169 research outputs found
Neutron optical test of completeness of quantum root-mean-square errors
One of the major problems in quantum physics has been to generalize the
classical root-mean-square error to quantum measurements to obtain an error
measure satisfying both soundness (to vanish for any accurate measurements) and
completeness (to vanish only for accurate measurements). A noise-operator based
error measure has been commonly used for this purpose, but it has turned out
incomplete. Recently, Ozawa proposed a new definition for a noise-operator
based error measure to be both sound and complete. Here, we present a neutron
optical demonstration for the completeness of the new error measure for both
projective (or sharp) as well as generalized (or unsharp) measurements.Comment: 7 pages, 4 figures and Supplementary Informatio
Circuit analysis of quantum measurement
We develop a circuit theory that enables us to analyze quantum measurements
on a two-level system and on a continuous-variable system on an equal footing.
As a measurement scheme applicable to both systems, we discuss a swapping state
measurement which exchanges quantum states between the system and the measuring
apparatus before the apparatus meter is read out. This swapping state
measurement has an advantage in gravitational-wave detection over contractive
state measurement in that the postmeasurement state of the system can be set to
a prescribed one, regardless of the outcome of the measurement.Comment: 11pages, 7figure
Experimental demonstration of a universally valid error-disturbance uncertainty relation in spin-measurements
The uncertainty principle generally prohibits determination of certain pairs
of quantum mechanical observables with arbitrary precision and forms the basis
of indeterminacy in quantum mechanics. It was Heisenberg who used the famous
gamma-ray microscope thought experiment to illustrate this indeterminacy. A
lower bound was set for the product of the measurement error of an observable
and the disturbance caused by the measurement. Later on, the uncertainty
relation was reformulated in terms of standard deviations, which focuses solely
on indeterminacy of predictions and neglects unavoidable recoil in measuring
devices. A correct formulation of the error-disturbance relation, taking recoil
into account, is essential for a deeper understanding of the uncertainty
principle. However, the validity of Heisenberg's original error-disturbance
uncertainty relation is justifed only under limited circumstances. Another
error-disturbance relation, derived by rigorous and general theoretical
treatments of quantum measurements, is supposed to be universally valid. Here,
we report a neutron optical experiment that records the error of a
spin-component measurement as well as the disturbance caused on another
spin-component measurement. The results confirm that both error and disturbance
completely obey the new, more general relation but violate the old one in a
wide range of an experimental parameter.Comment: 11 pages, 5 figures, Nature Physics (in press
Comprehensive Dipeptide Analysis Revealed Cancer-Specific Profile in the Liver of Patients with Hepatocellular Carcinoma and Hepatitis
As the physical properties and functionality of dipeptides differ from those of amino acids, they have attracted attention in metabolomics; however, their functions in vivo have not been clarified in detail. Hepatocellular carcinoma (HCC) is the most common type of primary liver cancer, and its major cause is chronic hepatitis. This study was conducted to explore tumor-specific dipeptide characteristics by performing comprehensive dipeptide analysis in the tumor and surrounding nontumor tissue of patients with HCC. Dipeptides were analyzed by liquid chromatography tandem mass spectrometry and capillary electrophoresis tandem mass spectrometry. Principal component analysis using 236 detected dipeptides showed differences in the dipeptide profiles between nontumor and tumor tissues; however, no clear difference was observed in etiological comparison. In addition, the N- and C-terminal amino acid compositions of the detected dipeptides significantly differed, suggesting the substrate specificity of enzyme proteins, such as peptidase. Furthermore, hepatitis-derived HCC may show a characteristic dipeptide profile even before tumor formation. These results provide insight into HCC pathogenesis and may help identify novel biomarkers for diagnosis
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