Thermodynamics of nonequilibrium systems with uncertain parameters

TL;DR

This paper extends stochastic thermodynamics to systems with uncertain parameters, defining effective thermodynamic quantities through averaging over all transition rates satisfying detailed balance, and explores the implications for the second law and work bounds.

Contribution

It formalizes the treatment of parameter uncertainty in stochastic thermodynamics, deriving new bounds and fluctuation theorems for such systems.

Findings

Effective entropy can violate the second law under uncertainty.

Expected stochastic entropy obeys the second law despite parameter uncertainty.

Derived bounds on maximal work extractable with uncertain temperatures.

Abstract

In the real world, one almost never knows the parameters of a thermodynamic process to infinite precision. Reflecting this, here we investigate how to extend stochastic thermodynamics to systems with uncertain parameters, including uncertain number of heat baths / particle reservoirs, uncertainty in the precise values of temperatures / chemical potentials of those reservoirs, uncertainty in the energy spectrum, uncertainty in the control protocol, etc. We formalize such uncertainty with an (arbitrary) probability measure over all transition rate matrices satisfying local detailed balance. This lets us define the effective thermodynamic quantities by averaging over all LDB-obeying rate matrices. We show that the resultant effective entropy violates the second law of thermodynamics. In contrast to the effective entropy though, the expected stochastic entropy, defined as the ensemble average of the effective trajectory-level entropy, satisfies the second law. We then and explicitly calculate the second-order correction to the second law for the case of one heat bath with uncertain temperature. We also derive the detailed fluctuation theorem for expected effective trajectory entropy production for this case, and derive a lower bound for the associated expected work. Next, to ground these formal considerations with experimentally testable bounds on allowed energetics, we derive a bound on the maximal work that can be extracted from systems with arbitrarily uncertain temperature. We end by extending previous work on "thermodynamic value of information", to allow for uncertainty in the time-evolution of the rate matrix.