253 research outputs found
Digital quantum simulators in a scalable architecture of hybrid spin-photon qubits
Resolving quantum many-body problems represents one of the greatest
challenges in physics and physical chemistry, due to the prohibitively large
computational resources that would be required by using classical computers. A
solution has been foreseen by directly simulating the time evolution through
sequences of quantum gates applied to arrays of qubits, i.e. by implementing a
digital quantum simulator. Superconducting circuits and resonators are emerging
as an extremely-promising platform for quantum computation architectures, but a
digital quantum simulator proposal that is straightforwardly scalable,
universal, and realizable with state-of-the-art technology is presently
lacking. Here we propose a viable scheme to implement a universal quantum
simulator with hybrid spin-photon qubits in an array of superconducting
resonators, which is intrinsically scalable and allows for local control. As
representative examples we consider the transverse-field Ising model, a spin-1
Hamiltonian, and the two-dimensional Hubbard model; for these, we numerically
simulate the scheme by including the main sources of decoherence. In addition,
we show how to circumvent the potentially harmful effects of inhomogeneous
broadening of the spin systems
Constructing Clock-Transition-Based Two-Qubit Gates from Dimers of Molecular Nanomagnets
A good qubit must have a coherence time long enough for gate operations to be
performed. Avoided level crossings allow for clock transitions in which
coherence is enhanced by the insensitivity of the transition to fluctuations in
external fields. Because of this insensitivity, it is not obvious how to
effectively couple qubits together while retaining clock-transition behavior.
Here we present a scheme for using a heterodimer of two coupled molecular
nanomagnets, each with a clock transition at zero magnetic field, in which all
of the gate operations needed to implement one- and two-qubit gates can be
implemented with pulsed radio-frequency radiation. We show that given realistic
coupling strengths between the nanomagnets in the dimer, good gate fidelities
(99.4\%) can be achieved. We identify the primary sources of error in
implementing gates and discuss how these may be mitigated, and investigate the
range of coherence times necessary for such a system to be a viable platform
for implementing quantum computing protocols.Comment: Version accepted by Phys. Rev. Research. Fig. 1 has minor
modifications. References adde
Large, sustained cardiac lipid peroxidation and reduced antioxidant capacity in the coronary circulation after brief episodes of myocardial ischemia
AbstractOBJECTIVESWe sought to investigate whether a brief episode of myocardial ischemia produces a detectable cardiac oxidative stress in patients undergoing elective coronary angioplasty (PTCA).BACKGROUNDAlthough cardiac oxidative stress has been clearly demonstrated in experimental models of ischemia-reperfusion, its presence in patients after transient myocardial ischemia is still unclear.METHODSIn order to evaluate oxidative stress in ischemic cardiac regions, plasma conjugated dienes (CD), lipid hydroperoxides (ROOHs) and total antioxidant capacity (TRAP), independent indexes of oxidative stress, were measured in the aorta and great cardiac vein (GCV) before (t0), 1, (t1), 5 (t5) and 15 min (t15) after first balloon inflation in 15 patients undergoing PTCA on left anterior descending coronary artery (Group 1); six patients with right coronary artery stenosis (Group 2), which is not drained by the GCV, were studied as controls.RESULTSIn Group 1 at baseline, CD and ROOHs levels were higher in GCV than in aorta (p < 0.01 for both), and TRAP levels were lower (p < 0.01). Aortic levels of CD, ROOHs and TRAP did not change at any time after t0; venous levels of CD and ROOHs levels markedly increased at t1, at t5and remained elevated at t15(p < 0.01 for all comparisons vs. t0); venous levels of TRAP decreased at t1and t5(p < 0.01 vs. t0) and returned to normal at t15. In Group 2, CD, ROOHs and TRAP levels were similar in the aorta and GCV and did not change throughout the study.CONCLUSIONSShort episodes of myocardial ischemia during PTCA induce a sustained oxidative stress, which is detectable in the venous effluent of reperfused myocardium
Assessment of Parathyroid Function in Clinical Practice: Which Parathyroid Hormone Assay Is Better?
