  According to Clausius formulation of the second law of thermodynamics, for
any thermal machine withdrawing heats $Q_{1,2}$ from two heat reservoirs at
temperatures $T_{1,2}$, it holds $Q_1/T_1+Q_2/T_2 \leq 0$. Combined with the
observation that the quantity $Q_1+Q_2$ is the work $W$ done by the system,
that inequality tells that only 4 possible operation modes are possible for the
thermal machine, namely heat engine [E], refrigerator [R], thermal accelerator
[A] and heater [H]. We illustrate their emergence in the finite time operation
of a quantum Otto engine realised with a single qubit. We first focus on the
ideal case when isothermal and thermally-insulated strokes are well separated,
and give general results as well as results pertaining to the specific
finite-time Landau-Zener dynamics. We then present realistic results pertaining
to the solid-state experimental implementation proposed by Karimi and Pekola
[Phys. Rev. B \textbf{94} (2016) 184503]. That device is non-adiabatic both in
the quantum mechanical sense and in the thermodynamical sense. Oscillations in
the power extracted from the baths due to coherent LZ tunnelling at too low
temperatures are observed that might hinder the robustness of the operation of
the device against experimental noise on the control parameters.
