228 research outputs found
Finite element modeling for analysis of cracked cylindrical pipes
The characteristic properties of shell element with similar shapes are used to generate a so-called super element for the analysis of the crack problems for cylindrical pressure vessels. The formulation is processed by matrix condensation without the involvement of special treatment. This method can deal with various singularity problems and it also presents excellent results to crack problems for cylindrical shell. Especially, the knowledge of the kind of singular order is not necessary in super element generation; it is very economical in terms of computer memory and programming. This method also exhibits versatility to solve the problem of kinked crack at cylindrical shell
Experimental Entanglement Concentration and Universal Bell-state Synthesizer
We report a novel Bell-state synthesizer in which an interferometric
entanglement concentration scheme is used. An initially mixed polarization
state from type-II spontaneous parametric down-conversion becomes entangled
after the interferometric entanglement concentrator. This Bell-state
synthesizer is universal in the sense that the output polarization state is not
affected by spectral filtering, crystal thickness, and, most importantly, the
choice of pump source. It is also robust against environmental disturbance and
a more general state, partially mixedpartially entangled state, can be
readily generated as well.Comment: Minor update (Newer data
First-order interference of nonclassical light emitted spontaneously at different times
We study first-order interference in spontaneous parametric down-conversion
generated by two pump pulses that do not overlap in time. The observed
modulation in the angular distribution of the signal detector counting rate can
only be explained in terms of a quantum mechanical description based on
biphoton states. The condition for observing interference in the signal channel
is shown to depend on the parameters of the idler radiation.Comment: 5 pages, two-column, submitted to PR
Quantum interference with beamlike type-II spontaneous parametric down-conversion
We implement experimentally a method to generate photon-numberpath and
polarization entangled photon pairs using ``beamlike'' type-II spontaneous
parametric down-conversion (SPDC), in which the signal-idler photon pairs are
emitted as two separate circular beams with small emission angles rather than
as two diverging cones.Comment: 4 pages, two-colum
Quantum diffraction and interference of spatially correlated photon pairs generated by spontaneous parametric down-conversion
We demonstrate one- and two-photon diffraction and interference experiments
utilizing parametric down-converted photon pairs (biphotons) and a transmission
grating. With two-photon detection, the biphoton exhibits a
diffraction-interference pattern equivalent to that of an effective single
particle that is associated with half the wavelength of the constituent
photons. With one-photon detection, however no diffraction-interference pattern
is observed. We show that these phenomena originate from the spatial quantum
correlation between the down-converted photons.Comment: 4 pages, 5 figure
Spectroscopy by frequency entangled photon pairs
Quantum spectroscopy was performed using the frequency-entangled broadband
photon pairs generated by spontaneous parametric down-conversion. An absorptive
sample was placed in front of the idler photon detector, and the frequency of
signal photons was resolved by a diffraction grating. The absorption spectrum
of the sample was measured by counting the coincidences, and the result is in
agreement with the one measured by a conventional spectrophotometer with a
classical light source.Comment: 11 pages, 5 figures, to be published in Phys. Lett.
Demonstration of Feed-Forward Control for Linear Optics Quantum Computation
One of the main requirements in linear optics quantum computing is the
ability to perform single-qubit operations that are controlled by classical
information fed forward from the output of single photon detectors. These
operations correspond to pre-determined combinations of phase corrections and
bit-flips that are applied to the post-selected output modes of
non-deterministic quantum logic devices. Corrections of this kind are required
in order to obtain the correct logical output for certain detection events, and
their use can increase the overall success probability of the devices. In this
paper, we report on the experimental demonstration of the use of this type of
feed-forward system to increase the probability of success of a simple
non-deterministic quantum logic operation from approximately 1/4 to 1/2. This
logic operation involves the use of one target qubit and one ancilla qubit
which, in this experiment, are derived from a parametric down-conversion photon
pair. Classical information describing the detection of the ancilla photon is
fed-forward in real-time and used to alter the quantum state of the output
photon. A fiber optic delay line is used to store the output photon until a
polarization-dependent phase shift can be applied using a high speed Pockels
cell
Interferometric Bell-state preparation using femtosecond-pulse-pumped Spontaneous Parametric Down-Conversion
We present theoretical and experimental study of preparing maximally
entangled two-photon polarization states, or Bell states, using femtosecond
pulse pumped spontaneous parametric down-conversion (SPDC). First, we show how
the inherent distinguishability in femtosecond pulse pumped type-II SPDC can be
removed by using an interferometric technique without spectral and amplitude
post-selection. We then analyze the recently introduced Bell state preparation
scheme using type-I SPDC. Theoretically, both methods offer the same results,
however, type-I SPDC provides experimentally superior methods of preparing Bell
states in femtosecond pulse pumped SPDC. Such a pulsed source of highly
entangled photon pairs is useful in quantum communications, quantum
cryptography, quantum teleportation, etc.Comment: 11 pages, two-column format, to appear in PR
Multi-parameter Entanglement in Quantum Interferometry
The role of multi-parameter entanglement in quantum interference from
collinear type-II spontaneous parametric down-conversion is explored using a
variety of aperture shapes and sizes, in regimes of both ultrafast and
continuous-wave pumping. We have developed and experimentally verified a theory
of down-conversion which considers a quantum state that can be concurrently
entangled in frequency, wavevector, and polarization. In particular, we
demonstrate deviations from the familiar triangular interference dip, such as
asymmetry and peaking. These findings improve our capacity to control the
quantum state produced by spontaneous parametric down-conversion, and should
prove useful to those pursuing the many proposed applications of down-converted
light.Comment: submitted to Physical Review
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