Optimal time estimation and the clock uncertainty relation for stochastic processes

TL;DR

This paper derives fundamental limits on the precision of time estimation in Markovian stochastic processes, revealing that the mean residual time bounds the achievable accuracy and providing tighter bounds than previous relations.

Contribution

It formulates the optimal time estimation problem for Markovian processes and derives a universal, tighter bound on precision based on mean residual time, with explicit saturating observables.

Findings

Established a universal precision bound controlled by mean residual time.

Constructed observables that saturate the precision bound.

Demonstrated the bound's tightness and its implications for non-equilibrium systems.

Abstract

Time estimation is a fundamental task that underpins precision measurement, global navigation systems, financial markets, and the organisation of everyday life. Many biological processes also depend on time estimation by nanoscale clocks, whose performance can be significantly impacted by random fluctuations. In this work, we formulate the problem of optimal time estimation for Markovian stochastic processes, and present its general solution in the asymptotic (long-time) limit. Specifically, we obtain a tight upper bound on the precision of any time estimate constructed from sustained observations of a classical, Markovian jump process. This bound is controlled by the mean residual time, i.e. the expected wait before the first jump is observed. As a consequence, we obtain a universal bound on the signal-to-noise ratio of arbitrary currents and counting observables in the steady state. This bound is similar in spirit to the kinetic uncertainty relation but provably tighter, and we explicitly construct the counting observables that saturate it. Our results establish ultimate precision limits for an important class of observables in non-equilibrium systems, and demonstrate that the mean residual time, not the dynamical activity, is the measure of freneticity that tightly constrains fluctuations far from equilibrium.