2,780 research outputs found
Conditional quantum-state transformation at a beam splitter
Using conditional measurement on a beam splitter, we study the transformation
of the quantum state of the signal mode within the concept of two-port
non-unitary transformation. Allowing for arbitrary quantum states of both the
input reference mode and the output reference mode on which the measurement is
performed, we show that the non-unitary transformation operator can be given as
an -ordered operator product, where the value of is entirely determined
by the absolute value of the beam splitter reflectance (or transmittance). The
formalism generalizes previously obtained results that can be recovered by
simple specification of the non-unitary transformation operator. As an
application, we consider the generation of Schr\"odinger-cat-like states. An
extension to mixed states and imperfect detection is outlined.Comment: 7 Postscript figures, using Late
Coherent Superposition States as Quantum Rulers
We explore the sensitivity of an interferometer based on a quantum circuit
for coherent states. We show that its sensitivity is at the Heisenberg limit.
Moreover we show that this arrangement can measure very small length intervals
Bridging the gap between policy and science in assessing the health status of marine ecosystems
Human activities, both established and emerging, increasingly affect the provision of marine ecosystem services that deliver societal and economic benefits. Monitoring the status of marine ecosystems and determining how human activities change their capacity to sustain benefits for society requires an evidence-based Integrated Ecosystem Assessment approach that incorporates knowledge of ecosystem functioning and services). Although, there are diverse methods to assess the status of individual ecosystem components, none assesses the health of marine ecosystems holistically, integrating information from multiple ecosystem components. Similarly, while acknowledging the availability of several methods to measure single pressures and assess their impacts, evaluation of cumulative effects of multiple pressures remains scarce. Therefore, an integrative assessment requires us to first understand the response of marine ecosystems to human activities and their pressures and then develop innovative, cost-effective monitoring tools that enable collection of data to assess the health status of large marine areas. Conceptually, combining this knowledge of effective monitoring methods with cost-benefit analyses will help identify appropriate management measures to improve environmental status economically and efficiently. The European project DEVOTES (DEVelopment Of innovative Tools for understanding marine biodiversity and assessing good Environmental Status) specifically addressed t hese topics in order to support policy makers and managers in implementing the European Marine Strategy Framework Directive. Here, we synthesize our main innovative findings, placing these within the context of recent wider research, and identifying gaps and the major future challenges
Macroscopically distinct quantum superposition states as a bosonic code for amplitude damping
We show how macroscopically distinct quantum superposition states
(Schroedinger cat states) may be used as logical qubit encodings for the
correction of spontaneous emission errors. Spontaneous emission causes a bit
flip error which is easily corrected by a standard error correction circuit.
The method works arbitrarily well as the distance between the amplitudes of the
superposed coherent states increases.Comment: 4 pages, 2 postscript figures, LaTeX2e, RevTeX, minor changes, 1
reference adde
Autofeedback scheme for preservation of macroscopic coherence in microwave cavities
We present a scheme for controlling the decoherence of a linear superposition
of two coherent states with opposite phases in a high-Q microwave cavity, based
on the injection of appropriately prepared ``probe'' and ``feedback'' Rydberg
atoms, improving the one presented in [D. Vitali et al., Phys. Rev. Lett. 79,
2442 (1997)]. In the present scheme, the information transmission from the
probe to the feedback atom is directly mediated by a second auxiliary cavity.
The detection efficiency for the probe atom is no longer a critical parameter,
and the decoherence time of the superposition state can be significantly
increased using presently available technology.Comment: revtex, 15 pages, 4 eps figure
Synthesis and characterization of entangled mesoscopic superpositions for a trapped electron
We propose a scheme for the generation and reconstruction of entangled states
between the internal and external (motional) degrees of freedom of a trapped
electron. Such states also exhibit quantum coherence at a mesoscopic level.Comment: 4 pages, 1 figure, RevTeX (twocolumn
Kondo Temperature for the Two-Channel Kondo Models of Tunneling Centers
The possibility for a two-channel Kondo () non Fermi liquid state to
appear in a metal as a result of the interaction between electrons and movable
structural defects is revisited. As usual, the defect is modeled by a heavy
particle moving in an almost symmetric double-well potential (DWP). Taking into
account only the two lowest states in DWP is known to lead to a Kondo-like
Hamiltonian with rather low Kondo temperature, . We prove that, in
contrast to previous believes, the contribution of higher excited states in DWP
does not enhance . On the contrary, is reduced by three orders of
magnitude as compared with the two-level model: the prefactor in is
determined by the spacing between the second and the third levels in DWP rather
than by the electron Fermi energy. Moreover, , turns out to be
parametrically smaller than the splitting between the two lowest levels.
Therefore, there is no microscopic model of movable defects which may justify
non-Fermi liquid phenomenology.Comment: 5 pages, 4 .eps figure
Exciton entanglement in two coupled semiconductor microcrystallites
Entanglement of the excitonic states in the system of two coupled
semiconductor microcrystallites, whose sizes are much larger than the Bohr
radius of exciton in bulk semiconductor but smaller than the relevant optical
wavelength, is quantified in terms of the entropy of entanglement. It is
observed that the nonlinear interaction between excitons increases the maximum
values of the entropy of the entanglement more than that of the linear coupling
model. Therefore, a system of two coupled microcrystallites can be used as a
good source of entanglement with fixed exciton number. The relationship between
the entropy of the entanglement and the population imbalance of two
microcrystallites is numerically shown and the uppermost envelope function for
them is estimated by applying the Jaynes principle.Comment: 16 pages, 6 figure
Zonal pressure gradient along the equatorial Atlantic
For three consecutive periods during the summer of 1974, ships of many nations made observations along the Atlantic equator as part of the GATE program [GARP (Global Atmospheric Research Program) Atlantic Tropical Experiment]. Combining these observations, it is found that the zonal pressure gradient over the central Atlantic at the surface and at 50 dbar, relative to 500 dbar, increased from 3.2 to 7.3 and 2.2 to 5.3 × 10-5 dynes/g respectively between June/July and August and then held close to the high values in September...
Survey of the quality of experimental design, statistical analysis and reporting of research using animals
For scientific, ethical and economic reasons, experiments involving animals should be appropriately designed, correctly analysed and transparently reported. This increases the scientific validity of the results, and maximises the knowledge gained from each experiment. A minimum amount of relevant information must be included in scientific publications to ensure that the methods and results of a study can be reviewed, analysed and repeated. Omitting essential information can raise scientific and ethical concerns. We report the findings of a systematic survey of reporting, experimental design and statistical analysis in published biomedical research using laboratory animals. Medline and EMBASE were searched for studies reporting research on live rats, mice and non-human primates carried out in UK and US publicly funded research establishments. Detailed information was collected from 271 publications, about the objective or hypothesis of the study, the number, sex, age and/or weight of animals used, and experimental and statistical methods. Only 59% of the studies stated the hypothesis or objective of the study and the number and characteristics of the animals used. Appropriate and efficient experimental design is a critical component of high-quality science. Most of the papers surveyed did not use randomisation (87%) or blinding (86%), to reduce bias in animal selection and outcome assessment. Only 70% of the publications that used statistical methods described their methods and presented the results with a measure of error or variability. This survey has identified a number of issues that need to be addressed in order to improve experimental design and reporting in publications describing research using animals. Scientific publication is a powerful and important source of information; the authors of scientific publications therefore have a responsibility to describe their methods and results comprehensively, accurately and transparently, and peer reviewers and journal editors share the responsibility to ensure that published studies fulfil these criteria
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