Quantum thermodynamics with uncertain equilibrium

TL;DR

This paper develops a quantum thermodynamics framework accounting for uncertainty in equilibrium states, revealing fundamental limits and irreversibility in work extraction and formation.

Contribution

It introduces a set-based approach to uncertain equilibrium, proves a no-go theorem on resource conversion, and characterizes work costs with new entropic measures.

Findings

Uncertainty in equilibrium states limits thermodynamic resource conversion.

Work extraction and formation are characterized by min- and max-relative entropies.

Phenomena analogous to bound entanglement occur under equilibrium uncertainty.

Abstract

The resource-theoretic approach to quantum thermodynamics assumes complete knowledge of the thermal equilibrium against which thermodynamic resources are defined. In practice, however, this state is determined by the system Hamiltonian and the bath temperature, neither of which is known with perfect precision. We develop a framework in which the equilibrium reference is specified by a set of candidate states reflecting this uncertainty. Under a generic geometric condition, we prove a no-go theorem that sharply limits athermality ``purification'': conversion from an uncertain athermality resource to a definite target is either trivial or impossible, with no room for tradeoff. We then introduce two complementary battery models: a clean battery with a precisely known equilibrium state and a dirty battery with an uncertain one. For both models, we derive exact one-shot entropic characterizations of work extraction and work of formation in terms of standard min- and max-relative entropies and new subspace-constrained variants. In the asymptotic regime, both models exhibit a strong form of thermodynamic irreversibility. In particular, we give a simple and explicit example in which, in the clean-battery model, work is required to form a state but no work can be extracted from it, in direct analogy with bound entanglement, whereas in the dirty-battery model, work can be extracted but formation requires infinite work cost. These phenomena persist even under arbitrarily small uncertainty, showing that equilibrium uncertainty is not a minor perturbation of the standard theory but a qualitatively new ingredient that reshapes the fundamental limits of thermodynamic resource interconversion.