Identification of asymmetric current fluctuations in small systems

Theories of stochastic dynamics often used to model the behavior of mesoscopic and nanoscale systems predict temporal asymmetry in fluctuations of their properties when such systems are out of equilibrium. For example, in a system where a fluctuating current is produced, the way the current rises is different to the way in which it falls. Since mesoscopic systems can be considered as a collection of microscopic systems, we are led to ask: is this a fictitious effect of stochastic models, or does this asymmetry in the fluctuations even occur in more fundamental molecular level models, which are deterministic and reversible? Here we provide clear numerical evidence that asymmetric fluctuations do occur in nonequilibrium steady state molecular dynamics. In previous work, we observed fluctuations with asymmetric behavior in a microscopic system of particles undergoing Couette flow. We now extend our observations to a microscopic system of particles subject to color field, to verify that the presence of asymmetry in fluctuations holds more generally for reversible microscopic samples of matter out of equilibrium