425 research outputs found
Quantum Reed-Solomon Codes
After a brief introduction to both quantum computation and quantum error
correction, we show how to construct quantum error-correcting codes based on
classical BCH codes. With these codes, decoding can exploit additional
information about the position of errors. This error model - the quantum
erasure channel - is discussed. Finally, parameters of quantum BCH codes are
provided.Comment: Summary only (2 pages), for the full version see: Proceedings Applied
Algebra, Algebraic Algorithms and Error-Correcting Codes (AAECC-13), Lecture
Notes in Computer Science 1719, Springer, 199
Anti-series varactor network with improved linearity performances in the presence of inductive and capacitive parasitics
ABSTRACT: This paper proposes a varactor-based circuit technique intended for amplitude and phase control, with improved linearity in the presence of parasitic capacitances and parasitic inductances. The mechanism causing linearity degradation in an anti-series varactor network that includes significant parasitic elements - a key aspect that, to our knowledge, has never been reported - is first studied using an analytical approach based on multi-tone excitation. It is demonstrated that simply optimizing the ratio of diode sizes is insufficient to circumvent this linearity degradation. The underlying linearity degradation concept serves as the basis for the introduction of a modified anti-series controllable capacitance, followed by a design and practical implementation. Experimental validations with multi-tone and modulated signals demonstrate improved linearity performances with respect to the state-of-the-art when parasitic capacitances and inductances are significant. Moreover, it is shown that the complete varactor-based circuit topology proposed here, which uses the proposed modified anti-series controllable capacitance in conjunction with a second-harmonic trap filter, constitutes a very attractive alternative to the state-of-the-art anti-series/anti-parallel topology, since it reduces the required number of diodes by a factor of 2. Measurements on discrete-component designs operating at 3.6GHz, hence with significant parasitic effects, demonstrate that the proposed circuit topology improves the 3 rd order intermodulation distortion levels by 10.6dB and 6.6dB at output powers of 10dBm and 18dBm respectively, in comparison with the state-of-the-art topology. Measurements with a 16QAM modulated signal also show 3.9dB improvement in ACPR at 18dBm. These performances constitute improved state-of-the-art results in anti-series hyper-abrupt varactor-based electronic control
Perfect quantum error correction coding in 24 laser pulses
An efficient coding circuit is given for the perfect quantum error correction
of a single qubit against arbitrary 1-qubit errors within a 5 qubit code. The
circuit presented employs a double `classical' code, i.e., one for bit flips
and one for phase shifts. An implementation of this coding circuit on an
ion-trap quantum computer is described that requires 26 laser pulses. A further
circuit is presented requiring only 24 laser pulses, making it an efficient
protection scheme against arbitrary 1-qubit errors. In addition, the
performance of two error correction schemes, one based on the quantum Zeno
effect and the other using standard methods, is compared. The quantum Zeno
error correction scheme is found to fail completely for a model of noise based
on phase-diffusion.Comment: Replacement paper: Lost two laser pulses gained one author; added
appendix with circuits easily implementable on an ion-trap compute
The Myxoma Poxvirus Protein, M11L, Prevents Apoptosis by Direct Interaction with the Mitochondrial Permeability Transition Pore
M11L, an antiapoptotic protein essential for the virulence of the myxoma poxvirus, is targeted to mitochondria and prevents the loss of mitochondrial membrane potential that accompanies cell death. In this study we show, using a cross-linking approach, that M11L physically associates with the mitochondrial peripheral benzodiazepine receptor (PBR) component of the permeability transition (PT) pore. Close association of M11L and the PBR is also indicated by fluorescence resonance energy transfer (FRET) analysis. Stable expression of M11L prevents the release of mitochondrial cytochrome c induced by staurosporine or protoporphyrin IX (PPIX), a ligand of the PBR. Transiently expressed M11L also prevents mitochondrial membrane potential loss induced by PPIX, or induced by staurosporine in combination with PK11195, another ligand of the PBR. Myxoma virus infection and the associated expression of early proteins, including M11L, protects cells from staurosporine- and Fas-mediated mitochondrial membrane potential loss and this effect is augmented by the presence of PBR. We conclude that M11L regulates the mitochondrial permeability transition pore complex, most likely by direct modulation of the PBR
Identification of dichloroacetic acid degrading Cupriavidus bacteria in a drinking water distribution network model
Aims: Bacterial community structure and composition of a drinking water
network were assessed to better understand this ecosystem in relation to
haloacetic acid (HAA) degradation and to identify new bacterial species having
HAA degradation capacities.
Methods and Results: Biofilm samples were collected from a model system,
simulating the end of the drinking water distribution network and supplied
with different concentrations of dichloroacetic and trichloroacetic acids at
different periods over the course of a year. The samples were analysed by
culturing, denaturing gradient gel electrophoresis (DGGE) and sequencing.
