Classicality of the heat produced by quantum measurements

TL;DR

This paper explores the thermodynamic aspects of quantum measurements, demonstrating that heat associated with measurement outcomes is classical when the pointer observable commutes with the Hamiltonian, linking quantum measurement to classical thermodynamics.

Contribution

It models quantum measurement as a thermodynamic process and shows that classical heat uncertainty arises only when the pointer observable commutes with the Hamiltonian.

Findings

Heat uncertainty is classical if the pointer observable commutes with the Hamiltonian.

Measurement stability requires the pointer observable to be a conserved quantity.

The work done during measurement is the change in internal energy due to unitary coupling.

Abstract

Quantum measurement is ultimately a physical process, resulting from an interaction between the measured system and a measuring apparatus. Considering the physical process of measurement within a thermodynamic context naturally raises the following question: How can the work and heat be interpreted? In the present paper we model the measurement process for an arbitrary discrete observable as a measurement scheme. Here the system to be measured is first unitarily coupled with an apparatus and subsequently the compound system is objectified with respect to a pointer observable, thus producing definite measurement outcomes. The work can therefore be interpreted as the change in internal energy of the compound system due to the unitary coupling. By the first law of thermodynamics, the heat is the subsequent change in internal energy of this compound due to pointer objectification. We argue that the apparatus serves as a stable record for the measurement outcomes only if the pointer observable commutes with the Hamiltonian and show that such commutativity implies that the uncertainty of heat will necessarily be classical.