Extreme sub-wavelength atom localization via coherent population trapping

We demonstrate an atom localization scheme based on monitoring of the atomic coherences. We consider atomic transitions in a Lambda configuration where the control field is a standing wave field. The probe field and the control field produce coherence between the two ground states. We show that this coherence has the same fringe pattern as produced by a Fabry-Perot interferometer and thus measurement of the atomic coherence would localize the atom. Interestingly enough the role of the cavity finesse is played by the ratio of the intensities of the pump and probe. This is in fact the reason for obtaining extreme subwavelenth localization. We suggest several methods to monitor the produced localization.Comment: 6 pages, 5 figure

Raoult's Formalism in Understanding Low Temperature Growth of GaN Nanowires using Binary Precursor

Growth of GaN nanowires are carried out via metal initiated vapor-liquid-solid mechanism, with Au as the catalyst. In chemical vapour deposition technique, GaN nanowires are usually grown at high temperatures in the range of 900-1100 ^oC because of low vapor pressure of Ga below 900 ^oC. In the present study, we have grown the GaN nanowires at a temperature, as low as 700 ^oC. Role of indium in the reduction of growth temperature is discussed in the ambit of Raoult's law. Indium is used to increase the vapor pressure of the Ga sufficiently to evaporate even at low temperature initiating the growth of GaN nanowires. In addition to the studies related to structural and vibrational properties, optical properties of the grown nanowires are also reported for detailed structural analysis.Comment: 24 pages, 7 figures, journa

A detailed analysis of structure growth in f(R)f(R) theories of gravity

We investigate the connection between dark energy and fourth order gravity by analyzing the behavior of scalar perturbations around a Friedmann-Robertson-Walker background. The evolution equations for scalar perturbation are derived using the covariant and gauge invariant approach and applied to two widely studied $f(R)$ gravity models. The structure of the general fourth order perturbation equations and the analysis of scalar perturbations lead to the discovery of a characteristic signature of fourth order gravity in the matter power spectrum, the details of which have not seen before in other works in this area. This could provide a crucial test for fourth order gravity on cosmological scales.Comment: 27 pages and 35 figure