Broken detailed balance and entropy production in completely positive and trace-preserving quantum Brownian motion

We rigorously analyze the nonequilibrium thermodynamic behavior of various formulations of quantum Brownian motion using the framework of stochastic thermodynamics. While the widely used Caldeira-Leggett master equation exhibits desirable thermodynamic features—such as the fulfillment of a detailed balance—it fails to ensure complete positivity. In contrast, several completely positive and trace-preserving extensions turn out to be thermodynamically controversial. We show that such extensions introduce anomalous phase-space structures that violate detailed balance at the steady state, leading to nonvanishing entropy production and spurious nonequilibrium currents lacking a clear physical interpretation. Our results highlight a fundamental tension between quantum consistency and thermodynamic equilibration in open quantum systems.