Title: Fluctuations at work: extracting more than the free energy difference from a micro-oscillator
Speaker: Dr. Nicolas Barros (Laboratoire de Physique de l'ENS de Lyon)
Host: Prof. Cheng-Hung Chang (NYCU)
Time: 14:00, October 2 (FRI.), 2026
Place: Rm. 307, 3F, Cosmology Hall, NTU

Abstract:
According to the second law of thermodynamics, driving a system between two equilibrium states costs, on average, at least their free energy difference ΔF. In small systems, however, thermal fluctuations turn work into a random variable, and the second law only holds on average: individual realizations can cost less than ΔF. We show experimentally that optimized protocols can make such events the rule rather than the exception, while 〈W〉 ≥ ΔF remains satisfied on average.
 

The measurement is performed using an underdamped micro-cantilever evolving in a virtual double-well potential created by a feedback loop, whose barrier and asymmetry can be tuned at will. With suitable parameters, more than 95% of the trajectories are performed with W < ΔF. Very fast protocols are the key to this result, which is explained by the Jarzynski equality. Finally, we show how tuning the stiffness of the oscillator opens new ways to extract work from thermal fluctuations, with first steps towards a single-particle heat engine.