Scalar and fermionic Unruh Otto engines

TL;DR

This paper explores quantum heat engines driven by the Unruh effect, analyzing how different couplings of a qubit to scalar and fermionic fields affect work output during an accelerated cycle.

Contribution

It introduces a model of Unruh Otto engines with quadratic and fermionic couplings, revealing new qualitative behaviors in work output compared to linear scalar couplings.

Findings

Quadratic and fermionic couplings lead to distinct work output behaviors.

Explicit acceleration conditions for positive work are derived.

Analytical response functions highlight qualitative differences in engine performance.

Abstract

We investigate the behaviour of quantum heat engines, in which a qubit is put through the quantum equivalent of the Otto cycle and the heat reservoirs are due to the Unruh effect. The qubit is described by an Unruh--DeWitt detector model coupled quadratically to a scalar field and alternately to a fermion field. In the cycle, the qubit undergoes two stages of differing constant acceleration corresponding to thermal contact with a hot and cold reservoir. Explicit conditions are derived on the accelerations required for this cycle to have positive work output. By analytically calculating the detector response functions, we show that the dimensionality of the quadratic and fermionic coupling constants introduces qualitatively different behaviour of the work output from this cycle as compared to the case in which the qubit linearly couples to a scalar field.