181 research outputs found
Nuclear Magnetic Resonance Quantum Computing Using Liquid Crystal Solvents
Liquid crystals offer several advantages as solvents for molecules used for
nuclear magnetic resonance quantum computing (NMRQC). The dipolar coupling
between nuclear spins manifest in the NMR spectra of molecules oriented by a
liquid crystal permits a significant increase in clock frequency, while short
spin-lattice relaxation times permit fast recycling of algorithms, and save
time in calibration and signal-enhancement experiments. Furthermore, the use of
liquid crystal solvents offers scalability in the form of an expanded library
of spin-bearing molecules suitable for NMRQC. These ideas are demonstrated with
the successful execution of a 2-qubit Grover search using a molecule
(CHCl) oriented in a liquid crystal and a clock speed eight
times greater than in an isotropic solvent. Perhaps more importantly, five
times as many logic operations can be executed within the coherence time using
the liquid crystal solvent.Comment: Minor changes. Published in Appl. Phys. Lett. v.75, no.22, 29 Nov
1999, p.3563-356
Non-thermal nuclear magnetic resonance quantum computing using hyperpolarized Xenon
Current experiments in liquid-state nuclear magnetic resonance quantum
computing are limited by low initial polarization. To address this problem, we
have investigated the use of optical pumping techniques to enhance the
polarization of a 2-qubit NMR quantum computer (13C and 1H in 13CHCl3). To
efficiently use the increased polarization, we have generalized the procedure
for effective pure state preparation. With this new, more flexible scheme, an
effective pure state was prepared with polarization-enhancement of a factor of
10 compared to the thermal state. An implementation of Grover's quantum search
algorithm was demonstrated using this new technique.Comment: 4 pages, 3 figures. Submitted for publicatio
Implementation of a three-quantum-bit search algorithm
We report the experimental implementation of Grover's quantum search
algorithm on a quantum computer with three quantum bits. The computer consists
of molecules of C-labeled CHFBr, in which the three weakly coupled
spin-1/2 nuclei behave as the bits and are initialized, manipulated, and read
out using magnetic resonance techniques. This quantum computation is made
possible by the introduction of two techniques which significantly reduce the
complexity of the experiment and by the surprising degree of cancellation of
systematic errors which have previously limited the total possible number of
quantum gates.Comment: Published in Applied Physics Letters, vol. 76, no. 5, 31 January
2000, p.646-648, after minor revisions. (revtex, mypsfig2.sty, 3 figures
Sulfur and Hydrogen Isotope Anomalies in Meteorite Sulfonic Acids
Intramolecular carbon, hydrogen, and sulfur isotope ratios were measured on a homologous series of organic sulfonic acids discovered in the Murchison meteorite. Mass-independent sulfur isotope fractionations were observed along with high deuterium/hydrogen ratios. The deuterium enrichments indicate formation of the hydrocarbon portion of these compounds in a low-temperature environment that is consistent with that of interstellar clouds. Sulfur-33 enrichments observed in methanesulfonic acid could have resulted from gas-phase ultraviolet irradiation of a precursor, carbon disulfide. The source of the sulfonic acid precursors may have been the reactive interstellar molecule carbon monosulfide
Magnetic resonance investigation into the mechanisms involved in the development of high-altitude cerebral edema
Rapid ascent to high altitude commonly results in acute mountain sickness, and on occasion potentially fatal high-altitude cerebral edema. The exact pathophysiological mechanisms behind these syndromes remain to be determined. We report a study in which 12 subjects were exposed to a FiO2 = 0.12 for 22 h and underwent serial magnetic resonance imaging sequences to enable measurement of middle cerebral artery velocity, flow and diameter, and brain parenchymal, cerebrospinal fluid and cerebral venous volumes. Ten subjects completed 22 h and most developed symptoms of acute mountain sickness (mean Lake Louise Score 5.4; p < 0.001 vs. baseline). Cerebral oxygen delivery was maintained by an increase in middle cerebral artery velocity and diameter (first 6 h). There appeared to be venocompression at the level of the small, deep cerebral veins (116 cm3 at 2 h to 97 cm3 at 22 h; p < 0.05). Brain white matter volume increased over the 22-h period (574 ml to 587 ml; p < 0.001) and correlated with cumulative Lake Louise scores at 22 h (p < 0.05). We conclude that cerebral oxygen delivery was maintained by increased arterial inflow and this preceded the development of cerebral edema. Venous outflow restriction appeared to play a contributory role in the formation of cerebral edema, a novel feature that has not been observed previously
