6,083 research outputs found
Spin correlated interferometry for polarized and unpolarized photons on a beam splitter
Spin interferometry of the 4th order for independent polarized as well as
unpolarized photons arriving simultaneously at a beam splitter and exhibiting
spin correlation while leaving it, is formulated and discussed in the quantum
approach. Beam splitter is recognized as a source of genuine singlet photon
states. Also, typical nonclassical beating between photons taking part in the
interference of the 4th order is given a polarization dependent explanation.Comment: RevTeX, 19 pages, 1 ps figure, author web page at
http://m3k.grad.hr/pavici
Reversible Embedding to Covers Full of Boundaries
In reversible data embedding, to avoid overflow and underflow problem, before
data embedding, boundary pixels are recorded as side information, which may be
losslessly compressed. The existing algorithms often assume that a natural
image has little boundary pixels so that the size of side information is small.
Accordingly, a relatively high pure payload could be achieved. However, there
actually may exist a lot of boundary pixels in a natural image, implying that,
the size of side information could be very large. Therefore, when to directly
use the existing algorithms, the pure embedding capacity may be not sufficient.
In order to address this problem, in this paper, we present a new and efficient
framework to reversible data embedding in images that have lots of boundary
pixels. The core idea is to losslessly preprocess boundary pixels so that it
can significantly reduce the side information. Experimental results have shown
the superiority and applicability of our work
Hertz-level Measurement of the 40Ca+ 4s 2S1/2-3d 2D5/2 Clock Transition Frequency With Respect to the SI Second through GPS
We report a frequency measurement of the clock transition of a single ^40Ca^+
ion trapped and laser cooled in a miniature ring Paul trap with 10^-15 level
uncertainty. In the measurement, we used an optical frequency comb referenced
to a Hydrogen maser, which was calibrated to the SI second through the Global
Positioning System (GPS). Two rounds of measurements were taken in May and June
2011, respectively. The frequency was measured to be 411 042 129 776 393.0(1.6)
Hz with a fractional uncertainty of 3.9{\times}10^-15 in a total averaging time
of > 2{\times}10^6 s within 32 days
Demonstration of Controllable Temporal Distinguishability in a Three-Photon State
Multi-photon interference is at the heart of the recently proposed linear
optical quantum computing scheme and plays an essential role in many protocols
in quantum information. Indistinguishability is what leads to the effect of
quantum interference. Optical interferometers such as Michaelson interferometer
provide a measure for second-order coherence at one-photon level and
Hong-Ou-Mandel interferometer was widely employed to describe two-photon
entanglement and indistinguishability. However, there is not an effective way
for a system of more than two photons. Recently, a new interferometric scheme
was proposed to quantify the degree of multi-photon distinguishability. Here we
report an experiment to implement the scheme for three-photon case. We are able
to generate three photons with different degrees of temporal distinguishability
and demonstrate how to characterize them by the visibility of three-photon
interference. This method of quantitative description of multi-photon
indistinguishability will have practical implications in the implementation of
quantum information protocols
Evaluation of deformation stability and fracture mechanism in incremental sheet forming
Incremental sheet forming (ISF) is a flexible process for rapid manufacturing of complex sheet metal parts. An advantage of ISF is the improved formability than traditional sheet forming processes such as stamping. A number of fundamental studies have been conducted to investigate the enhanced ISF formability considering the effects such as bending under tension and through thickness shear. To further understand the ISF deformation mechanism and formability enhancement, this work presents a new analytical model which is focused on investigating the deformation stability and its effect on the metal sheet fracture. Based on this new model, the critical strain of deformation instability is obtained. Furthermore, influences of the work-hardening effect and bending effect on the deformation stability are investigated. To validate the analytical model, the fracture occurrence of two aluminum grades, AA1100 and AA5052, are investigated by using ISF experiment. Based on the analytical and experimental investigation, this study has concluded that bending plays a major role on ISF deformation stability. In addition, the ISF fracture depends on both deformation stability and the sheet material's ductility
Theory on quench-induced pattern formation: Application to the isotropic to smectic-A phase transitions
During catastrophic processes of environmental variations of a thermodynamic
system, such as rapid temperature decreasing, many novel and complex patterns
often form.
