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Breitenfurt bei Wien, Austria

Kohnen M.,Imperial College London | Succo M.,Imperial College London | Petrov P.G.,Imperial College London | Nyman R.A.,Imperial College London | And 3 more authors.
Nature Photonics | Year: 2011

Photonic chips that integrate optical elements on a single device can process vast amounts of information rapidly. A new branch of this technology involves coupling light to cold atoms or Bose-Einstein condensates, the quantum nature of which provides a basis for new information-processing methods. The use of optical waveguides gives the light a small cross-section, making coupling to atoms efficient. In this Letter, we present the first waveguide chip designed to address a Bose-Einstein condensate along a row of independent junctions, which are separated by only 10 μm and have large atom-photon coupling. We describe a fully integrated, scalable design, and demonstrate 11 junctions working as intended, using a low-density cold atom cloud with as little as one atom on average in any one junction. The device suggests new possibilities for engineering quantum states of matter and light on a microscopic scale. © 2011 Macmillan Publishers Limited. All rights reserved. Source

Sen D.,Bhabha Atomic Research Center | Melo J.S.,Bhabha Atomic Research Center | Bahadur J.,Bhabha Atomic Research Center | Mazumder S.,Bhabha Atomic Research Center | And 5 more authors.
Soft Matter | Year: 2011

Self-assembled grains of mixed colloids have been synthesized using evaporation induced self-assembly (EISA) by spray drying. We demonstrate using electron microscopy and small-angle neutron scattering experiments that buckling driven sphere to deformed-doughnut like morphological transformation in such a process can be arrested by proper tuning of the surface charge on the colloidal components. The buckling amplitude diminishes with a reduction in stabilization force between the colloidal particles. It is established that such arrest of morphological transformation is related to an effective exposure of the surface of softer component at gas-liquid interface. Scattering experiments confirm relatively more compact structure of the non-buckled grains compared to that of the buckled grains. A plausible mechanism regarding the arrest of morphological transformation by surface charge tuning is illustrated. © 2011 The Royal Society of Chemistry. Source

Sen D.,Bhabha Atomic Research Center | Bahadur J.,Bhabha Atomic Research Center | Das A.,Bhabha Atomic Research Center | Mazumder S.,Bhabha Atomic Research Center | And 3 more authors.
Colloids and Surfaces B: Biointerfaces | Year: 2015

We have synthesized nano-structured silica-. Escherichia coli composite micro-granules by spray drying of mixed suspension of silica and E. coli through evaporation-induced assembly. Synthesized micro-granules were subjected to calcination in order to form shape-matched macro-pores by removing the bacterial cells. The optimization of calcination temperature is crucial because calcination process leads to two contrasting effects, namely, (i) removal of E. coli from the granules and (ii) alteration of mesoscopic structure in the silica network. We have used small-angle neutron scattering and thermo-gravimetric analysis to determine the optimum temperature for calcination of these granules. It was found that calcination in the temperature range of 200. °C to 400. °C removes the cells without significant alteration of the nano-structured silica network. However, beyond 500. °C, calcination results significant coalescence between the silica particles. Calcination at 600. °C eventually collapses the meso-pore network of silica interstices. © 2015 Elsevier B.V. Source

Laliotis A.,Imperial College London | Laliotis A.,University of Paris 13 | Trupke M.,Imperial College London | Trupke M.,Atominstitut der Osterreichischen Universitaten | And 4 more authors.
Journal of Micromechanics and Microengineering | Year: 2012

Miniature concave hollows, made by wet etching silicon through a circular mask, can be used as mirror substrates for building optical micro-cavities on a chip. In this paper, we investigate how inductively coupled plasma (ICP) polishing improves both shape and roughness of the mirror substrates. We characterize the evolution of the surfaces during the ICP polishing using white-light optical profilometry and atomic force microscopy. A surface roughness of 1 nm is reached, which reduces to 0.5 nm after coating with a high reflectivity dielectric. With such smooth mirrors, the optical cavity finesse is now limited by the shape of the underlying mirror. © 2012 IOP Publishing Ltd. Source

Grond J.,University of Graz | Schmiedmayer J.,Atominstitut der Osterreichischen Universitaten | Hohenester U.,University of Graz
Physica E: Low-Dimensional Systems and Nanostructures | Year: 2010

We apply optimal control theory to the dynamic splitting process of a Bose-Einstein condensate (BEC). Number squeezing of two spatially separated BECs is important for interferometry applications and inhibits phase diffusion due to the nonlinear atom-atom interactions. We show how optimal number squeezing can be obtained on time scales much shorter compared to adiabatic splitting. The non-adiabatic time evolution of the condensates is controlled via the trap geometry, thus making our control schemes directly applicable to experiments. We find that the optimal solution for the trap is oscillatory, where a counterintuitive shaking during the ramp produces highly squeezed states. The underlying process can be identified as a parametric amplification. © 2009 Elsevier B.V. All rights reserved. Source

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