5,027 research outputs found
Isolated Photons in Deep Inelastic Scattering
Photon radiation at large transverse momenta at colliders is a detailed probe
of hard interaction dynamics. The isolated photon production cross section in
deep inelastic scattering was measured recently by the ZEUS experiment, and
found to be considerably larger than theoretical predictions obtained with
widely used event generators. To investigate this discrepancy, we perform a
dedicated parton-level calculation of this observable, including contributions
from fragmentation and large-angle radiation. Our results are in good agreement
with all aspects of the experimental measurement.Comment: 4 pages, 3 figure
Infinite qubit rings with maximal nearest neighbor entanglement: the Bethe ansatz solution
We search for translationally invariant states of qubits on a ring that
maximize the nearest neighbor entanglement. This problem was initially studied
by O'Connor and Wootters [Phys. Rev. A {\bf 63}, 052302 (2001)]. We first map
the problem to the search for the ground state of a spin 1/2 Heisenberg XXZ
model. Using the exact Bethe ansatz solution in the limit of an infinite ring,
we prove the correctness of the assumption of O'Connor and Wootters that the
state of maximal entanglement does not have any pair of neighboring spins
``down'' (or, alternatively spins ``up''). For sufficiently small fixed
magnetization, however, the assumption does not hold: we identify the region of
magnetizations for which the states that maximize the nearest neighbor
entanglement necessarily contain pairs of neighboring spins ``down''.Comment: 10 pages, 4 figures; Eq. (45) and Fig. 3 corrected, no qualitative
change in conclusion
Lapex: A Phoswich balloon experiment for hard X-ray astronomy
Satellite and balloon observations have shown that several classes of celestial objects are hard ( 15 keV) energy band with a sensitivity of approx 10 mCrab has been performed with the UCSD/MIT instrument (A4) on board the HEAO 1 satellite. About 70 X-ray sources were detected, including galactic and extragalactic objects. Hard X-ray emission has been detected in the Galaxy from X-ray pulsars. Extragalactic sources of hard X-ray emission include clusters of galaxies, QSOs, BL Lac objects, Seyfert galaxies. The essential characteristics of the Large Area Phoswich Experiment (LAPEX) for crowded sky field observations are described. It has: (1) a broad energy band of operation (20-300 keV); (2) a 3 sigma sensitivity of about 1 mCrab in 10,000 s of live observing time; and (3) imaging capabilities with an angular resolution of about 20'
Differential atom interferometry beyond the standard quantum limit
We analyze methods to go beyond the standard quantum limit for a class of
atomic interferometers, where the quantity of interest is the difference of
phase shifts obtained by two independent atomic ensembles. An example is given
by an atomic Sagnac interferometer, where for two ensembles propagating in
opposite directions in the interferometer this phase difference encodes the
angular velocity of the experimental setup. We discuss methods of squeezing
separately or jointly observables of the two atomic ensembles, and compare in
detail advantages and drawbacks of such schemes. In particular we show that the
method of joint squeezing may improve the variance by up to a factor of 2. We
take into account fluctuations of the number of atoms in both the preparation
and the measurement stage, and obtain bounds on the difference of the numbers
of atoms in the two ensembles, as well as on the detection efficiency, which
have to be fulfilled in order to surpass the standard quantum limit. Under
realistic conditions, the performance of both schemes can be improved
significantly by reading out the phase difference via a quantum non-demolition
(QND) measurement. Finally, we discuss a scheme using macroscopically entangled
ensembles.Comment: 10 pages, 5 figures; eq. (3) corrected and other minor change
Simulation of modern and middle Cretaceous marine ÎŽ 18 O with an oceanâatmosphere general circulation model
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/95522/1/palo1494.pd
Electrical manipulation of spin states in a single electrostatically gated transition-metal complex
We demonstrate an electrically controlled high-spin (S=5/2) to low-spin
(S=1/2) transition in a three-terminal device incorporating a single Mn2+ ion
coordinated by two terpyridine ligands. By adjusting the gate-voltage we reduce
the terpyridine moiety and thereby strengthen the ligand-field on the Mn-atom.
Adding a single electron thus stabilizes the low-spin configuration and the
corresponding sequential tunnelling current is suppressed by spin-blockade.
From low-temperature inelastic cotunneling spectroscopy, we infer the
magnetic excitation spectrum of the molecule and uncover also a strongly
gate-dependent singlet-triplet splitting on the low-spin side. The measured
bias-spectroscopy is shown to be consistent with an exact diagonalization of
the Mn-complex, and an interpretation of the data is given in terms of a
simplified effective model.Comment: Will appear soon in Nanoletter
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