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Fluctuations and Interactions of Brownian particles in multiple Optical Traps

Abstract : We experimentally study the fluctuations of Brownian micro-particles trapped with optical tweezers arranged in various spatial configurations. We give a general description of the set-up and detail four different experiments we conducted. We first use a single particle in a double-well potential to model a two-state memory system. We verify the Landauer principle on the minimal energetic cost to erase one bit of information, and we use a detailed version of a fluctuation theorem to retrieve the expected energetic bound. We then use two particles in two different traps to study the hydrodynamic interactions between two systems kept at different effective temperatures. Contrary to what was previously observed, we show that the sol-gel transition of gelatine does not provide any anomalous fluctuations for the trapped particle when the sample is quenched below gelification temperature. However, we show that an effective temperature is created when a well chosen random noise is added on one trap position. We demonstrate that the random forcing on one particle induces an instantaneous correlation between the two particles motions, and an energy exchange from the virtually hot particle to the cold one, which is in equilibrium with the thermal bath. We show a good agreement between the experimental data and the predictions from an hydrodynamic coupling model. Finally, we describe the use of micro-fluidic channels to create a shear flow at the micron size, and we discuss the possibility to interpret the force due to the shear-flow in terms of an effective temperature by testing a fluctuation-dissipation relation.
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Submitted on : Thursday, September 3, 2015 - 2:37:05 PM
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  • HAL Id : tel-01192759, version 1

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Antoine Bérut. Fluctuations and Interactions of Brownian particles in multiple Optical Traps. Condensed Matter [cond-mat]. Ecole normale supérieure de lyon - ENS LYON, 2015. English. ⟨NNT : 2015ENSL1003⟩. ⟨tel-01192759⟩

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