1,297 research outputs found
Emergence of a measurement basis in atom-photon scattering
The process of quantum measurement has been a long standing source of debate.
A measurement is postulated to collapse a wavefunction onto one of the states
of a predetermined set - the measurement basis. This basis origin is not
specified within quantum mechanics. According to the theory of decohernce, a
measurement basis is singled out by the nature of coupling of a quantum system
to its environment. Here we show how a measurement basis emerges in the
evolution of the electronic spin of a single trapped atomic ion due to
spontaneous photon scattering. Using quantum process tomography we visualize
the projection of all spin directions, onto this basis, as a photon is
scattered. These basis spin states are found to be aligned with the scattered
photon propagation direction. In accordance with decohernce theory, they are
subjected to a minimal increase in entropy due to the photon scattering, while,
orthogonal states become fully mixed and their entropy is maximally increased.
Moreover, we show that detection of the scattered photon polarization measures
the spin state of the ion, in the emerging basis, with high fidelity. Lastly,
we show that while photon scattering entangles all superpositions of pointer
states with the scattered photon polarization, the measurement-basis states
themselves remain classically correlated with it. Our findings show that photon
scattering by atomic spin superpositions fulfils all the requirements from a
quantum measurement process
High-fidelity state detection and tomography of a single ion Zeeman qubit
We demonstrate high-fidelity Zeeman qubit state detection in a single trapped
88 Sr+ ion. Qubit readout is performed by shelving one of the qubit states to a
metastable level using a narrow linewidth diode laser at 674 nm followed by
state-selective fluorescence detection. The average fidelity reached for the
readout of the qubit state is 0.9989(1). We then measure the fidelity of state
tomography, averaged over all possible single-qubit states, which is 0.9979(2).
We also fully characterize the detection process using quantum process
tomography. This readout fidelity is compatible with recent estimates of the
detection error-threshold required for fault-tolerant computation, whereas
high-fidelity state tomography opens the way for high-precision quantum process
tomography
Proteasome Lid Bridges Mitochondrial Stress with Cdc53/Cullin1 NEDDylation Status
Cycles of Cdc53/Cullin1 rubylation (a.k.a NEDDylation) protect ubiquitin-E3 SCF (Skp1-Cullin1-F-box protein) complexes from self-destruction and play an important role in mediating the ubiquitination of key protein substrates involved in cell cycle progression, development, and survival. Cul1 rubylation is balanced by the COP9 signalosome (CSN), a multi-subunit derubylase that shows 1:1 paralogy to the 26 S proteasome lid. The turnover of SCF substrates and their relevance to various diseases is well studied, yet, the extent by which environmental perturbations influence Cul1 rubylation/derubylation cycles per se is still unclear. In this study, we show that the level of cellular oxidation serves as a molecular switch, determining Cullin1 rubylation/derubylation ratio. We describe a mutant of the proteasome lid subunit, Rpn11 that exhibits accumulated levels of Cullin1-Rub1 conjugates, a characteristic phenotype of csn mutants. By dissecting between distinct phenotypes of rpn11 mutants, proteasome and mitochondria dysfunction, we were able to recognize the high reactive oxygen species (ROS) production during the transition of cells into mitochondrial respiration, as a checkpoint of Cullin1 rubylation in a reversible manner. Thus, the study adds the rubylation cascade to the list of cellular pathways regulated by redox homeostasis
How to Choose a Champion
League competition is investigated using random processes and scaling
techniques. In our model, a weak team can upset a strong team with a fixed
probability. Teams play an equal number of head-to-head matches and the team
with the largest number of wins is declared to be the champion. The total
number of games needed for the best team to win the championship with high
certainty, T, grows as the cube of the number of teams, N, i.e., T ~ N^3. This
number can be substantially reduced using preliminary rounds where teams play a
small number of games and subsequently, only the top teams advance to the next
round. When there are k rounds, the total number of games needed for the best
team to emerge as champion, T_k, scales as follows, T_k ~N^(\gamma_k) with
gamma_k=1/[1-(2/3)^(k+1)]. For example, gamma_k=9/5,27/19,81/65 for k=1,2,3.
