217 research outputs found
Room temperature emission at 1.6 µm from InGaAs quantum dots capped with GaAsSb
Room temperature photoluminescence at 1.6 µm is demonstrated from InGaAs quantum dots capped with an 8 nm GaAsSb quantum well. Results obtained from various sample structures are compared, including samples capped with GaAs. The observed redshift in GaAsSb capped samples is attributed to a type II band alignment and to a beneficial modification of growth kinetics during capping due to the presence of Sb. The sample structure is discussed on the basis of transmission electron microscopy results.This work was supported by the Spanish MCyT under NANOSELF project TIC2002-04096, by CAM project GR/MAT/0726/2004, by the SANDiE Network of excellence (Contract No. NMP4-CT-2004-500101) and the Junta de Andalucía
(Group Tep-0120). J.M.R. acknowledges support
through a Ramón y Cajal grant. TEM measurements were carried out at DME-SCCYT, UCA.Peer reviewe
New Measurement of the 2S Hyperfine Interval in Atomic Hydrogen
An optical measurement of the 2S hyperfine interval in atomic hydrogen using
two-photon spectroscopy of the 1S-2S transition gives a value of 177 556
834.3(6.7) Hz. The uncertainty is
2.4 times smaller than achieved by our group in 2003 and more than 4 times
smaller than for any independent radio-frequency measurement. The specific
combination of the 2S and 1S hyperfine intervals predicted by QED theory
Hz is in good
agreement with the value of 48 923(54) Hz obtained from this experiment.Comment: 4 pages, 4 figure
New Limits to the Drift of Fundamental Constants from Laboratory Measurements
We have remeasured the absolute - transition frequency in atomic hydrogen. A comparison with the result of the previous
measurement performed in 1999 sets a limit of Hz for the drift of
with respect to the ground state hyperfine splitting in Cs. Combining this result with the recently published
optical transition frequency in Hg against and a
microwave Rb and Cs clock comparison, we deduce separate limits
on yr and the
fractional time variation of the ratio of Rb and Cs nuclear magnetic moments
equal to
yr. The latter provides information on the temporal behavior of the
constant of strong interaction.Comment: 4 pages, 3 figures, LaTe
Optical Clocks in Space
The performance of optical clocks has strongly progressed in recent years,
and accuracies and instabilities of 1 part in 10^18 are expected in the near
future. The operation of optical clocks in space provides new scientific and
technological opportunities. In particular, an earth-orbiting satellite
containing an ensemble of optical clocks would allow a precision measurement of
the gravitational redshift, navigation with improved precision, mapping of the
earth's gravitational potential by relativistic geodesy, and comparisons
between ground clocks.Comment: Proc. III International Conference on Particle and Fundamental
Physics in Space (SpacePart06), Beijing 19 - 21 April 2006, to appear in
Nucl. Phys.
Pathway to the PiezoElectronic Transduction Logic Device
The information age challenges computer technology to process an
exponentially increasing computational load on a limited energy budget - a
requirement that demands an exponential reduction in energy per operation. In
digital logic circuits, the switching energy of present FET devices is
intimately connected with the switching voltage, and can no longer be lowered
sufficiently, limiting the ability of current technology to address the
challenge. Quantum computing offers a leap forward in capability, but a clear
advantage requires algorithms presently developed for only a small set of
applications. Therefore, a new, general purpose, classical technology based on
a different paradigm is needed to meet the ever increasing demand for data
processing.Comment: in Nano Letters (2015
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