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Murrell M.P.,James Franck Institute | Murrell M.P.,University Pierre and Marie Curie | Murrell M.P.,French National Center for Scientific Research | Murrell M.P.,University Paris - Sud | And 13 more authors.
Nature Physics | Year: 2014

Mechanical forces generated by cells modulate global shape changes required for essential life processes, such as polarization, division and spreading. Although the contribution of the cytoskeleton to cellular force generation is widely recognized, the role of the membrane is considered to be restricted to passively transmitting forces. Therefore, the mechanisms by which the membrane can directly contribute to cell tension are overlooked and poorly understood. To address this, we directly measure the stresses generated during liposome adhesion. We find that liposome spreading generates large traction stresses on compliant substrates. These stresses can be understood as the equilibration of internal, hydrostatic pressures generated by the enhanced membrane tension built up during adhesion. These results underscore the role of membranes in the generation of mechanical stresses on cellular length scales and that the modulation of hydrostatic pressure due to membrane tension and adhesion can be channelled to perform mechanical work on the environment. © 2014 Macmillan Publishers Limited.

Gillett G.G.,Queensland University of Technology | Dalton R.B.,Queensland University of Technology | Lanyon B.P.,Queensland University of Technology | Almeida M.P.,Queensland University of Technology | And 7 more authors.
Physical Review Letters | Year: 2010

A goal of the emerging field of quantum control is to develop methods for quantum technologies to function robustly in the presence of noise. Central issues are the fundamental limitations on the available information about quantum systems and the disturbance they suffer in the process of measurement. In the context of a simple quantum control scenario-the stabilization of nonorthogonal states of a qubit against dephasing-we experimentally explore the use of weak measurements in feedback control. We find that, despite the intrinsic difficultly of implementing them, weak measurements allow us to control the qubit better in practice than is even theoretically possible without them. Our work shows that these more general quantum measurements can play an important role for feedback control of quantum systems. © 2010 The American Physical Society.

Jennewein T.,University of Waterloo | Jennewein T.,Queensland University of Technology | Jennewein T.,Austrian Academy of Sciences | Barbieri M.,Queensland University of Technology | And 2 more authors.
Journal of Modern Optics | Year: 2011

Photonics is a promising architecture for the realisation of quantum information processing, since the two-photon interaction, or non-linearity, necessary to build logical gates can efficiently be realised by the use of interference with ancillary photons and detection 1. Although single-photon sources and detectors are pivotal in realisations of such systems, clear guidelines for the required performance of realistic systems are yet to be defined. We present our detailed numerical simulation of several quantum optics circuits including sources and detectors all represented in multi-dimensional Fock-spaces, which allows us to obtain experimentally realistic performance bounds for these devices. In addition, the single-photon source based on switched parametric down-conversion is studied, which in principle could reach the required performance. Three approaches for implementing the switching hierarchy of the photons are simulated, and their anticipated performance is obtained. Our results define the bar for the optical devices needed to achieve the first level of linear-optics quantum computing outside the coincidence basis. © 2011 Taylor & Francis.

Hebert M.,Jean Monnet University | Hebert M.,Institute dOptique
Proceedings of SPIE - The International Society for Optical Engineering | Year: 2014

The well-known Yule-Nielsen modified spectral Neugebauer model is one of the most accurate predictive models for the spectral reflectance of printed halftone colors which expresses the spectral reflectance of halftones raised to the power 1/n as a linear combination of the spectral reflectance of the fulltone colors (Neugebauer primaries) also raised to the power 1/n, where n is a tunable real number. The power 1/n transform, characteristic of the Yule-Nielsen transform, empirically models the nonlinear relationship between the spectral reflectances of halftones and fulltones due to the internal propagation of light by scattering into the printing support, a phenomenon known as "optical dot gain" or "Yule-Nielsen effect". In this paper, we propose a graphical method permitting to observe this non-linear relationship in the case of single-ink halftones and to experimentally check the capacity of the Yule-Nielsen model to predict it accurately. In the case where the Yule-Nielsen transform is not well adapted to the considered type of prints, we propose alternative transforms in order to improve the prediction accuracy. © 2014 SPIE-IS&T.

Institute Doptique and Thales Alenia | Date: 2010-05-03

Techniques for identifying images of a scene including illuminating the scene with a beam of 3 or more wavelengths, polarized according to a determined direction; simultaneously acquiring for each wavelength an image X_(//)(_(i)) polarized according to said direction and an image X_()(_(i)) polarized according to a direction perpendicular to said direction, X_()(_(i)) being spatially distinct from X_(//)(_(i)); calculating for each wavelength an intensity image which is a linear combination of X_(//)(_(i)) and X_()(_(i)), providing an intensity spectrum for each pixel; calculating for each wavelength a polarization contrast image on the basis of an intensity ratio calculated as a function of X_(//)(_(i)) and of X_()(_(i)), providing a polarization contrast spectrum for each pixel; and calculating a spectro-polarimetric contrast image of the scene, each pixel of this spectro-polarimetric contrast image calculated based on the intensity spectrum and the contrast spectrum of the pixel considered.