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Fatty acids and triacylglycerols profiles from sicilian (Cold pressed vs. soxhlet) grape seed oils
Among the Sicilian economic productive sectors, that of wine production has today a considerable economic value. However, with the growth of this sector, notable was the increase in the production of waste, which to date is not only an economic damage for companies, but also a threat to the environment. It is known that waste from wine production has properties (e.g., antioxidants) which have potential reuse at cosmetic, pharmaceutical and nutritional levels to obtain economically sustainable applications. A new goal is given by the recovery of added value compounds from agri-food wastes and by-products. Grape seed oil is a promising vegetable fat and cold pressing does not involve the use of chemicals, which are harmful to health. It implies that cold-pressed seed oils may contain phytochemicals, as well as natural antioxidants, more than refined oils. In this context, this works aims at studying the chemical characterization (triglycerides profile and composition in fatty acids) of grape seed oils obtained from Soxhlet and cold pressed extraction from Sicilian red grape seeds and white grape seeds. The possibility of obtaining high yields of triglycerides and fatty acids from the waste of wine production through new extraction methods would open up new perspectives for the reuse of waste in a human and animal food context. The results of this work allow the opening up of new perspectives to reuse and then reduce these wastes, helping not only to reduce the damage to the environment and costs for companies but also to create a new product that is environmentally sustainable and with an important economic value
Management of syncope: clinical and economic impact of a Syncope Unit
Aims Aim of this observational study is to evaluate the clinical performance of a Syncope Unit, in order to assess whether the implemented organization really improves syncope management. Methods and results The study enrolled patients with unexplained syncope who were consecutively referred to our Syncope Unit, either as outpatients or during hospitalization, in a 2-month period. The design of this observational study consists in three phases: a retrospective analysis of their clinical. management in the 9 months prior to the first attendance at the Syncope Unit (phase one), their subsequent clinical management in the Syncope Unit (phase two) and a 9-month follow-up (phase three). The retrospective analysis of phase one showed that 25% of patients had already been hospitalized without diagnosis. After Syncope Unit evaluation, diagnosis was obtained in 82% of patients, with 15% of patients indicated to pacing. In the follow-up, 23% of patients experienced a syncopal recurrence. Our analysis indicated an 85% reduction of hospital costs in the follow-up period. Conclusion The clinical and economic analysis of the three phases of our study demonstrates that a Syncope Unit allows an improved management of patients with syncope
Spin dynamics of molecular nanomagnets fully unraveled by four-dimensional inelastic neutron scattering
Molecular nanomagnets are among the first examples of spin systems of finite
size and have been test-beds for addressing a range of elusive but important
phenomena in quantum dynamics. In fact, for short-enough timescales the spin
wavefunctions evolve coherently according to the an appropriate cluster
spin-Hamiltonian, whose structure can be tailored at the synthetic level to
meet specific requirements. Unfortunately, to this point it has been impossible
to determine the spin dynamics directly. If the molecule is sufficiently
simple, the spin motion can be indirectly assessed by an approximate model
Hamiltonian fitted to experimental measurements of various types. Here we show
that recently-developed instrumentation yields the four-dimensional
inelastic-neutron scattering function S(Q,E) in vast portions of reciprocal
space and enables the spin dynamics to be determined with no need of any model
Hamiltonian. We exploit the Cr8 antiferromagnetic ring as a benchmark to
demonstrate the potential of this new approach. For the first time we extract a
model-free picture of the quantum dynamics of a molecular nanomagnet. This
allows us, for example, to examine how a quantum fluctuation propagates along
the ring and to directly test the degree of validity of the
N\'{e}el-vector-tunneling description of the spin dynamics
Cosmological Parameters from the 2003 flight of BOOMERANG
We present the cosmological parameters from the CMB intensity and
polarization power spectra of the 2003 Antarctic flight of the BOOMERANG
telescope. The BOOMERANG data alone constrains the parameters of the
CDM model remarkably well and is consistent with constraints from a
multi-experiment combined CMB data set. We add LSS data from the 2dF and SDSS
redshift surveys to the combined CMB data set and test several extensions to
the standard model including: running of the spectral index, curvature, tensor
modes, the effect of massive neutrinos, and an effective equation of state for
dark energy. We also include an analysis of constraints to a model which allows
a CDM isocurvature admixture.Comment: 18 pages, 10 figures, submitted to Ap
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