Pipe diameter and HAA ratios did not impact the bacterial community
profiles, but the season had a clear influence. Based on DGGE profiles, it
appeared that a particular biomass has developed during the summer
compared with the other seasons. Among the bacteria isolated in this study,
those from genus Cupriavidus were able to degrade dichloroacetic acid.
Moreover, these bacteria degrade dichloroacetic acid at 18°C but not at 10°C.
Conclusions: The microbial diversity evolved throughout the experiment, but
the bacterial community was distinct during the summer. Results obtained on
the capacity of Cupriavidus to degrade DCAA only at 18°C but not at 10°C
indicate that water temperature is a major element affecting DCAA
degradation and confirming observations made regarding season influence on
HAA degradation in the drinking water distribution network.
Significance and Impact of the Study: This is the first demonstration of the
HAA biodegradation capacity of the genus Cupriavidu
Two-Bit Gates are Universal for Quantum Computation
A proof is given, which relies on the commutator algebra of the unitary Lie
groups, that quantum gates operating on just two bits at a time are sufficient
to construct a general quantum circuit. The best previous result had shown the
universality of three-bit gates, by analogy to the universality of the Toffoli
three-bit gate of classical reversible computing. Two-bit quantum gates may be
implemented by magnetic resonance operations applied to a pair of electronic or
nuclear spins. A ``gearbox quantum computer'' proposed here, based on the
principles of atomic force microscopy, would permit the operation of such
two-bit gates in a physical system with very long phase breaking (i.e., quantum
phase coherence) times. Simpler versions of the gearbox computer could be used
to do experiments on Einstein-Podolsky-Rosen states and related entangled
quantum states.Comment: 21 pages, REVTeX 3.0, two .ps figures available from author upon
reques
Entropy and Quantum Kolmogorov Complexity: A Quantum Brudno's Theorem
In classical information theory, entropy rate and Kolmogorov complexity per
symbol are related by a theorem of Brudno. In this paper, we prove a quantum
version of this theorem, connecting the von Neumann entropy rate and two
notions of quantum Kolmogorov complexity, both based on the shortest qubit
descriptions of qubit strings that, run by a universal quantum Turing machine,
reproduce them as outputs.Comment: 26 pages, no figures. Reference to publication added: published in
the Communications in Mathematical Physics
(http://www.springerlink.com/content/1432-0916/
Extreme Ultraviolet Variability Experiment (EVE) on the Solar Dynamics Observatory (SDO): Overview of Science Objectives, Instrument Design, Data Products, and Model Developments
The highly variable solar extreme ultraviolet (EUV) radiation is the major energy input to the Earth’s upper atmosphere, strongly impacting the geospace environment, affecting satellite operations, communications, and navigation. The Extreme ultraviolet Variability Experiment (EVE) onboard the NASA Solar Dynamics Observatory (SDO) will measure the solar EUV irradiance from 0.1 to 105 nm with unprecedented spectral resolution (0.1 nm), temporal cadence (ten seconds), and accuracy (20%). EVE includes several irradiance instruments: The Multiple EUV Grating Spectrographs (MEGS)-A is a grazing-incidence spectrograph that measures the solar EUV irradiance in the 5 to 37 nm range with 0.1-nm resolution, and the MEGS-B is a normal-incidence, dual-pass spectrograph that measures the solar EUV irradiance in the 35 to 105 nm range with 0.1-nm resolution. To provide MEGS in-flight calibration, the EUV SpectroPhotometer (ESP) measures the solar EUV irradiance in broadbands between 0.1 and 39 nm, and a MEGS-Photometer measures the Sun’s bright hydrogen emission at 121.6 nm. The EVE data products include a near real-time space-weather product (Level 0C), which provides the solar EUV irradiance in specific bands and also spectra in 0.1-nm intervals with a cadence of one minute and with a time delay of less than 15 minutes. The EVE higher-level products are Level 2 with the solar EUV irradiance at higher time cadence (0.25 seconds for photometers and ten seconds for spectrographs) and Level 3 with averages of the solar irradiance over a day and over each one-hour period. The EVE team also plans to advance existing models of solar EUV irradiance and to operationally use the EVE measurements in models of Earth’s ionosphere and thermosphere. Improved understanding of the evolution of solar flares and extending the various models to incorporate solar flare events are high priorities for the EVE team.United States. National Aeronautics and Space Administration (contract NAS5-02140
New VLA observations of the SNR Puppis A: the radio properties and the correlatoin withe the X-ray emission
In this paper we report on a new study of the SNR Puppis A based on VLA
observations at 1425 MHz; the improvement represents a factor of two in angular
resolution and almost ten times in sensitivity compared to the best previous
image of Puppis A. This new image is used to compare with re-processed 327 MHz
data and ROSAT and Chandra images to investigate morphological and spectral
characteristics.Comment: 14 pages, 9 figures, accepted for publication in A &
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