Fabbri N.,University of Florence | Panfil M.,International School for Advanced Studies | Panfil M.,University of Amsterdam | Clement D.,Institute dOptique | And 7 more authors.
Physical Review A - Atomic, Molecular, and Optical Physics | Year: 2015

Interactions are known to have dramatic effects on bosonic gases in one dimension (1D). Not only does the ground state transform from a condensate like state to an effective Fermi sea, but new fundamental excitations, which do not have any higher-dimensional equivalents, are predicted to appear. In this work, we trace these elusive excitations via their effects on the dynamical structure factor of 1D strongly interacting Bose gases at low temperature. An array of 1D Bose gases is obtained by loading a 87Rb condensate in a two-dimensional lattice potential. The dynamical structure factor of the system is probed by energy deposition through low-momentum Bragg excitations. The experimental signals are compared to recent theoretical predictions for the dynamical structure factor of the Lieb-Liniger model at T>0. Our results demonstrate that the main contribution to the spectral widths stems from the dynamics of the interaction-induced excitations in the gas, which cannot be described by the Luttinger liquid theory. © 2015 American Physical Society.

Huber F.,University of Leipzig | Huber F.,FOM Institute for Atomic and Molecular Physics | Strehle D.,University of Leipzig | Strehle D.,Institute dOptique | And 2 more authors.
New Journal of Physics | Year: 2015

Biopolymer networks contribute mechanical integrity as well as functional organization to living cells. One of their major constituents, the protein actin, is present in a large variety of different network architectures, ranging from extensive networks to densely packed bundles. The shape of the network is directly linked to its mechanical properties and essential physiological functions. However, a profound understanding of architecture-determining mechanisms and their physical constraints remains elusive. We use experimental bottom-up systems to study the formation of confined actin networks by entropic forces. Experiments based on molecular crowding as well as counterion condensation reveal a generic tendency of homogeneous filament solutions to aggregate into regular actin bundle networks connected by aster-like centers. The network architecture is found to critically rely on network formation history. Starting from identical biochemical compositions, we observe drastic changes in network architecture as a consequence of initially biased filament orientation or mixing-induced perturbations. Our experiments suggest that the tendency to form regularly spaced bundle networks is a rather general feature of isotropic, homogeneous filament solutions subject to uniform attractive interactions. Due to the fundamental nature of the considered interactions, we expect that the investigated type of network formation further implies severe physical constraints for cytoskeleton self-organization on the more complex level of living cells. © 2015 IOP Publishing Ltd and Deutsche Physikalische Gesellschaft.

Chevalier P.,CNRS Laboratory for Photonics and Nanostructures | Chevalier P.,ONERA | Bouchon P.,ONERA | Greffet J.-J.,Institute dOptique | And 4 more authors.
Physical Review B - Condensed Matter and Materials Physics | Year: 2014

Inspired by the acoustic Helmholtz resonator, we propose a slit-box electromagnetic nanoantenna able to concentrate the energy of an incident beam into surfaces a thousand times smaller than with a classical lens. This design produces a giant electric field enhancement throughout the slit. The intensity enhancement reaches 104 in the visible range up to 108 in the THz range even with focused beams, thanks to an omnidirectional reception. These properties could target applications requiring extreme light concentration, such as surface-enhanced infrared absorption, nonlinear optics, and biophotonics. © 2014 American Physical Society.

Jonas A.,Koç University | Karadag Y.,Koç University | Mestre M.,Koç University | Mestre M.,Institute dOptique | Kiraz A.,Koç University
Journal of the Optical Society of America B: Optical Physics | Year: 2012

We report measurements of ultrahigh quality factors (Q-factors) of the optical whispering-gallery modes excited via a tapered optical-fiber waveguide in single glycerol-water microdroplets standing on a superhydrophobic surface in air. Owing to the high contact angle of the glycerol-water mixture on the superhydrophobic surface (≥155°), microdroplets with the geometry of a truncated sphere minimally distorted by gravity and contact line pinning effects could be generated. Q-factors up to 2.3 × 106 were observed for such droplets with radii of 100-200 μm exposed to the ambient atmosphere in a closed chamber with controlled relative humidity. Placement of microdroplets in a constant humidity environment permitted prolonged characterization of Q-factors for individual microdroplets. We found that the Q-factors in air were stable over more than 1 h and their measured values were limited mostly by the thermally induced droplet shape fluctuations. © 2012 Optical Society of America.

Aspect A.,Institute dOptique
Proceedings of the 25th Solvay Conference on Physics: The Theory of the Quantum World | Year: 2013

I ask the question: What can we infer about the nature and structure of the physical world (a) from experiments already done to test the predictions of quantum mechanics (b) from the assumption that all future experiments will agree with those predictions? I discuss existing and projected experiments related to the two classic paradoxes of quantum mechanics, named respectively for EPR and Schrödinger's Cat, and show in particular that one natural conclusion from both types of experiment implies the abandonment of the concept of macroscopic counterfactual definiteness.

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