Experimental Realization of A Two Bit Phase Damping Quantum Code
Using nuclear magnetic resonance techniques, we experimentally investigated
the effects of applying a two bit phase error detection code to preserve
quantum information in nuclear spin systems. Input states were stored with and
without coding, and the resulting output states were compared with the
originals and with each other. The theoretically expected result, net reduction
of distortion and conditional error probabilities to second order, was indeed
observed, despite imperfect coding operations which increased the error
probabilities by approximately 5%. Systematic study of the deviations from the
ideal behavior provided quantitative measures of different sources of error,
and good agreement was found with a numerical model. Theoretical questions in
quantum error correction in bulk nuclear spin systems including fidelity
measures, signal strength and syndrome measurements are discussed.Comment: 21 pages, 17 figures, mypsfig2, revtex. Minor changes made to appear
in PR
Realization of logically labeled effective pure states for bulk quantum computation
We report the first use of "logical labeling" to perform a quantum
computation with a room-temperature bulk system. This method entails the
selection of a subsystem which behaves as if it were at zero temperature -
except for a decrease in signal strength - conditioned upon the state of the
remaining system. No averaging over differently prepared molecules is required.
In order to test this concept, we execute a quantum search algorithm in a
subspace of two nuclear spins, labeled by a third spin, using solution nuclear
magnetic resonance (NMR), and employing a novel choice of reference frame to
uncouple nuclei.Comment: PRL 83, 3085 (1999). Small changes made to improve readability and
remove ambiguitie
Renal failure and leukocytosis are predictors of a complicated course of clostridium difficile infection if measured on day of diagnosis
Nonsevere Clostridium difficile infection (CDI) and severe CDI, which carries a higher risk than nonsevere CDI for treatment failure and CDI recurrence, are difficult to distinguish at the time of diagnosis. To investigate the prognostic value of 3 markers of severe CDI suggested by recent guidelines (fever, leukocytosis, and renal failure), we used the database of 2 randomized controlled trials, which contained information for 1105 patients with CDI. Leukocytosis (risk ratio [RR], 2.29; 95% confidence interval [CI], 1.63–3.21) and renal failure (RR, 2.52; 95% CI, 1.82–3.50) were associated with treatment failure. Fever, although associated with treatment failure (RR, 2.45; 95% CI, 1.07–5.61), was rare. Renal failure was the only significant predictor of recurrence (RR, 1.45; 95% CI, 1.05–2.02). Different timing of measurements of leukocyte count and serum creatinine level around the CDI diagnosis led to a different severity classification in many cases. In conclusion, both leukocytosis and renal failure are useful predictors, although timing of measurement is important
Both RyRs and TPCs are required for NAADP-induced intracellular Ca2+ release
Intracellular Ca2+ release is mostly mediated by inositol trisphosphate, but intracellular cyclic-ADP-ribose (cADPR) and nicotinic acid adenine dinucleotide phosphate (NAADP) are important messengers in many systems. Whereas cADPR generally activates type 2 ryanodine receptors (RyR2s), the NAADP-activated Ca2+ release mechanism is less clear. Using knockouts and antibodies against RyRs and Two-Pore Channels (TPCs), we have compared their relative importance for NAADP-induced Ca2+ release from two-photon permeabilized pancreatic acinar cells. In these cells, cholecystokinin-elicited Ca2+ release is mediated by NAADP. TPC2-KO reduced NAADP-induced Ca2+ release by 64%, but the combination of TPC2-KO and an antibody against TPC1, significantly reduced Ca2+ release by 86% (64% vs. 86%, p TPC2 > RyR3 > TPC1 >> RyR2. However, when assessing NAADP-induced Ca2+ release solely from the acidic stores (granules/endosomes/lysosomes), antibodies against TPC2 and TPC1 virtually abolished the Ca2+ liberation as did antibodies against RyR1 and RyR3. Our results indicate that the primary, but very small, NAADP-elicited Ca2+ release via TPCs from endosomes/lysosomes triggers the detectable Ca2+-induced Ca2+ release via RyR1 and RyR3 occurring from the granules and the ER
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