Thermodynamics of computations with absolute irreversibility, unidirectional transitions, and stochastic computation times

TL;DR

This paper develops a thermodynamic framework for computation that accounts for unidirectional transitions, stochastic halting times, and initial conditions, providing universal bounds on dissipation applicable to digital computers and automata.

Contribution

It extends non-equilibrium thermodynamics to non-stationary Markov processes with irreversibility, deriving universal fluctuation relations and bounds relevant for real-world computational systems.

Findings

Derived universal fluctuation relations and inequalities for dissipation.

Provided bounds on acceptance probabilities of automata based on thermodynamics.

Connected computational processes with stochastic thermodynamics and resetting mechanisms.

Abstract

Developing a thermodynamic theory of computation is a challenging task at the interface of non-equilibrium thermodynamics and computer science. In particular, this task requires dealing with difficulties such as stochastic halting times, unidirectional (possibly deterministic) transitions, and restricted initial conditions, features common in real-world computers. Here, we present a framework which tackles all such difficulties by extending the martingale theory of non-equilibrium thermodynamics to generic non-stationary Markovian processes, including those with broken detailed balance and/or absolute irreversibility. We derive several universal fluctuation relations and second-law-like inequalities that provide both lower and upper bounds on the intrinsic dissipation (mismatch cost) associated with any periodic process -- in particular the periodic processes underlying all current digital computation. Crucially, these bounds apply even if the process has stochastic stopping times, as it does in many computational machines. We illustrate our results with exhaustive numerical simulations of deterministic finite automata (DFA) processing bit strings, one of the fundamental models of computation from theoretical computer science. We also provide universal equalities and inequalities for the acceptance probability of words of a given length by a deterministic finite automaton in terms of thermodynamic quantities, and outline connections between computer science and stochastic resetting. Our results, while motivated from the computational context, are applicable far more broadly.