9,453 research outputs found
Comment on "Self-Purification in Semiconductor Nanocrystals"
In a recent Letter [PRL 96, 226802 (2006)], Dalpian and Chelikowsky claimed
that formation energies of Mn impurities in CdSe nanocrystals increase as the
size of the nanocrystal decreases, and argued that this size dependence leads
to "self-purification" of small nanocrystals. They presented
density-functional-theory (DFT) calculations showing a strong size dependence
for Mn impurity formation energies, and proposed a general explanation. In this
Comment we show that several different DFT codes, pseudopotentials, and
exchange-correlation functionals give a markedly different result: We find no
such size dependence. More generally, we argue that formation energies are not
relevant to substitutional doping in most colloidally grown nanocrystals.Comment: 1 page, 1 figur
The ATLAS-SPT Radio Survey of Cluster Galaxies
Using a high-performance computing cluster to mosaic 4,787 pointings, we have
imaged the 100 sq. deg. South Pole Telescope (SPT) deep-field at 2.1 GHz using
the Australian Telescope Compact Array to an rms of 80 Jy and a resolution
of 8". Our goal is to generate an independent sample of radio-selected galaxy
clusters to study how the radio properties compare with cluster properties at
other wavelengths, over a wide range of redshifts in order to construct a
timeline of their evolution out to . A preliminary analysis of the
source catalogue suggests there is no spatial correlation between the clusters
identified in the SPT-SZ catalogue and our wide-angle tail galaxies.Comment: 9 pages, 4 figures. Submitted to Proceedings of Science for "The many
facets of extragalactic radio surveys: towards new scientific challenges",
Bologna, Italy 20-23 October 2015 (EXTRA-RADSUR2015
The Spatial Correlation of Bent-Tail Galaxies and Galaxy Clusters
We have completed a deep radio continuum survey covering 86 square degrees of
the Spitzer-South Pole Telescope deep field to test whether bent-tail galaxies
are associated with galaxy clusters. We present a new catalogue of 22 bent-tail
galaxies and a further 24 candidate bent-tail galaxies. Surprisingly, of the 8
bent-tail galaxies with photometric redshifts, only two are associated with
known clusters. While the absence of bent-tail sources in known clusters may be
explained by effects such as sensitivity, the absence of known clusters
associated with most bent-tail galaxies casts doubt upon current models of
bent-tail galaxies.Comment: Accepted by MNRA
Atom detection in a two-mode optical cavity with intermediate coupling: Autocorrelation studies
We use an optical cavity in the regime of intermediate coupling between atom
and cavity mode to detect single moving atoms. Degenerate polarization modes
allow excitation of the atoms in one mode and collection of spontaneous
emission in the other, while keeping separate the two sources of light; we
obtain a higher confidence and efficiency of detection by adding
cavity-enhanced Faraday rotation. Both methods greatly benefit from coincidence
detection of photons, attaining fidelities in excess of 99% in less than 1
microsecond. Detailed studies of the second-order intensity autocorrelation
function of light from the signal mode reveal evidence of antibunched photon
emissions and the dynamics of single-atom transits.Comment: 10 pages, 10 figures, to be published in Phys. Rev.
Observation of ground-state quantum beats in atomic spontaneous emission
We report ground-state quantum beats in spontaneous emission from a
continuously driven atomic ensemble. Beats are visible only in an intensity
autocorrelation and evidence spontaneously generated coherence in radiative
decay. Our measurement realizes a quantum eraser where a first photon detection
prepares a superposition and a second erases the "which-path" information in
the intermediate state.Comment: 4 pages, 4 figures, to appear in Phys. Rev. Letter
Infrared-Faint Radio Sources: A New Population of High-redshift Radio Galaxies
We present a sample of 1317 Infrared-Faint Radio Sources (IFRSs) that, for
the first time, are reliably detected in the infrared, generated by
cross-correlating the Wide-Field Infrared Survey Explorer (WISE) all-sky survey
with major radio surveys. Our IFRSs are brighter in both radio and infrared
than the first generation IFRSs that were undetected in the infrared by the
Spitzer Space Telescope. We present the first spectroscopic redshifts of IFRSs,
and find that all but one of the IFRSs with spectroscopy has z > 2. We also
report the first X-ray counterparts of IFRSs, and present an analysis of radio
spectra and polarization, and show that they include Gigahertz-Peaked Spectrum,
Compact Steep Spectrum, and Ultra-Steep Spectrum sources. These results,
together with their WISE infrared colours and radio morphologies, imply that
our sample of IFRSs represents a population of radio-loud Active Galactic
Nuclei at z > 2. We conclude that our sample consists of lower-redshift
counterparts of the extreme first generation IFRSs, suggesting that the fainter
IFRSs are at even higher redshift.Comment: 23 pages, 17 figures. Submitted to MNRA
From quantum feedback to probabilistic error correction: Manipulation of quantum beats in cavity QED
It is shown how to implement quantum feedback and probabilistic error
correction in an open quantum system consisting of a single atom, with ground-
and excited-state Zeeman structure, in a driven two-mode optical cavity. The
ground state superposition is manipulated and controlled through conditional
measurements and external fields, which shield the coherence and correct
quantum errors. Modeling of an experimentally realistic situation demonstrates
the robustness of the proposal for realization in the laboratory
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