3,318 research outputs found
Summary of past experience in natural laminar flow and experimental program for resilient leading edge
The potential of natural laminar flow for significant drag reduction and improved efficiency for aircraft is assessed. Past experience with natural laminar flow as reported in published and unpublished data and personal observations of various researchers is summarized. Aspects discussed include surface contour, waviness, and smoothness requirements; noise and vibration effects on boundary layer transition, boundary layer stability criteria; flight experience with natural laminar flow and suction stabilized boundary layers; and propeller slipstream, rain, frost, ice and insect contamination effects on boundary layer transition. The resilient leading edge appears to be a very promising method to prevent leading edge insect contamination
Proposed realization of the Dicke-model quantum phase transition in an optical cavity QED system
The Dicke model describing an ensemble of two-state atoms interacting with a single quantized mode of the electromagnetic field (with omission of the Â^2 term) exhibits a zero-temperature phase transition at a critical value of the dipole coupling strength. We propose a scheme based on multilevel atoms and cavity-mediated Raman transitions to realize an effective Dicke model operating in the phase transition regime. Optical light from the cavity carries signatures of the critical behavior, which is analyzed for the thermodynamic limit where the number of atoms is very large
Low Reynolds number airfoil survey, volume 1
The differences in flow behavior two dimensional airfoils in the critical chordlength Reynolds number compared with lower and higher Reynolds number are discussed. The large laminar separation bubble is discussed in view of its important influence on critical Reynolds number airfoil behavior. The shortcomings of application of theoretical boundary layer computations which are successful at higher Reynolds numbers to the critical regime are discussed. The large variation in experimental aerodynamic characteristic measurement due to small changes in ambient turbulence, vibration, and sound level is illustrated. The difficulties in obtaining accurate detailed measurements in free flight and dramatic performance improvements at critical Reynolds number, achieved with various types of boundary layer tripping devices are discussed
Initial state preparation with dynamically generated system-environment correlations
The dependence of the dynamics of open quantum systems upon initial
correlations between the system and environment is an utterly important yet
poorly understood subject. For technical convenience most prior studies assume
factorizable initial states where the system and its environments are
uncorrelated, but these conditions are not very realistic and give rise to
peculiar behaviors. One distinct feature is the rapid build up or a sudden jolt
of physical quantities immediately after the system is brought in contact with
its environments. The ultimate cause of this is an initial imbalance between
system-environment correlations and coupling. In this note we demonstrate
explicitly how to avoid these unphysical behaviors by proper adjustments of
correlations and/or the coupling, for setups of both theoretical and
experimental interest. We provide simple analytical results in terms of
quantities that appear in linear (as opposed to affine) master equations
derived for factorized initial states.Comment: 6 pages, 2 figure
Non-classical photon pair generation in atomic vapours
A scheme for the generation of non-classical pairs of photons in atomic
vapours is proposed. The scheme exploits the fact that the cross correlation of
the emission of photons from the extreme transitions of a four-level cascade
system shows anti-bunching which has not been reported earlier and which is
unlike the case of the three level cascade emission which shows bunching. The
Cauchy-Schwarz inequality which is the ratio of cross-correlation to the auto
correlation function in this case is estimated to be for
controllable time delay, and is one to four orders of magnitude larger compared
to previous experiments. The choice of Doppler free geometry in addition to the
fact that at three photon resonance the excitation/deexcitation processes occur
in a very narrow frequency band, ensures cleaner signals.Comment: 18 pages, 7 figure
Quantum coherence of discrete kink solitons in ion traps
We propose to realize quantized discrete kinks with cold trapped ions. We
show that long-lived solitonlike configurations are manifested as deformations
of the zigzag structure in the linear Paul trap, and are topologically
protected in a circular trap with an odd number of ions. We study the
quantum-mechanical time evolution of a high-frequency, gap separated internal
mode of a static kink and find long coherence times when the system is cooled
to the Doppler limit. The spectral properties of the internal modes make them
ideally suited for manipulation using current technology. This suggests that
ion traps can be used to test quantum-mechanical effects with solitons and
explore ideas for the utilization of the solitonic internal-modes as carriers
of quantum information.Comment: 5 pages, 4 figures ; minor correction
Vacuum fluctuations and the conditional homodyne detection of squeezed light
Conditional homodyne detection of quadrature squeezing is compared with
standard nonconditional detection. Whereas the latter identifies
nonclassicality in a quantitative way, as a reduction of the noise power below
the shot noise level, conditional detection makes a qualitative distinction
between vacuum state squeezing and squeezed classical noise. Implications of
this comparison for the realistic interpretation of vacuum fluctuations
(stochastic electrodynamics) are discussed.Comment: 14 pages, 7 figures, to appear in J. Opt. B: Quantum Semiclass. Op
Observation of ground-state quantum beats in atomic spontaneous emission
We report ground-state quantum beats in spontaneous emission from a
continuously driven atomic ensemble. Beats are visible only in an intensity
autocorrelation and evidence spontaneously generated coherence in radiative
decay. Our measurement realizes a quantum eraser where a first photon detection
prepares a superposition and a second erases the "which-path" information in
the intermediate state.Comment: 4 pages, 4 figures, to appear in Phys. Rev. Letter
Decoherence at constant excitation
We present a simple exactly solvable extension of of the Jaynes-Cummings
model by adding dissipation. This is done such that the total number of
excitations is conserved. The Liouville operator in the resulting master
equation can be reduced to blocks of matrices
Single Atom Detection With Optical Cavities
We present a thorough analysis of single atom detection using optical
cavities. The large set of parameters that influence the signal-to-noise ratio
for cavity detection is considered, with an emphasis on detunings, probe power,
cavity finesse and photon detection schemes. Real device operating restrictions
for single photon counting modules and standard photodiodes are included in our
discussion, with heterodyne detection emerging as the clearly favourable
technique, particularly for detuned detection at high power.Comment: 11 pages, 8 figures, submitted to PRA, minor changes in Secs. I and
IVD.2, and revised Fig.
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