Relativistic quantum Otto heat engine using a three-level Unruh-DeWitt detector

In this study, we explore a relativistic quantum Otto heat engine with a qutrit as the working substance interacting with a quantum scalar field in curved spacetime. Unlike qubits, which extract work by simply expanding or shrinking a single energy gap, qutrits allow multiple energy gaps to be adjusted independently, enabling more versatile work extraction in the quantum Otto cycle. We derive a general positive work condition in terms of the effective temperature that each pair of energy levels perceives. Moreover, we discuss additional subtleties that are absent when using a qubit, such as the generation of coherence terms in the density matrix due to interactions.