Experimental investigations of stochastic thermodynamics

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Nearly 150 years ago, Maxwell first asked what happens when a “neat fingered being” - a demon - uses information to extract work from heat. The Second Law of Thermodynamics should forbid this, but how? The question has galled physicists and provoked debate for over a century. One year ago in my laboratory, we made a definitive measurement that confirms a hypothesis proposed 50 years ago: that Maxwell demons need to erase information and that erasing information requires dissipating as much energy as is gained. The work proposed here pursues these ideas to cases where systems are out of equilibrium. One important goal is to be able to measure the form of the function that describes the entropy of a system out of equilibrium. It has been proposed, but never directly tested, that the Shannon entropy plays this role. The function superficially looks like the standard 19th century Gibbs-Boltzmann expression for the entropy but applies out of equilibrium. The work I propose takes advantage of the feedback trap, a device that my group and I developed into a high-precision instrument during my current Discovery Grant. We will continue to improve this trap and will also take advantage of its abilities to mimic an arbitrary time-dependent potential (or even a force field that does not come from a potential) to carry out a range of experiments that lie at the intersection of nonequilibrium statistical physics, control, and information theory. Projects include optimal control - how to carry out a task (such as erasing information) in a finite time while doing the least possible amount of work; Onsager coefficients and their symmetries (and lack thereof) for periodically modulated potentials; and inferences that can suddenly change as more information is acquired - the Eureka moment. We will test the idea that learning need not be a slow, steady process but can proceed by distinct jumps. We will also explore diffusion in more complex settings, such as near a wall. Subtle things happen - motion becomes different in different directions, for example. We will look at this in three settings: a magnetic bead, a rod-shaped particle, and DNA (which balls up like a sphere but can deform near a wall). In all of these experiments, the overall goal is to establish, for the 21st century, the kind of science that thermodynamics was to 18th century steam engines. Such a science would explain what is possible in small systems, what is not, and how to achieve the greatest possible efficiencies. It will marry the advances in technology at micro- and nanoscales with an understanding of how machines, motors, and other devices work in a setting where thermal fluctuations are huge but where reliable decisions still must be made. These are questions that underlie our understanding of biology and life as well as engineering at small scales. They provide valuable opportunities to train HQP at all levels for Canada’s technologies and jobs of the future.