10,624 research outputs found
Atom detection and photon production in a scalable, open, optical microcavity
A microfabricated Fabry-Perot optical resonator has been used for atom
detection and photon production with less than 1 atom on average in the cavity
mode. Our cavity design combines the intrinsic scalability of microfabrication
processes with direct coupling of the cavity field to single-mode optical
waveguides or fibers. The presence of the atom is seen through changes in both
the intensity and the noise characteristics of probe light reflected from the
cavity input mirror. An excitation laser passing transversely through the
cavity triggers photon emission into the cavity mode and hence into the
single-mode fiber. These are first steps towards building an optical
microcavity network on an atom chip for applications in quantum information
processing.Comment: 4 pages, 4 figures. A typographical error in the published paper has
been corrected (equation of the corrected normalized variance, page 3, 2nd
paragraph
Dynamics of diluted magnetic semiconductors from atomistic spin dynamics simulations: Mn doped GaAs as a case study
The dynamical behavior of the magnetism of diluted magnetic semiconductors
(DMS) has been investigated by means of atomistic spin dynamics simulations.
The conclusions drawn from the study are argued to be general for DMS systems
in the low concentration limit, although all simulations are done for 5%
Mn-doped GaAs with various concentrations of As antisite defects. The
magnetization curve, , and the Curie temperature have been
calculated, and are found to be in good correspondence to results from Monte
Carlo simulations and experiments. Furthermore, equilibrium and non-equilibrium
behavior of the magnetic pair correlation function have been extracted. The
dynamics of DMS systems reveals a substantial short ranged magnetic order even
at temperatures at or above the ordering temperature, with a non-vanishing pair
correlation function extending up to several atomic shells. For the high As
antisite concentrations the simulations show a short ranged anti-ferromagnetic
coupling, and a weakened long ranged ferromagnetic coupling. For sufficiently
large concentrations we do not observe any long ranged ferromagnetic
correlation. A typical dynamical response shows that starting from a random
orientation of moments, the spin-correlation develops very fast ( 1ps)
extending up to 15 atomic shells. Above 10 ps in the simulations, the
pair correlation is observed to extend over some 40 atomic shells. The
autocorrelation function has been calculated and compared with ferromagnets
like bcc Fe and spin-glass materials. We find no evidence in our simulations
for a spin-glass behaviour, for any concentration of As antisites. Instead the
magnetic response is better described as slow dynamics, at least when compared
to that of a regular ferromagnet like bcc Fe.Comment: 24 pages, 15 figure
The effect of multiple paternity on genetic diversity during and after colonisation
In metapopulations, genetic variation of local populations is influenced by
the genetic content of the founders, and of migrants following establishment.
We analyse the effect of multiple paternity on genetic diversity using a model
in which the highly promiscuous marine snail Littorina saxatilis expands from a
mainland to colonise initially empty islands of an archipelago. Migrant females
carry a large number of eggs fertilised by 1 - 10 mates. We quantify the
genetic diversity of the population in terms of its heterozygosity: initially
during the transient colonisation process, and at long times when the
population has reached an equilibrium state with migration. During
colonisation, multiple paternity increases the heterozygosity by 10 - 300 % in
comparison with the case of single paternity. The equilibrium state, by
contrast, is less strongly affected: multiple paternity gives rise to 10 - 50 %
higher heterozygosity compared with single paternity. Further we find that far
from the mainland, new mutations spreading from the mainland cause bursts of
high genetic diversity separated by long periods of low diversity. This effect
is boosted by multiple paternity. We conclude that multiple paternity
facilitates colonisation and maintenance of small populations, whether or not
this is the main cause for the evolution of extreme promiscuity in Littorina
saxatilis.Comment: 7 pages, 5 figures, electronic supplementary materia
Identifying single electron charge sensor events using wavelet edge detection
The operation of solid-state qubits often relies on single-shot readout using
a nanoelectronic charge sensor, and the detection of events in a noisy sensor
signal is crucial for high fidelity readout of such qubits. The most common
detection scheme, comparing the signal to a threshold value, is accurate at low
noise levels but is not robust to low-frequency noise and signal drift. We
describe an alternative method for identifying charge sensor events using
wavelet edge detection. The technique is convenient to use and we show that,
with realistic signals and a single tunable parameter, wavelet detection can
outperform thresholding and is significantly more tolerant to 1/f and
low-frequency noise.Comment: 11 pages, 4 figure
Oscillator Strengths and Damping Constants for Atomic Lines in the J and H Bands
We have built a line list in the near-infrared J and H bands (1.00-1.34,
1.49-1.80 um) by gathering a series of laboratory and computed line lists.
Oscillator strengths and damping constants were computed or obtained by fitting
the solar spectrum.
The line list presented in this paper is, to our knowledge, the most complete
one now available, and supersedes previous lists.Comment: Accepted, Astrophysical Journal Supplement, tentatively scheduled for
the Sep. 1999 Vol. 124 #1 issue. Text and tables also available at
http://www.iagusp.usp.br/~jorge
Deltagardriven forskning â VĂ€xtodlingsgruppen, resultat och utvĂ€rdering av arbetet under 1998 till 2001
DÄ arbetet i vÀxtodlingsgruppen pÄbörjades var förvÀntningarna pÄ deltagardriven forskning att den sammanlagda erfarenheten hos lantbrukare, forskare och rÄdgivare skulle bidra till utförandet av relevanta gÄrdsförsök. Lantbrukarna önskade dessutom strÀva efter att öka och vidarebefordra den kunskap som fanns i gruppen, samt att fÄ etablerade forskare att undersöka omrÄden som praktikerna upplever som viktiga och svÄra.
Redan i initialskedet slog vÀxtodlingsgruppen fast att arbeta för att gemensamt identifiera problem och anvÀnda relevanta forskningsmetoder pÄ gÄrdsnivÄ. Syftet var att genom olika odlingsÄtgÀrder kunna förbÀttra förutsÀttningarna för ekologisk vÀxtodling. Ett mÄl var att finna effektiva metoder för optimal vÀxtnÀringstillförsel i ekologisk produktion pÄ lerjordar i MÀlardalen. För nÀrvarande saknas bra underlag för hur kvÀveleveransen varierar under sÀsongen framförallt till strÄsÀd. Detta pÄverkar i sin tur bÄde skördeutfall, proteinhalt, miljöbelastning och ekonomi. Ett annat mÄl var att kunna reglera ogrÀsförekomsten, frÀmst kvickrot och tistel, pÄ ett effektivt sÀtt i vÀxtföljden.
Motivationen för lantbrukarna har under projektets gÄng varit att frÀmja det ekologiska lantbruket som helhet. Detta har möjliggjorts genom erfarenhetsutbyte pÄ grupptrÀffar kombinerat med gÄrdsbesök dÀr lantbrukarnas intressen och frÄgestÀllningar har varit drivande. VÀxtodlingsgruppen har pÄ sÄ vis initialt bidragit till ett lokalt utvecklingsarbete och en uppbyggnad av ökat kunnande inom ekologiskt vÀxtodling
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