12,673 research outputs found
High-efficiency cluster-state generation with atomic ensembles via the dipole-blockade mechanism
Get PDFWe demonstrate theoretically a scheme for cluster-state generation, based on atomic ensembles and the dipole-blockade mechanism. In the protocol, atomic ensembles serve as single-qubit systems. Therefore, we review single-qubit operations on qubit defined as collective states of atomic ensemble. Our entangling protocol requires nearly identical single-photon sources, one ultracold ensemble per physical qubit, and regular photodetectors. The general entangling procedure is presented, as well as a procedure that generates in a single step Q-qubit GHZ states with success probability p(success) similar to eta(Q/2), where eta is the combined detection and source efficiency. This is significantly more efficient than any known robust probabilistic entangling operation. GHZ states form the basic building block for universal cluster states, a resource for the one-way quantum computer
Simulation of 2-way fluid structure interaction in a 3D model combustor
Get PDFThe liner of a gas turbine combustor is a very flexible structure that is exposed to the pressure oscillations that occur in the combustor. These pressure oscillations can be of very high amplitude due to thermoacoustic instability, when the fluctuations of the rate of heat release and the acoustic pressure waves amplify each other. The liner structure is a dynamic mechanical system that vibrates at its eigenfrequencies and at the frequencies by which it is forced by the pressure oscillations to which it is exposed. On the other hand the liner vibrations force a displacement of the flue gas near the wall in the combustor. The displacement is very small but this acts like a distributed acoustic source which is proportional to the liner wall acceleration. Hence liner and combustor are a coupled elasto-acoustic system. When this is exposed to a limit cycle oscillation the liner may fail due to fatigue.
In this paper the method and the results will be presented of the partitioned simulation of the coupled acousto-elastic system composed of the liner and the flue gas domain in the combustor. The partitioned simulation uses separate solvers for the flow domain and the structural domain, that operate in a coupled way. In this work 2-way fluid structure interaction is studied for the case of a model combustor for the operating conditions 40–60 kW with equivalence ratio of 0.625. This is done in the framework of the LIMOUSINE project. Computational fluid dynamics analysis is performed to obtain the thermal loading of the combustor liner and finite element analysis renders the temperature, stress distribution and deformation in the liner. The software used is ANSYS workbench V13.0 software, in which the information (pressure and displacement) is also exchanged between fluid and structural domain transiently.</jats:p
The Diffusion of Energy Efficiency in Building
Get PDFWe analyze the diffusion of buildings certified for energy efficiency across US property markets. Using a panel of 48 metropolitan areas (MSAs) observed over the last 15 years, we model the geographic patterns and dynamics of building certification, relating industry composition, changes in economic conditions, characteristics of the local commercial property market, and the presence of human capital, to the cross-sectional variation in energy-efficient building technologies and the diffusion of those technologies over time. Understanding the determinants and the rate at which energy-efficient building practices diffuse is important for designing policies to affect resource consumption in the built environment.
The influence of forward-scattered light in transmission measurements of (exo)planetary atmospheres
Full text link[Abridged] The transmission of light through a planetary atmosphere can be
studied as a function of altitude and wavelength using stellar or solar
occultations, giving often unique constraints on the atmospheric composition.
