2,629 research outputs found
Estimating the metric in curved spacetime with quantum fields
The geometry of space‐time is determined by physical measurements made with clocks and rulers. In so far as these are physical systems, the ultimate accuracy achievable is determined by quantum mechanics. In this paper we use methods from quantum parameter estimation theory to obtain uncertainty principles constraining how well we can estimate the components of a metric tensor using quantum field states propagating in curved space‐time, which is treated entirely classically
Quantum Communication with an Accelerated Partner
An unsolved problem in relativistic quantum information research is how to
model efficient, directional quantum communication between localised parties in
a fully quantum field theoretical framework. We propose a tractable approach to
this problem based on solving the Heisenberg evolution of localized field
observables. We illustrate our approach by analysing, and obtaining approximate
analytical solutions to, the problem of communicating coherent states between
an inertial sender, Alice and an accelerated receiver, Rob. We use these
results to determine the efficiency with which continuous variable quantum key
distribution could be carried out over such a communication channel.Comment: Additional explanatory text and typo in Eq.17 correcte
Quantum Estimation of Parameters of Classical Spacetimes
We describe a quantum limit to measurement of classical spacetimes.
Specifically, we formulate a quantum Cramer-Rao lower bound for estimating the
single parameter in any one-parameter family of spacetime metrics. We employ
the locally covariant formulation of quantum field theory in curved spacetime,
which allows for a manifestly background-independent derivation. The result is
an uncertainty relation that applies to all globally hyperbolic spacetimes.
Among other examples, we apply our method to detection of gravitational waves
using the electromagnetic field as a probe, as in laser-interferometric
gravitational-wave detectors. Other applications are discussed, from
terrestrial gravimetry to cosmology.Comment: 23 pages. This article supersedes arXiv:1108.522
Quantum Connectivity of Space-Time and Gravitationally Induced Decorrelation of Entanglement
We discuss an alternative formulation of the problem of quantum optical
fields in a curved space-time using localized operators. We contrast the new
formulation with the standard approach and find observable differences for
entangled states. We propose an experiment in which an entangled pair of
optical pulses are propagated through non-uniform gravitational fields and find
that the new formulation predicts de-correlation of the optical entanglement
under experimentally realistic conditions
Excitation and Disruption of a Giant Molecular Cloud by the Supernova Remnant 3C391
Using the IRAM 30-m telescope, we observed the supernova remnant 3C 391
(G31.9+0.0) and its surroundings in the CO(2-1), HCO+(1-0), CS(2-1), CS(3-2),
and CS(5-4) lines. The ambient molecular gas at the distance (9 kpc) of the
remnant comprises a giant molecular cloud whose edge is closely parallel to a
ridge of bright non-thermal radio continuum, which evidently delineates the
blast-wave into the cloud. We found that in a small (0.6 pc) portion of the
radio shell, the molecular line profiles consist of a narrow (2 km/s)
component, plus a very wide (> 20 km/s) component. Both spectral components
peak within 20" of a previously-detected OH 1720 MHz maser. We name this source
3C 391:BML (broad molecular line); it provides a new laboratory, similar to IC
443 but on a larger scale, to study shock interactions with dense molecular
gas. The wide spectral component is relatively brighter in the
higher-excitation lines. We interpret the wide spectral component as post-shock
gas, either smoothly accelerated or partially dissociated and reformed behind
the shock. The narrow component is either the pre-shock gas or cold gas
reformed behind a fully dissociative shock. Using the 3 observed CS lines, we
measured the temperature, CS column density, and H2 volume density in a dense
clump in the parent molecular cloud as well as the wide-line and narrow-line
portions of the shocked clump. The physical conditions of the narrow-line gas
are comparable to the highest-density clumps in the giant molecular cloud,
while the wide-line gas is both warmer and denser. The mass of compressed gas
in 3C 391:BML is high enough that its self-gravity is significant, and
eventually it could form one or several stars
The Infrared Properties of Submillimeter Galaxies: Clues From Ultra-Deep 70 Micron Imaging
We present 70 micron properties of submillimeter galaxies (SMGs) in the Great
Observatories Origins Deep Survey (GOODS) North field. Out of thirty
submillimeter galaxies (S_850 > 2 mJy) in the central GOODS-N region, we find
two with secure 70 micron detections. These are the first 70 micron detections
of SMGs. One of the matched SMGs is at z ~ 0.5 and has S_70/S_850 and S_70/S_24
