23,966 research outputs found
Linear-optical processing cannot increase photon efficiency
We answer the question whether linear-optical processing of the states
produced by one or multiple imperfect single-photon sources can improve the
single-photon fidelity. This processing can include arbitrary interferometers,
coherent states, feedforward, and conditioning on results of detections. We
show that without introducing multiphoton components, the single-photon
fraction in any of the single-mode states resulting from such processing cannot
be made to exceed the efficiency of the best available photon source. If
multiphoton components are allowed, the single-photon fidelity cannot be
increased beyond 1/2. We propose a natural general definition of the
quantum-optical state efficiency, and show that it cannot increase under
linear-optical processing.Comment: 4 pages, 3 figure
Analysis of longitudinal pilot-induced oscillation tendencies of YF-12 aircraft
Aircraft flight and ground tests and simulator studies were conducted to explore pilot-induced oscillation tendencies. Linear and nonlinear calculations of the integrated flight control system's characteristics were made to analyze and predict the system's performance and stability. The investigations showed that the small-amplitude PIO tendency was caused by the interaction of the pilot with a combination of the aircraft's short-period poles and the structural first bending mode zeros. It was found that the large-amplitude PIO's were triggered by abrupt corrective control actions by the pilot, which caused the stability augmentation system servo to position and rate limit. The saturation in turn caused additional phase lag, further increasing the tendency of the overall system to sustain a PIO
Nanoscale magnetometry using a single spin system in diamond
We propose a protocol to estimate magnetic fields using a single
nitrogen-vacancy (N-V) center in diamond, where the estimate precision scales
inversely with time, ~1/T$, rather than the square-root of time. The method is
based on converting the task of magnetometry into phase estimation, performing
quantum phase estimation on a single N-V nuclear spin using either adaptive or
nonadaptive feedback control, and the recently demonstrated capability to
perform single-shot readout within the N-V [P. Neumann et. al., Science 329,
542 (2010)]. We present numerical simulations to show that our method provides
an estimate whose precision scales close to ~1/T (T is the total estimation
time), and moreover will give an unambiguous estimate of the static magnetic
field experienced by the N-V. By combining this protocol with recent proposals
for scanning magnetometry using an N-V, our protocol will provide a significant
decrease in signal acquisition time while providing an unambiguous spatial map
of the magnetic field.Comment: 8 pages and 5 figure
Equivalence between two-mode spin squeezed states and pure entangled states with equal spin
We prove that a pure entangled state of two subsystems with equal spin is
equivalent to a two-mode spin-squeezed state under local operations except for
a set of bipartite states with measure zero, and we provide a counterexample to
the generalization of this result to two subsystems of unequal spin.Comment: 6 pages, no figure
Adaptive Quantum Measurements of a Continuously Varying Phase
We analyze the problem of quantum-limited estimation of a stochastically
varying phase of a continuous beam (rather than a pulse) of the electromagnetic
field. We consider both non-adaptive and adaptive measurements, and both dyne
detection (using a local oscillator) and interferometric detection. We take the
phase variation to be \dot\phi = \sqrt{\kappa}\xi(t), where \xi(t) is
\delta-correlated Gaussian noise. For a beam of power P, the important
dimensionless parameter is N=P/\hbar\omega\kappa, the number of photons per
coherence time. For the case of dyne detection, both continuous-wave (cw)
coherent beams and cw (broadband) squeezed beams are considered. For a coherent
beam a simple feedback scheme gives good results, with a phase variance \simeq
N^{-1/2}/2. This is \sqrt{2} times smaller than that achievable by nonadaptive
(heterodyne) detection. For a squeezed beam a more accurate feedback scheme
gives a variance scaling as N^{-2/3}, compared to N^{-1/2} for heterodyne
detection. For the case of interferometry only a coherent input into one port
is considered. The locally optimal feedback scheme is identified, and it is
shown to give a variance scaling as N^{-1/2}. It offers a significant
improvement over nonadaptive interferometry only for N of order unity.Comment: 11 pages, 6 figures, journal versio
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Sand Penetration By High-Speed Projectiles
Tungsten projectiles were shot into sand at velocities between 600 and 2200 m/s. Penetration was maximum at about 775 m/s. Below that velocity, projectiles were apparently stabilized by a fin set. Above that velocity, projectiles were broken by transverse loads. High-speed penetration resulted in comminution of sand particles, reducing their size by about 1000 times.Mechanical Engineerin
Statistical Properties of Many Particle Eigenfunctions
Wavefunction correlations and density matrices for few or many particles are
derived from the properties of semiclassical energy Green functions. Universal
features of fixed energy (microcanonical) random wavefunction correlation
functions appear which reflect the emergence of the canonical ensemble as the
number of particles approaches infinity. This arises through a little known
asymptotic limit of Bessel functions. Constraints due to symmetries,
boundaries, and collisions between particles can be included.Comment: 13 pages, 4 figure
STUDIES ON ABLATION OF OBJECTS TRAVERSING AN ATMOSPHERE
Ablation-type thermal protection of objects traversing an atmosphere - earth and mar
Multiple jet impingement heat transfer characteristic: Experimental investigation of in-line and staggered arrays with crossflow
Heat transfer characteristics were obtained for configurations designed to model the impingement cooled midchord region of air cooled gas turbine airfoils. The configurations tested were inline and staggered two-dimensional arrays of circular jets with ten spanwise rows of holes. The cooling air was constrained to exit in the chordwise direction along the channel formed by the jet orifice plate and the heat transfer surface. Tests were run for chordwise jet hole spacings of five, ten, and fifteen hole diameters; spanwise spacings of four, six, and eight diameters; and channel heights of one, two, three, and six diameters. Mean jet Reynolds numbers ranged from 5000 to 50,000. The thermal boundary condition at the heat transfer test surface was isothermal. Tests were run for sets of geometrically similar configurations of different sizes. Mean and chordwise resolved Nusselt numbers were determined utilizing a specially constructed test surface which was segmented in the chordwise direction
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