4,239 research outputs found
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 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 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
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