ratios consistent with a cool galaxy. The second SMG (z = 1.2) has
infrared-submm colors which indicate it is more actively forming stars. We
examine the average 70 micron properties of the SMGs by performing a stacking
analysis, which also allows us to estimate that S_850 > 2 mJy SMGs contribute 9
+- 3% of the 70 micron background light. The S_850/S_70 colors of the SMG
population as a whole is best fit by cool galaxies, and because of the
redshifting effects these constraints are mainly on the lower z sub-sample. We
fit Spectral Energy Distributions (SEDs) to the far-infrared data points of the
two detected SMGs and the average low redshift SMG (z_{median}= 1.4). We find
that the average low-z SMG has a cooler dust temperature than local
ultraluminous infrared galaxies (ULIRGs) of similar luminosity and an SED which
is best fit by scaled up versions of normal spiral galaxies. The average low-z
SMG is found to have a typical dust temperature T = 21 -- 33 K and infrared
luminosity L_{8-1000 micron} = 8.0 \times 10^11 L_sun. We estimate the AGN
contribution to the total infrared luminosity of low-z SMGs is less than 23%.Comment: Accepted by ApJ. 14 pages, 6 figures. Minor revisions 20th Dec 200
Infrared and radio observations of W51: Another Orion-KL at a distance of 7kpc
The bright infrared sources W51-IRS2 has at least three components with different physical and evolutionary properties. The spatial distribution and the near infrared spectra of the components in IRS2 are remarkably similar to, but more luminous than those found in Orion, where an H2 region of comparable linear size is also located close to a cluster of compact infrared sources. The characteristics of the nearby W51-NORTH H2O maser source, and the detection of 2 micro m H2 quadrupole emission in IRS2 indicate that the mass loss phenomena found in Orion-KL also exist in W51
The faint counterparts of MAMBO mm sources near the NTT Deep Field
We discuss identifications for 18 sources from our MAMBO 1.2mm survey of the
region surrounding the NTT Deep Field. We have obtained accurate positions from
Very Large Array 1.4GHz interferometry and in a few cases IRAM mm
interferometry, and have also made deep BVRIzJK imaging at ESO. We find
thirteen 1.2mm sources associated with optical/near-infrared objects in the
magnitude range K=19.0 to 22.5, while five are blank fields at K>22. The median
redshift of the radio-identified mm sources is ~2.6 from the radio/mm
estimator, and the median optical/near-infrared photometric redshifts for the
objects with counterparts ~2.1. This suggests that those radio-identified mm
sources without optical/near-infrared counterparts tend to lie at higher
redshifts than those with optical/near-infrared counterparts. Compared to
published identifications of objects from 850micron surveys of similar depth,
the median K and I magnitudes of our counterparts are roughly two magnitudes
fainter and the dispersion of I-K colors is less. Real differences in the
median redshifts, residual mis-identifications with bright objects, cosmic
variance, and small number statistics are likely to contribute to this
significant difference, which also affects redshift measurement strategies. We
discuss basic properties of the near-infrared/(sub)mm/radio spectral energy
distributions of our galaxies and of interferometrically identified submm
sources from the literature. From a comparison with submm objects with
CO-confirmed spectroscopic redshifts we argue that roughly two thirds of the
(sub)mm galaxies are at z>~2.5. This fraction is probably larger when including
sources without radio counterparts. (abridged)Comment: 45 pages, 9 figures. Accepted by ApJ. The resolution of figures 2 and
3 has been degraded. A higher quality pdf version of this paper is available
at http://www.mpe.mpg.de/~dannerb
The Stability of Radiatively Cooled Jets in Three Dimensions
The effect of optically thin radiative cooling on the Kelvin-Helmholtz
instability of three dimensional jets is investigated via linear stability
theory and nonlinear hydrodynamical simulation. Two different cooling functions
are considered: radiative cooling is found to have a significant effect on the
stability of the jet in each case. The wavelengths and growth rates of unstable
modes in the numerical simulations are found to be in good agreement with
theoretical predictions. Disruption of the jet is found to be sensitive to the
precessional frequency at the origin with lower frequencies leading to more
rapid disruption. Strong nonlinear effects are observed as the result of the
large number of normal modes in three dimensions which provide rich mode-mode
interactions. These mode-mode interactions provide new mechanisms for the
formation of knots in the flows. Significant structural features found in the
numerical simulations appear similar to structures observed on protostellar
jets.Comment: 32 pages, 13 figures, figures included in page tota
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