Comment on "Entropic Costs of Extracting Classical Ticks from a Quantum Clock"

TL;DR

This paper critically examines a recent quantum clock implementation, arguing it exhibits classical behavior and misinterprets thermodynamic costs, thus questioning its validity as a true quantum timekeeping device.

Contribution

It provides a detailed critique of the original quantum clock proposal, clarifying fundamental issues in its behavior and thermodynamic analysis.

Findings

The quantum clock shows only classical behavior without intrinsic temporal correlations.

Thermodynamic analysis conflates engineering dissipation with fundamental quantum costs.

The clock is not sufficient for accurate time measurement as a true quantum clock.

Abstract

A recent Letter by Wadhia et al. reports a realization of a quantum clock using a double quantum dot (DQD) [Phys. Rev. Lett. 135, 200407 (2005)]. This Comment identifies two fundamental issues: (I) the claimed ``quantum clock" exhibits only classical behavior and lacks intrinsic temporal correlations between ticks; it is not sufficient for accurate time as a good clock. (II) the thermodynamic analysis misassigns entropy production and conflates amplification with measurement; the reported combined entropy is an engineering dissipation, not a fundamental cost of quantum timekeeping.