These results suggest an algorithm for how to infer the best team using a
schedule that is linear in N. We conclude that league format is an ineffective
method of determining the best team, and that sequential elimination from the
bottom up is fair and efficient.Comment: 6 pages, 3 figure
Quantum control of Sr in a miniature linear Paul trap
We report on the construction and characterization of an apparatus for
quantum information experiments using Sr ions. A miniature linear
radio-frequency (rf) Paul trap was designed and built. Trap frequencies above 1
MHz in all directions are obtained with 50 V on the trap end-caps and less than
1 W of rf power. We encode a quantum bit (qubit) in the two spin states of the
electronic ground-state of the ion. We constructed all the necessary
laser sources for laser cooling and full coherent manipulation of the ions'
external and internal states. Oscillating magnetic fields are used for coherent
spin rotations. High-fidelity readout as well as a coherence time of 2.5 ms are
demonstrated. Following resolved sideband cooling the average axial vibrational
quanta of a single trapped ion is and a heating rate of
ms is measured.Comment: 8 pages,9 figure
Dynamics of tournaments: the soccer case
A random walk-like model is considered to discuss statistical aspects of
tournaments. The model is applied to soccer leagues with emphasis on the
scores. This competitive system was computationally simulated and the results
are compared with empirical data from the English, the German and the Spanish
leagues and showed a good agreement with them. The present approach enabled us
to characterize a diffusion where the scores are not normally distributed,
having a short and asymmetric tail extending towards more positive values. We
argue that this non-Gaussian behavior is related with the difference between
the teams and with the asymmetry of the scores system. In addition, we compared
two tournament systems: the all-play-all and the elimination tournaments.Comment: To appear in EPJ
Converting genetic network oscillations into somite spatial pattern
In most vertebrate species, the body axis is generated by the formation of
repeated transient structures called somites. This spatial periodicity in
somitogenesis has been related to the temporally sustained oscillations in
certain mRNAs and their associated gene products in the cells forming the
presomatic mesoderm. The mechanism underlying these oscillations have been
identified as due to the delays involved in the synthesis of mRNA and
translation into protein molecules [J. Lewis, Current Biol. {\bf 13}, 1398
(2003)]. In addition, in the zebrafish embryo intercellular Notch signalling
couples these oscillators and a longitudinal positional information signal in
the form of an Fgf8 gradient exists that could be used to transform these
coupled temporal oscillations into the observed spatial periodicity of somites.
Here we consider a simple model based on this known biology and study its
consequences for somitogenesis. Comparison is made with the known properties of
somite formation in the zebrafish embryo . We also study the effects of
localized Fgf8 perturbations on somite patterning.Comment: 7 pages, 7 figure
Communicable Ulcerative Colitis Induced by T-bet Deficiency in the Innate Immune System
Inflammatory bowel disease (IBD) has been attributed to overexuberant host immunity or the emergence of harmful intestinal flora. The transcription factor T-bet orchestrates inflammatory genetic programs in both adaptive and innate immunity. We describe a profound and unexpected function for T-bet in influencing the behavior of host inflammatory activity and commensal bacteria. T-bet deficiency in the innate immune system results in spontaneous and communicable ulcerative colitis in the absence of adaptive immunity and increased susceptibility to colitis in immunologically intact hosts. T-bet controls the response of the mucosal immune system to commensal bacteria by regulating TNF-α production in colonic dendritic cells, critical for colonic epithelial barrier maintenance. Loss of T-bet influences bacterial populations to become colitogenic, and this colitis is communicable to genetically intact hosts. These findings reveal a novel function for T-bet as a peacekeeper of host-commensal relationships and provide new perspectives on the pathophysiology of IBD
Fusion versus Breakup: Observation of Large Fusion Suppression for ^9Be + ^{208}Pb
Complete fusion excitation functions for Be + Pb have been
measured to high precision at near barrier energies. The experimental fusion
barrier distribution extracted from these data allows reliable prediction of
the expected complete fusion cross-sections. However, the measured
cross-sections are only 68% of those predicted. The large cross-sections
observed for incomplete fusion products support the interpretation that this
suppression of fusion is caused by Be breaking up into charged fragments
before reaching the fusion barrier. Implications for the fusion of radioactive
nuclei are discussed.Comment: RevTex, 11 pages, 2 postscript figures, to appear in PR
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