Sergio Ciliberto

Experimental verification of Landauer/'s principle linking information and thermodynamics

In 1961, Rolf Landauer argued that the erasure of information is a dissipative process. A minimal quantity of heat, proportional to the thermal energy and called the Landauer bound, is necessarily produced when a classical bit of information is deleted. A direct consequence of this logically irreversible transformation is that the entropy of the environment increases by a finite amount. Despite its fundamental importance for information theory and computer science, the erasure principle has not been verified experimentally so far, the main obstacle being the difficulty of doing single-particle experiments in the low-dissipation regime. Here we experimentally show the existence of the Landauer bound in a generic model of a one-bit memory. Using a system of a single colloidal particle trapped in a modulated double-well potential, we establish that the mean dissipated heat saturates at the Landauer bound in the limit of long erasure cycles. This result demonstrates the intimate link between information theory and thermodynamics. It further highlights the ultimate physical limit of irreversible computation.

On the scaling of three-dimensional homogeneous and isotropic turbulence

Abstract In this paper we investigate the scaling properties of three-dimensional isotropic and homogeneous turbulence. We analyze a new form of scaling (extended self-similarity) recently introduced in the literature. We found that anomalous scaling of the velocity structure functions is clearly detectable even at a moderate and low Reynolds number and it extends over a much wider range of scales with respect to the inertial range.

Extended Self-Similarity in the Dissipation Range of Fully Developed Turbulence

In this letter we report further experimental evidence of extended self-similarity in the structure functions of the velocity field of fully developed turbulence. We study the behaviour of high-order structure functions close to the Kolmogorov scale η where extended self-similarity is observed.

Memory in the aging of a polymer glass

Low-frequency dielectric measurements on plexiglass (PMMA) show that cooling and heating the sample at constant rate give a hysteretic dependence on temperature of the dielectric constant . A temporary stop of cooling produces a downward relaxation of . Two main features are observed: i) when cooling is resumed goes back to the values obtained without the cooling stop (i.e. the low-temperature state is independent of the cooling history); ii) upon reheating keeps the memory of the aging history (Memory). The analogies and differences with similar experiments done in spin-glasses are discussed.

On the Scaling of the Velocity and Temperature Structure Functions in Rayleigh-Bénard Convection

In this letter we study, both experimentally and numerically, the scaling properties of Rayleigh-Benard turbulent convection. To this aim we develop a new methodology which is based upon the anomalous scaling, due to intermittency, of temperature and velocity structure functions.

Scaling laws for the turbulent mixing of a passive scalar in the wake of a cylinder

Turbulence is triggered by an air flow passing around a cylinder and heated by an array of hot wires parallel to the cylinder axis. Simultaneous velocity and passive temperature fluctuations are measured locally on the centerline of the cylinder wake. The focus is on the scaling properties of the mixed scalar-velocity structure functions 〈|δu(r)δθ(r)2|p/3〉. It is observed that 〈|δu(r)δθ(r)2|p/3〉 displays the same scaling behavior as 〈|δu(r)δθ(r)2|〉Ψp/Ψ3 over an extended range of scales. This yields accurate measurements for the relative scaling exponents Ψp/Ψ3. It is further observed that the moments of the coarse-grained scalar energy diffusion rate 〈N(r)p〉 satisfy a closure condition as proposed by She and Leveque [Phys. Rev. Lett. 72, 336 (1994)]. Otherwise it is proposed that 〈|δu(r)δθ(r)2|p/3〉 scales as 〈N(r)p/3〉〈|δu(r)δθ(r)2|〉p/3. This generalized similarity relation is well supported by our measurements over a range of scales which greatly exceeds the inertial range. A theoretical prediction is fin...

Interaction of sound with fast crack propagation: an equation of motion for the crack tip

Abstract The influence of ultrasound on crack dynamics in brittle materials is experimentally studied by using both the natural sound emitted by the propagating crack and an artificially generated ultrasound burst. We show that, although the acoustic energy is much weaker than the energy needed to propagate the crack, the presence of sound waves in the specimen cannot be neglected because sound interacts with the crack tip and may strongly modify the fracture dynamics. The characterization of this interaction allows us to find an equation of motion describing the crack propagation and the energy balance in mode I.

Statistical properties of the energy exchanged between two heat baths coupled by thermal fluctuations

We study both experimentally and theoretically the statistical properties of the energy exchanged between two electrical conductors, kept at different temperatures by two different heat reservoirs, and coupled by the electrical thermal noise. Such a system is ruled by the same equations as two Brownian particles kept at different temperatures and coupled by an elastic force. We measure the heat flowing between the two reservoirs and the thermodynamic work done by one part of the system on the other. We show that these quantities exhibit a long-time fluctuation theorem. Furthermore, we evaluate the fluctuating entropy, which satisfies a conservation law. These experimental results are fully justified by the theoretical analysis. Our results give more insight into the energy transfer in the famous Feynman ratchet, widely studied theoretically but never in an experiment.

Multiscale velocity correlation in turbulence: Experiments, numerical simulations, synthetic signals

Multiscale correlation functions in high Reynolds number experimental turbulence, numerical simulations, and synthetic signals are investigated. Fusion Rules predictions as they arise from multiplicative, almost uncorrelated, random processes for the energy cascade are tested. Leading and subleading contribution, in the inertial range, can be explained as arising from a multiplicative random process for the energy transfer mechanisms. Two different predictions for correlations involving dissipative observable are also briefly discussed.

Fast equilibrium switch of a micro mechanical oscillator

We demonstrate an accurate method to control the motion of a micromechanical oscillator in contact with a thermal bath. The experiment is carried out on the cantilever tip of an atomic force microscope. Applying an appropriate time dependent external force, we decrease the time necessary to reach equilibrium by two orders of magnitude compared to the intrinsic equilibration time. Finally, we analyze the energetic cost of such a fast equilibration, by measuring with kB T accuracy the energy exchanges along the process.