14,725 research outputs found
Confidence and Backaction in the Quantum Filter Equation
We study the confidence and backaction of state reconstruction based on a
continuous weak measurement and the quantum filter equation. As a physical
example we use the traditional model of a double quantum dot being continuously
monitored by a quantum point contact. We examine the confidence of the estimate
of a state constructed from the measurement record, and the effect of
backaction of that measurement on that state. Finally, in the case of general
measurements we show that using the relative entropy as a measure of confidence
allows us to define the lower bound on the confidence as a type of quantum
discord.Comment: 9 pages, 6 figure
An improved solar wind electron-density model for pulsar timing
Variations in the solar wind density introduce variable delays into pulsar
timing observations. Current pulsar timing analysis programs only implement
simple models of the solar wind, which not only limit the timing accuracy, but
can also affect measurements of pulsar rotational, astrometric and orbital
parameters. We describe a new model of the solar wind electron density content
which uses observations from the Wilcox Solar Observatory of the solar magnetic
field. We have implemented this model into the tempo2 pulsar timing package. We
show that this model is more accurate than previous models and that these
corrections are necessary for high precision pulsar timing applications.Comment: Accepted by ApJ, 13 pages, 4 figure
Quantum theory for mesoscopic electric circuits
A quantum theory for mesoscopic electric circuits in accord with the
discreteness of electric charges is proposed. On the basis of the theory,
Schr\"{o}dinger equation for the quantum LC-design and L-design is solved
exactly. The uncertainty relation for electric charge and current is obtained
and a minimum uncertainty state is solved. By introducing a gauge field, a
formula for persistent current arising from magnetic flux is obtained from a
new point of view.Comment: revtex, no figure
Robust stationary entanglement of two coupled qubits in independent environments
The dissipative dynamics of two interacting qubits coupled to independent
reservoirs at nonzero temperatures is investigated, paying special attention to
the entanglement evolution. The counter-rotating terms in the qubit-qubit
interaction give rise to stationary entanglement, traceable back to the ground
state structure. The robustness of this entanglement against thermal noise is
thoroughly analyzed, establishing that it can be detected at reasonable
experimental temperatures. Some effects linked to a possible reservoir
asymmetry are brought to light.Comment: 8 pages, 6 figures; version accepted for publication on Eur. Phys. J.
Tube choledochoureterostomy: A simple method for bile diversion
A technique of bile diversion by tube choledochoureterostomy has been devised for the purpose of studying the role of bile in the intestinal absorption of drugs. This method was used in six dogs. No technical difficulties or major complications developed, as are inevitable with alternative methods, including external fistula. © 1990 Informa UK Ltd All rights reserved: reproduction in whole or part not permitted
An Optical and X-ray Examination of Two Radio Supernova Remnant Candidates in 30 Doradus
The giant HII region 30 Doradus is known for its violent internal motions and
bright diffuse X-ray emission, suggesting the existence of supernova remnants
(SNRs), but no nonthermal radio emission has been detected. Recently, Lazendic
et al. compared the H-alpha/H-beta and radio/H-alpha ratios and suggested two
small radio sources to be nonthermal and thus SNR candidates; however, no
optical or X-ray counterparts were detected. We have used high-resolution
optical images and high-dispersion spectra to examine the morphological,
spectral, and kinematic properties of these two SNR candidates, and still find
no optical evidence supporting their identification as SNRs. We have also
determined the X-ray luminosities of these SNR candidates, and find them 1-3
orders of magnitude lower than those commonly seen in young SNRs. High
extinction can obscure optical and X-ray signatures of an SNR, but would
prohibit the use of a high radio/H-alpha ratio to identify nonthermal radio
emission. We suggest that the SNR candidate MCRX J053831.8-690620 is associated
with a young star forming region; while the radio emission originates from the
obscured star forming region, the observed optical emission is dominated by the
foreground. We suggest that the SNR candidate MCRX J053838.8-690730 is
associated with a dust/molecular cloud, which obscures some optical emission
but not the radio emission.Comment: 13 pages, 2 figures, accepted for publication in the ApJ, Nov 10,
200
Physical Structure of Planetary Nebulae. I. The Owl Nebula
The Owl Nebula is a triple-shell planetary nebula with the outermost shell
being a faint bow-shaped halo. We have obtained deep narrow-band images and
high-dispersion echelle spectra in the H-alpha, [O III], and [N II] emission
lines to determine the physical structure of each shell in the nebula. These
spatio-kinematic data allow us to rule out hydrodynamic models that can
reproduce only the nebular morphology. Our analysis shows that the inner shell
of the main nebula is slightly elongated with a bipolar cavity along its major
axis, the outer nebula is a filled envelope co-expanding with the inner shell
at 40 km/s, and the halo has been braked by the interstellar medium as the Owl
Nebula moves through it. To explain the morphology and kinematics of the Owl
Nebula, we suggest the following scenario for its formation and evolution. The
early mass loss at the TP-AGB phase forms the halo, and the superwind at the
end of the AGB phase forms the main nebula. The subsequent fast stellar wind
compressed the superwind to form the inner shell and excavated an elongated
cavity at the center, but has ceased in the past. At the current old age, the
inner shell is backfilling the central cavity.Comment: 10 pages, 6 figures, 1 table, to appear in the Astronomical Journa
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