# Efficiency at maximum power of a quantum Carnot engine with temperature tunable baths. (arXiv:1710.06565v1 [quant-ph])

We investigate the efficiency at maximum power (EMP) of irreversible quantum

Carnot engines that perform finite-time cycles between two temperature tunable

baths. The temperature form we adopt can be experimentally realized in squeezed

baths in the high temperature limit, which makes our proposal of practical

relevance. Focusing on low dissipation engines, we first generalize the

pervious upper as well as lower bounds for the EMP to temperature tunable cases

in which they are solely determined by a generalized Carnot limit. As an

illustrative example, we then consider a minimal heat engine model with a

two-level spin as the working medium. It mimics a low dissipation engine as

confirmed by finite time thermodynamic optimization results. The so-obtained

EMP, being constrained by the generalized bounds, is well described by a

generalized Curzon- Ahlborn efficiency as consequences of a left/right symmetry

for a rate constant and low dissipations. Intriguing features of this minimal

heat engine under optimal power output are also demonstrated.