488 research outputs found
Toward Spin Squeezing with Trapped Ions
Building robust instruments capable of making interferometric measurements
with precision beyond the standard quantum limit remains an important goal in
many metrology laboratories. We describe here the basic concepts underlying
spin squeezing experiments that allow one to surpass this limit. In priniciple
it is possible to reach the so-called Heisenberg limit, which constitutes an
improvement in precision by a factor , where is the number of
particles on which the measurement is carried out. In particular, we focus on
recent progress toward implementing spin squeezing with a cloud of beryllium
ions in a Penning ion trap, via the geometric phase gate used more commonly for
performing two-qubit entangling operations in quantum computing experiments.Comment: 18 pages, 9 figures, Contribution to Quantum Africa 2010 conference
proceeding
High-order noise filtering in nontrivial quantum logic gates
Treating the effects of a time-dependent classical dephasing environment
during quantum logic operations poses a theoretical challenge, as the
application of non-commuting control operations gives rise to both dephasing
and depolarization errors that must be accounted for in order to understand
total average error rates. We develop a treatment based on effective
Hamiltonian theory that allows us to efficiently model the effect of classical
noise on nontrivial single-bit quantum logic operations composed of arbitrary
control sequences. We present a general method to calculate the
ensemble-averaged entanglement fidelity to arbitrary order in terms of noise
filter functions, and provide explicit expressions to fourth order in the noise
strength. In the weak noise limit we derive explicit filter functions for a
broad class of piecewise-constant control sequences, and use them to study the
performance of dynamically corrected gates, yielding good agreement with
brute-force numerics.Comment: Revised and expanded to include filter function terms beyond first
order in the Magnus expansion. Related manuscripts available from
http://www.physics.usyd.edu.au/~mbiercu
A clinical delineation of tachyphemia (cluttering)
Cluttering constitutes one of the most important disorders of speech, language and communication in general. The majority of c1utterers are themselves unaware of the disorder. The problems of definition, symptomatology, aetiology and relationship to stuttering and hereditary aspects, are discussed. A preliminary case report of a family in which cluttering appears to follow a dominant mode of inheritance, is given. It is concluded that the major symptoms underlying the general cluttering syndrome in the family described, are related to some form of psychoneurological dysfunction with emphasis on a central language imbalance.S. Afr. Med. J., 48, 1624 (1974)
A clinical delineation of Tachyphemia (cluttering)
Cluttering constitutes one of the most important disorders of speech, language and communication in general. The majority of c1utterers are themselves unaware of the disorder. The problems of definition, symptomatology, aetiology and relationship to stuttering and hereditary aspects, are discussed. A preliminary case report of a family in which cluttering appears to follow a dominant mode of inheritance, is given. It is concluded that the major symptoms underlying the general cluttering syndrome in the family described, are related to some form of psychoneurological dysfunction with emphasis on a central language imbalance.S. Afr. Med. J., 48, 1624 (1974
Changes in Carbohydrates in Nursery-Grown Grapevine Rootstocks
The utilisation and accumulation of sugar, starch and hemicellulose were studied in nursery-grown grapevine rootstocks. For an initial period lasting about 12 weeks all three components were utilised to varying degrees by the cuttings. Subsequently, starch and hemicellulose increased in the stem (original cutting) of the plant, while sugar remained low until the onset of winter. In the shoots, hemicellulose accumulation was very marked, whereas in the roots starch was the dominant carbohydrate component
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