are metastable and are of
interest for optical atomic clocks as well as for cold-collision physics. An
efficient technique--based on a physically motivated potential that models the
presence of the ionic core--is employed to solve the Schroedinger equation for
the two-electron valence shell. In this way, radiative lifetimes, laser-induced
clock shifts, and long-range interaction parameters are calculated for
metastable Mg, Ca, and Sr.Comment: 13 pages, 9 table
Metallic Carbon Nanotube Quantum Dots with Broken Symmetries as a Platform for Tunable Terahertz Detection
Quantum dots (QD) in metallic single-walled carbon nanotubes (SWNT) have
shown great potential to build sensitive terahertz (THz) detection devices
usually based on photon-assisted tunneling. A recently reported mechanism based
on a combination of resonant QD transitions and asymmetries in the tunneling
barriers results in narrow linewidth photocurrent response with a large signal
to noise ratio under weak THz radiation. However in such devices, due to
metallic SWNTs linear dispersion relation, the detection range is intrinsically
limited to allowed energy transitions between equidistant quantized states set
by the QD length. Here, we show that simultaneously breaking translational,
rotational and mirror symmetries in metallic SWNT QDs leads to a quantized
spectrum with non-equidistant energy levels. This result stems from
tight-binding and first-principle simulations of a defect-induced metallic
zigzag SWNT QD and is validated experimentally by scanning tunneling
spectroscopy studies. Importantly, we show that breaking symmetries in metallic
SWNT QDs of arbitrary chirality strongly relaxes the selection rules in the
electric dipole approximation, leading to a richer set of allowed optical
transitions spanning frequencies from as low as 1 THz up to several tens of THz
for a 10 nm QD. Such findings make metallic carbon nanotube QDs with
broken symmetries a promising platform to design tunable THz detectors
operating above liquid helium temperatures. In this context, we propose a
device design based on a metallic SWNT QD engineered with artificially created
defects.Comment: 20 pages, 15 figure
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