To understand such phenomena, a general mechanism is proposed based on the
competition between heat transfer and conversion of heat to other energy forms.
We apply it to the smectic-A filament growth process during quench-induced
isotropic to smectic-A phase transition. Analytical forms for the buckling
patterns are derived and we find good agreement with experimental observation
[Phys. Rev. {\bf E55} (1997) 1655]. The present work strongly indicates that
rapid cooling will lead to structural transitions in the smectic-A filament at
the molecular level to optimize heat conversion. The force associated with this
pattern formation process is estimated to be in the order of
piconewton.Comment: 9 pages in RevTex form, with 3 postscript figures. Accepted by PR
Comment on ``Manipulating the frequency entangled states by an acoutic-optical modulator''
A recent theoretical paper [1] proposes a scheme for entanglement swapping
utilizing acousto-optic modulators without requiring a Bell-state measurement.
In this comment, we show that the proposal is flawed and no entanglement
swapping can occur without measurement.Comment: 6 pages, 2 figures submitted to Phys. Rev
Primary role of the barely occupied states in the charge density wave formation of NbSe2
NbSe2 is a prototypical charge-density-wave (CDW) material, whose mechanism
remains mysterious so far. With angle resolved photoemission spectroscopy, we
mapped out the CDW gap and recovered the long-lost nesting condition over a
large broken-honeycomb region in the Brillouin zone, which consists of six
saddle band point regions with high density of states (DOS), and large regions
away from Fermi surface with negligible DOS at the Fermi energy. We show that
the major contributions to the CDW come from these barely occupied states
rather than the saddle band points. Our findings not only resolve a long
standing puzzle, but also overthrow the conventional wisdom that CDW is
dominated by regions with high DOS.Comment: 5 pages, 4 figure
De Broglie Wavelength of a Nonlocal Four-Photon
Superposition is one of the most distinct features of quantum theory and has
been demonstrated in numerous realizations of Young's classical double-slit
interference experiment and its analogues. However, quantum entanglement - a
significant coherent superposition in multiparticle systems - yields phenomena
that are much richer and more interesting than anything that can be seen in a
one-particle system. Among them, one important type of multi-particle
experiments uses path-entangled number-states, which exhibit pure higher-order
interference and allow novel applications in metrology and imaging such as
quantum interferometry and spectroscopy with phase sensitivity at the
Heisenberg limit or quantum lithography beyond the classical diffraction limit.
Up to now, in optical implementations of such schemes lower-order interference
effects would always decrease the overall performance at higher particle
numbers. They have thus been limited to two photons. We overcome this
limitation and demonstrate a linear-optics-based four-photon interferometer.
Observation of a four-particle mode-entangled state is confirmed by
interference fringes with a periodicity of one quarter of the single-photon
wavelength. This scheme can readily be extended to arbitrary photon numbers and
thus represents an important step towards realizable applications with
entanglement-enhanced performance.Comment: 19 pages, 4 figures, submitted on November 18, 200
Quantum enhancement of N-photon phase sensitivity by interferometric addition of down-converted photon pairs to weak coherent light
It is shown that the addition of down-converted photon pairs to coherent
laser light enhances the N-photon phase sensitivity due to the quantum
interference between components of the same total photon number. Since most of
the photons originate from the coherent laser light, this method of obtaining
non-classical N-photon states is much more efficient than methods based
entirely on parametrically down-converted photons. Specifically, it is possible
to achieve an optimal phase sensitivity of about delta phi^2=1/N^(3/2), equal
to the geometric mean of the standard quantum limit and the Heisenberg limit,
when the average number of down-converted photons contributing to the N-photon
state approaches (N/2)^(1/2).Comment: 21 pages, including 6 figures. Extended version gives more details on
down-conversion efficiencies and clarifies the relation between phase
sensitivity and squeezing. The title has been changed in order to avoid
misunderstandings regarding these concept
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