6,900 research outputs found
Trapped-ion quantum error-correcting protocols using only global operations
Quantum error-correcting codes are many-body entangled states that are
prepared and measured using complex sequences of entangling operations. Each
element of such an entangling sequence introduces noise to delicate quantum
information during the encoding or reading out of the code. It is important
therefore to find efficient entangling protocols to avoid the loss of
information. Here we propose an experiment that uses only global entangling
operations to encode an arbitrary logical qubit to either the five-qubit
repetition code or the five-qubit code, with a six-ion Coulomb crystal
architecture in a Penning trap. We show that the use of global operations
enables us to prepare and read out these codes using only six and ten global
entangling pulses, respectively. The proposed experiment also allows the
acquisition of syndrome information during readout. We provide a noise analysis
for the presented protocols, estimating that we can achieve a six-fold
improvement in coherence time with noise as high as on each
entangling operation.Comment: 7 pages, 4 figures, published version, comments are welcom
A synoptic view of solar transient evolution in the inner heliosphere using the Heliospheric Imagers on STEREO
By exploiting data from the STEREO/heliospheric imagers (HI) we extend a well-established technique developed for coronal analysis by producing time-elongation plots that reveal the nature of solar transient activity over a far more extensive region of the heliosphere than previously possible from coronagraph images. Despite the simplicity of these plots, their power in demonstrating how the plethora of ascending coronal features observed near the Sun evolve as they move antisunward is obvious. The time-elongation profile of a transient tracked by HI can, moreover, be used to establish its angle out of the plane-of-the-sky; an illustration of such analysis reveals coronal mass ejection material that can be clearly observed propagating out to distances beyond 1AU. This work confirms the value of the time-elongation format in identifying/characterising transient activity in the inner heliosphere, whilst also validating the ability of HI to continuously monitor solar ejecta out to and beyond 1A
Positivity of Entropy in the Semi-Classical Theory of Black Holes and Radiation
Quantum stress-energy tensors of fields renormalized on a Schwarzschild
background violate the classical energy conditions near the black hole.
Nevertheless, the associated equilibrium thermodynamical entropy by
which such fields augment the usual black hole entropy is found to be positive.
More precisely, the derivative of with respect to radius, at fixed
black hole mass, is found to vanish at the horizon for {\it all} regular
renormalized stress-energy quantum tensors. For the cases of conformal scalar
fields and U(1) gauge fields, the corresponding second derivative is positive,
indicating that has a local minimum there. Explicit calculation
shows that indeed increases monotonically for increasing radius and
is positive. (The same conclusions hold for a massless spin 1/2 field, but the
accuracy of the stress-energy tensor we employ has not been confirmed, in
contrast to the scalar and vector cases). None of these results would hold if
the back-reaction of the radiation on the spacetime geometry were ignored;
consequently, one must regard as arising from both the radiation
fields and their effects on the gravitational field. The back-reaction, no
matter how "small",Comment: 19 pages, RevTe
On the feasibility of N2 fixation via a single-site FeI/FeIV cycle: Spectroscopic studies of FeI(N2)FeI, FeIV=N, and related species
The electronic properties of an unusually redox-rich iron system, [PhBPR 3]FeNx (where [PhBPR 3] is [PhB(CH2PR2)3]−), are explored by Mössbauer, EPR, magnetization, and density-functional methods to gain a detailed picture regarding their oxidation states and electronic structures. The complexes of primary interest in this article are the two terminal iron(IV) nitride species, [PhBPiPr 3]FeN (3a) and [PhBPCH2Cy 3]FeN (3b), and the formally diiron(I) bridged-Fe(μ-N2)Fe species, {[PhBPiPr 3]Fe}2(μ-N2) (4). Complex 4 is chemically related to 3a via a spontaneous nitride coupling reaction. The diamagnetic iron(IV) nitrides 3a and 3b exhibit unique electronic environments that are reflected in their unusual Mössbauer parameters, including quadrupole-splitting values of 6.01(1) mm/s and isomer shift values of −0.34(1) mm/s. The data for 4 suggest that this complex can be described by a weak ferromagnetic interaction (J/D < 1) between two iron(I) centers. For comparison, four other relevant complexes also are characterized: a diamagnetic iron(IV) trihydride [PhBPiPr 3]Fe(H)3(PMe3) (5), an S = 3/2 iron(I) phosphine adduct [PhBPiPr 3]FePMe3 (6), and the S = 2 iron(II) precursors to 3a, [PhBPiPr 3]FeCl and [PhBPiPr 3]Fe-2,3:5,6-dibenzo-7-aza bicyclo[2.2.1]hepta-2,5-diene (dbabh). The electronic properties of these respective complexes also have been explored by density-functional methods to help corroborate our spectral assignments and to probe their electronic structures further
High regulatory gene use in sea urchin embryogenesis: Implications for bilaterian development and evolution
A global scan of transcription factor usage in the sea urchin embryo was carried out in the context of the Strongylocentrotus purpuratus genome sequencing project, and results from six individual studies are here considered. Transcript prevalence data were obtained for over 280 regulatory genes encoding sequence-specific transcription factors of every known family, but excluding genes encoding zinc finger proteins. This is a statistically inclusive proxy for the total “regulome” of the sea urchin genome. Close to 80% of the regulome is expressed at significant levels by the late gastrula stage. Most regulatory genes must be used repeatedly for different functions as development progresses. An evolutionary implication is that animal complexity at the stage when the regulome first evolved was far simpler than even the last common bilaterian ancestor, and is thus of deep antiquity
The WFC3 Galactic Bulge Treasury Program: A First Look at Resolved Stellar Population Tools
[Abridged] When WFC3 is installed on HST, the community will have powerful
new tools for investigating resolved stellar populations. The WFC3 Galactic
Bulge Treasury program will obtain deep imaging on 4 low-extinction fields.
These non-proprietary data will enable a variety of science investigations not
possible with previous data sets. To aid in planning for the use of these data
and for future proposals, we provide an introduction to the program, its
photometric system, and the associated calibration effort.
The observing strategy is based upon a new 5-band photometric system spanning
the UV, optical, and near-infrared. With these broad bands, one can construct
reddening-free indices of Teff and [Fe/H]. Besides the 4 bulge fields, the
program will target 6 fields in well-studied star clusters, spanning a wide
range of [Fe/H]. The cluster data serve to calibrate the indices, provide
population templates, and correct the transformation of isochrones into the
WFC3 photometric system. The bulge data will shed light on the bulge formation
history, and will also serve as population templates for other studies. One of
the fields includes 12 candidate hosts of extrasolar planets.
CMDs are the most popular tool for analyzing resolved stellar populations.
However, due to degeneracies among Teff, [Fe/H], and reddening in traditional
CMDs, it can be difficult to draw robust conclusions from the data. The 5-band
system used for the bulge Treasury observations will provide indices that are
roughly orthogonal in Teff and [Fe/H], and we argue that model fitting in an
index-index diagram will make better use of the information than fitting
separate CMDs. We provide simulations to show the expected data quality and the
potential for differentiating between different star-formation histories.Comment: Accepted for publication in The Astronomical Journal. 9 pages, 8
figures, latex, AJ forma
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