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 $D_{21}=8 f_{\rm HFS}({2S}) - f_{\rm HFS}({1S})=48 953(3)$ 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 $1S$-$2S$ transition frequency $\nu_{\rm {H}}$ in atomic hydrogen. A comparison with the result of the previous measurement performed in 1999 sets a limit of $(-29\pm 57)$ Hz for the drift of $\nu_{\rm {H}}$ with respect to the ground state hyperfine splitting $\nu_{{\rm {Cs}}}$ in $^{133}$Cs. Combining this result with the recently published optical transition frequency in $^{199}$Hg$^+$ against $\nu_{\rm {Cs}}$ and a microwave $^{87}$Rb and $^{133}$Cs clock comparison, we deduce separate limits on $\dot{\alpha}/\alpha = (-0.9\pm 2.9)\times 10^{-15}$ yr$^{-1}$ and the fractional time variation of the ratio of Rb and Cs nuclear magnetic moments $\mu_{\rm {Rb}}/\mu_{\rm {Cs}}$ equal to $(-0.5 \pm 1.7)\times 10^{-15}$ yr$^{-1}$. 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