1,095 research outputs found
Bragg spectroscopic interferometer and quantum measurement-induced correlations in atomic Bose-Einstein condensates
We theoretically analyze the Bragg spectroscopic interferometer of two
spatially separated atomic Bose-Einstein condensates that was experimentally
realized by Saba et al. [Science 2005 v307 p1945] by continuously monitoring
the relative phase evolution. Even though the atoms in the light-stimulated
Bragg scattering interact with intense coherent laser beams, we show that the
phase is created by quantum measurement-induced back-action on the homodyne
photo-current of the lasers, opening possibilities for quantum-enhanced
interferometric schemes. We identify two regimes of phase evolution: a running
phase regime which was observed in the experiment of Saba et al., that is
sensitive to an energy offset and suitable for an interferometer, and a trapped
phase regime, that can be insensitive to applied forces and detrimental to
interferometric applications.Comment: 14 pages, 3 figure
Collisional excitation of doubly and triply deuterated ammonia NDH and ND by H
The availability of collisional rate coefficients is a prerequisite for an
accurate interpretation of astrophysical observations, since the observed media
often harbour densities where molecules are populated under non--LTE
conditions. In the current study, we present calculations of rate coefficients
suitable to describe the various spin isomers of multiply deuterated ammonia,
namely the NDH and ND isotopologues. These calculations are based on
the most accurate NH--H potential energy surface available, which has
been modified to describe the geometrical changes induced by the nuclear
substitutions. The dynamical calculations are performed within the
close--coupling formalism and are carried out in order to provide rate
coefficients up to a temperature of = 50K. For the various
isotopologues/symmetries, we provide rate coefficients for the energy levels
below 100 cm. Subsequently, these new rate coefficients are used
in astrophysical models aimed at reproducing the NHD, NDH and ND
observations previously reported towards the prestellar cores B1b and 16293E.
We thus update the estimates of the corresponding column densities and find a
reasonable agreement with the previous models. In particular, the
ortho--to--para ratios of NHD and NHD are found to be consistent with
the statistical ratios
Transition Delay Using Biomimetic Fish Scale Arrays
Aquatic animals have developed effective strategies to reduce their body drag over a long period of time. In this work, the influence of the scales of fish on the laminar-to-turbulent transition in the boundary layer is investigated. Arrays of biomimetic fish scales in typical overlapping arrangements are placed on a flat plate in a low-turbulence laminar water channel. Transition to turbulence is triggered by controlled excitation of a Tollmien-Schlichting (TS) wave. It was found that the TS wave can be attenuated with scales on the plate which generate streamwise streaks. As a consequence, the transition location was substantially delayed in the downstream direction by 55% with respect to the uncontrolled reference case. This corresponds to a theoretical drag reduction of about 27%. We thus hypothesize that fish scales can stabilize the laminar boundary layer and prevent it from early transition, reducing friction drag. This technique can possibly be used for bio-inspired surfaces as a laminar flow control means
Photonic spectrum of bichromatic optical lattices
We study the photonic spectrum of a one-dimensional optical lattice
possessing a double primitive cell, when the atoms are well localized at the
lattice minima. While a one-dimensional lattice with a simple Wigner-Seitz cell
always possesses a photonic bandgap at the atomic resonance, in this
configuration the photonic transmission spectrum may exhibit none, double or
multiple photonic bandgaps depending on the ratio between the interparticle
distance inside the cell and the cell size . The transmission
spectra of a weak incident probe are evaluated when the atoms are trapped in
free space and inside an optical resonator for realistic experimental
parameters.Comment: 10 pages, 10 figures, to appear in PR
NON INTRUSIVE MEASUREMENTS OF A LPP COMBUSTOR UNDER ELEVATED PRESSURE CONDITIONS
ABSTRACT To meet increasingly tight regulations on emission control appropriate combustor designs need to be developed. With different combustion concepts like RQL (Rich Quench Lean) and LPP (Lean Premixed Prevaporized) it has been proven that it is possible to reach the objective of a significant reduction of the NO X emissions. To gain further insight into the real combustion process it is of importance to be able to "look into" the flame without interfering with the actual combustion process. At the combustion laboratory of the Institute of Flight Propulsion at Munich University of Technology a combustion test facility is set up to study combustion characteristics under pressure up to 6 bar and inlet airflow temperature up to 650 K. A newly designed LPP concept was adapted into an optically accessible model combustion chamber. The objective of the study was to operate the LPP combustor under semi-realistic conditions and to obtain more knowledge on the influence of pressure on the combustion process. With suitable non-intrusive laser-spectroscopic measuring techniques like LIF (Laser Induced Fluorescence) the fuel spray, the nitric oxides and the hydroxyl radical were detected in several planes parallel to the combustor axis at different combustor pressures. As expected the pressure has a strong effect on droplet distribution and evaporation. Also with increasing pressure it was possible to operate the combustor under leaner conditions. A strong dependence on pressure of the formation of nitric oxides was detected. To quantify these results samples with a water-cooled probe were taken, analyzed and compared with the non intrusive measurements
Ultrafast preparation and strong-field ionization of an atomic Bell-like state
Molecules are many body systems with a substantial amount of entanglement
between their electrons. Is there a way to break the molecular bond of a
diatomic molecule and obtain two atoms in their ground state which are still
entangled and form a Bell-like state? We present a scheme that allows for the
preparation of such entangled atomic states from single oxygen molecules on
femtosecond time scales. The two neutral oxygen atoms are entangled in the
magnetic quantum number of their valence electrons. In a time-delayed probe
step, we employ non-adiabatic tunnel ionization, which is a magnetic quantum
number-sensitive mechanism. We then investigate correlations by comparing
single and double ionization probabilities of the Bell-like state. The
experimental results agree with the predictions for an entangled state.Comment: 20 pages, 7 figures, 1 tabl
- …