Publications

New Journal of Physics

Hoang, Thai H.

Feynman's ratchet is a microscopic machine in contact with two heat reservoirs, at temperatures T_A and T_B, that was proposed by Richard Feynman to illustrate the second law of thermodynamics. In equilibrium (T_A = T_B), thermal fluctuations prevent the ratchet from generating directed motion. When the ratchet is maintained away from equilibrium by a temperature difference (T_A≠T_B), it can operate as a heat engine, rectifying thermal fluctuations to perform work. While it has attracted much interest, the operation of Feynman's ratchet as a heat engine has not been realized experimentally, due to technical challenges. In this work, we realize Feynman's ratchet with a colloidal particle in a one dimensional optical trap in contact with two heat reservoirs: one is the surrounding water, while the effect of the other reservoir is generated by a novel feedback mechanism, using the Metropolis algorithm to impose detailed balance. We verify that the system does not produce work when T_A = T_B, and that it becomes a microscopic heat engine when T_A≠T_B. We analyze work, heat and entropy production as functions of the temperature difference and external load. As a result, our experimental realization of Feynman's ratchet and the Metropolis algorithm can also be used to study the thermodynamics of feedback control and information processing, the working mechanism of molecular motors, and controllable particle transportation.

Schwindt, Peter S.; Hoang, Thai H.; Jau, Yuan-Yu J.; Overstreet, Richard O.

Abstract not provided.

Schwindt, Peter S.; Hoang, Thai H.; Jau, Yuan-Yu J.; Overstreet, Richard O.

Abstract not provided.

Physical Review Letters

Hoang, Thai H.; Pan, Rui; Ahn, Jonghoon; Bang, Jaehoon; Quan, H.T.; Li, Tongcang

Nonequilibrium processes of small systems such as molecular machines are ubiquitous in biology, chemistry, and physics but are often challenging to comprehend. In the past two decades, several exact thermodynamic relations of nonequilibrium processes, collectively known as fluctuation theorems, have been discovered and provided critical insights. These fluctuation theorems are generalizations of the second law and can be unified by a differential fluctuation theorem. Here we perform the first experimental test of the differential fluctuation theorem using an optically levitated nanosphere in both underdamped and overdamped regimes and in both spatial and velocity spaces. We also test several theorems that can be obtained from it directly, including a generalized Jarzynski equality that is valid for arbitrary initial states, and the Hummer-Szabo relation. Our study experimentally verifies these fundamental theorems and initiates the experimental study of stochastic energetics with the instantaneous velocity measurement.