For exoplanets, a transit yields a limb-integrated, wavelength-dependent
transmission spectrum of an atmosphere. When scattering haze and/or cloud
particles are present in the planetary atmosphere, the amount of transmitted
flux not only depends on the total optical thickness of the slant light path
that is probed, but also on the amount of forward-scattering by the scattering
particles. Here, we present results of calculations with a three-dimensional
Monte Carlo code that simulates the transmitted flux during occultations or
transits. For isotropically scattering particles, like gas molecules, the
transmitted flux appears to be well-described by the total atmospheric optical
thickness. Strongly forward-scattering particles, however, such as commonly
found in atmospheres of Solar System planets, can increase the transmitted flux
significantly. For exoplanets, such added flux can decrease the apparent radius
of the planet by several scale heights, which is comparable to predicted and
measured features in exoplanet transit spectra. We performed detailed
calculations for Titan's atmosphere between 2.0 and 2.8 micron and show that
haze and gas abundances will be underestimated by about 8% if
forward-scattering is ignored in the retrievals. At shorter wavelengths, errors
in the gas and haze abundances and in the spectral slope of the haze particles
can be several tens of percent, also for other Solar System planetary
atmospheres. We also find that the contribution of forward-scattering can be
fairly well described by modelling the atmosphere as a plane-parallel slab.Comment: Icarus, accepted for publicatio
A Quantum Rosetta Stone for Interferometry
Get PDFHeisenberg-limited measurement protocols can be used to gain an increase in
measurement precision over classical protocols. Such measurements can be
implemented using, e.g., optical Mach-Zehnder interferometers and Ramsey
spectroscopes. We address the formal equivalence between the Mach-Zehnder
interferometer, the Ramsey spectroscope, and the discrete Fourier transform.
Based on this equivalence we introduce the ``quantum Rosetta stone'', and we
describe a projective-measurement scheme for generating the desired
correlations between the interferometric input states in order to achieve
Heisenberg-limited sensitivity. The Rosetta stone then tells us the same method
should work in atom spectroscopy.Comment: 8 pages, 4 figure
Wet chemical etching mechanism of silicon
Get PDFWe review what can be said on wet chemical etching of single crystals from the viewpoint of the science of crystal growth. Starting point is that there are smooth and rough crystal surfaces. The kinetics of smooth faces is controlled by a nucleation barrier that is absent on rough faces. The latter therefore etch faster by orders of magnitude. The analysis of the diamond crystal structure reveals that the {111} face is the only smooth face in this lattice-other faces might be smooth only because of surface reconstruction. In this way we explain the minimum of the etch rate in KOH:H2O in the <001> direction. Two critical predictions concerning the shape of the minimum of the etch rate close to <001> and the transition from isotropic to anisotropic etching in HF:HNO3 based solutions are tested experimentally. The results are in-agreement with the theor
Effects of self-phase modulation on weak nonlinear optical quantum gates
Full text linkA possible two-qubit gate for optical quantum computing is the parity gate
based on the weak Kerr effect. Two photonic qubits modulate the phase of a
coherent state, and a quadrature measurement of the coherent state reveals the
parity of the two qubits without destroying the photons. This can be used to
create so-called cluster states, a universal resource for quantum computing.
Here, the effect of self-phase modulation on the parity gate is studied,
introducing generating functions for the Wigner function of a modulated
coherent state. For materials with non-EIT-based Kerr nonlinearities, there is
typically a self-phase modulation that is half the magnitude of the cross-phase
modulation. Therefore, this effect cannot be ignored. It is shown that for a
large class of physical implementations of the phase modulation, the quadrature
measurement cannot distinguish between odd and even parity. Consequently, weak
nonlinear parity gates must be implemented with physical systems where the
self-phase modulation is negligable.Comment: 7 pages, 4 figure
Information gap for classical and quantum communication in a Schwarzschild spacetime
Get PDFCommunication between a free-falling observer and an observer hovering above
the Schwarzschild horizon of a black hole suffers from Unruh-Hawking noise,
which degrades communication channels. Ignoring time dilation, which affects
all channels equally, we show that for bosonic communication using single and
dual rail encoding the classical channel capacity reaches a finite value and
the quantum coherent information tends to zero. We conclude that classical
correlations still exist at infinite acceleration, whereas the quantum
coherence is fully removed.Comment: 5 pages, 4 figure
Super-resolving multi-photon interferences with independent light sources
Full text linkWe propose to use multi-photon interferences from statistically independent
light sources in combination with linear optical detection techniques to
enhance the resolution in imaging. Experimental results with up to five
independent thermal light sources confirm this approach to improve the spatial
resolution. Since no involved quantum state preparation or detection is
required the experiment can be considered an extension of the Hanbury Brown and
Twiss experiment for spatial intensity correlations of order N>2
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