1,739 research outputs found
Physical limitations on quantum nonlocality in the detection of gamma photons emitted from positron/electron annihilation
Recent experimental measurements of the time interval between detection of
the two photons emitted in positron/electron annihilation have indicated that
collapse of the spatial part of the photon's wavefunction, due to detection of
the other photon, does not occur. Although quantum nonlocality actually occurs
in photons produced through parametric down-conversion, the recent experiments
give strong evidence against measurement-induced instantaneous
spatial-localization of high-energy gamma photons. A new quantum-mechanical
analysis of the EPR problem is presented which may help to explain the observed
differences between photons produced through parametric down-conversion and
photons produced through positron/electron annihilation. The results are found
to concur with the recent experiments involving gamma photons.Comment: accepted for publication, Phys. Rev.
Cyclical Quantum Memory for Photonic Qubits
We have performed a proof-of-principle experiment in which qubits encoded in
the polarization states of single-photons from a parametric down-conversion
source were coherently stored and read-out from a quantum memory device. The
memory device utilized a simple free-space storage loop, providing a cyclical
read-out that could be synchronized with the cycle time of a quantum computer.
The coherence of the photonic qubits was maintained during switching operations
by using a high-speed polarizing Sagnac interferometer switch.Comment: 4 pages, 5 figure
Heralding Single Photons from Pulsed Parametric Down-Conversion
We describe an experiment in which photon pairs from a pulsed parametric
down-conversion source were coupled into single-mode fibers. Detecting one of
the photons heralded the presence of the other photon in its fiber with a
probability of 83%. The heralded photons were then used in a simple
multi-photon interference experiment to illustrate their potential for quantum
information applications.Comment: 4 pages, 7 figures. Version 2 has minor revision
Note on the energy-momentum tensor for general mixed tensor-spinor fields
This note provides an explicit proof of the equivalence of the Belinfante's
energy-momentum tensor and the metric energy-momentum tensor for general mixed
tensor-spinor fields.Comment: 7 pages, title changed, typos corrected, accepted for publication in
Communications in Theoretical Physic
Open String Star as a Continuous Moyal Product
We establish that the open string star product in the zero momentum sector
can be described as a continuous tensor product of mutually commuting two
dimensional Moyal star products. Let the continuous variable parametrize the eigenvalues of the Neumann matrices; then the
noncommutativity parameter is given by .
For each , the Moyal coordinates are a linear combination of even
position modes, and the Fourier transform of a linear combination of odd
position modes. The commuting coordinate at is identified as the
momentum carried by half the string. We discuss the relation to Bars' work, and
attempt to write the string field action as a noncommutative field theory.Comment: 30 pages, LaTeX. One reference adde
Long-term solar activity influences on South American rivers
River streamflows are excellent climatic indicators since they integrate
precipitation over large areas. Here we follow up on our previous study of the
influence of solar activity on the flow of the Parana River, in South America.
We find that the unusual minimum of solar activity in recent years have a
correlation on very low levels in the Parana's flow, and we report historical
evidence of low water levels during the Little Ice Age. We also study data for
the streamflow of three other rivers (Colorado, San Juan and Atuel), and snow
levels in the Andes. We obtained that, after eliminating the secular trends and
smoothing out the solar cycle, there is a strong positive correlation between
the residuals of both the Sunspot Number and the streamflows, as we obtained
for the Parana. Both results put together imply that higher solar activity
corresponds to larger precipitation, both in summer and in wintertime, not only
in the large basin of the Parana, but also in the Andean region north of the
limit with Patagonia.Comment: Accepted to publication by Journal of Atmospheric and
Solar-Terrestrial Physic
Recommended from our members
Plutonium dioxide dissolution in glass
In the aftermath of the Cold War, the U.S. Department of Energy`s (DOE) Office of Fissile Materials Disposition (OFMD) is charged with providing technical support for evaluation of disposition options for excess fissile materials manufactured for the nation`s defense. One option being considered for the disposition of excess plutonium (Pu) is immobilization by vitrification. The vitrification option entails immobilizing Pu in a host glass and waste package that are criticality-safe (immune to nuclear criticality), proliferation-resistant, and environmentally acceptable for long-term storage or disposal. To prove the technical and economic feasibility of candidate vitrification options it is necessary to demonstrate that PuO{sub 2} feedstock can be dissolved in glass in sufficient quantity. The OFMD immobilization program has set a Pu solubility goal of 10 wt% in glass. The life cycle cost of the vitrification options are strongly influenced by the rate at which PUO{sub 2} dissolves in glass. The total number of process lines needed for vitrification of 50 t of Pu in 10 years is directly dependent upon the time required for Pu dissolution in glass. The objective of this joint Pacific Northwest National Laboratory (PNNL) - Savannah River Technology Center (SRTC) study was to demonstrate a high Pu solubility in glass and to identify on a rough scale the time required for Pu dissolution in the glass. This study was conducted using a lanthanide borosilicate (LaBS) glass composition designed at the SRTC for the vitrification of actinides
Chern-Simons Vortices in Supergravity
We study supersymmetric vortex solutions in three-dimensional abelian gauged
supergravity. First, we construct the general U(1)-gauged D=3, N=2 supergravity
whose scalar sector is an arbitrary Kahler manifold with U(1) isometry. This
construction clarifies the connection between local supersymmetry and the
specific forms of some scalar potentials previously found in the literature --
in particular, it provides the locally supersymmetric embedding of the abelian
Chern-Simons Higgs model. We show that the Killing spinor equations admit
rotationally symmetric vortex solutions with asymptotically conical geometry
which preserve half of the supersymmetry.Comment: 26 pages, LaTeX2
Global embeddings of scalar-tensor theories in (2+1)-dimensions
We obtain (3+3)- or (3+2)-dimensional global flat embeddings of four
uncharged and charged scalar-tensor theories with the parameters B or L in the
(2+1)-dimensions, which are the non-trivially modified versions of the
Banados-Teitelboim-Zanelli (BTZ) black holes. The limiting cases B=0 or L=0
exactly are reduced to the Global Embedding Minkowski Space (GEMS) solution of
the BTZ black holes.Comment: 19 pages, 2 figure
Single Photons on Pseudo-Demand from Stored Parametric Down-Conversion
We describe the results of a parametric down-conversion experiment in which
the detection of one photon of a pair causes the other photon to be switched
into a storage loop. The stored photon can then be switched out of the loop at
a later time chosen by the user, providing a single photon for potential use in
a variety of quantum information processing applications. Although the stored
single photon is only available at periodic time intervals, those times can be
chosen to match the cycle time of a quantum computer by using pulsed
down-conversion. The potential use of the storage loop as a photonic quantum
memory device is also discussed.Comment: 8 pages, 7 Figs., RevTe
- …