## 1. Introdcution

## 2. Carnot Engine at Maximal Power

## 3. Endoreversible Otto Cycle

#### 3.1. Isentropic Compression

#### 3.2. Isochoric Heating

#### 3.3. Isentropic Expansion

#### 3.4. Isochoric Cooling

## 4. Classical Harmonic Engine

## 5. Quantum Harmonic Engine

## 6. Concluding Remarks

## Funding

## Acknowledgments

## Conflicts of Interest

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**Figure 1.**Efficiency of the endoreversible Otto cycle at maximal power (red, solid line), together with the Curzon–Ahlborn efficiency (purple, dashed line) and the Carnot efficiency (blue, dotted line) in the high temperature limit, $\hslash {\omega}_{2}/{k}_{B}{T}_{c}=0.1$. Other parameters are ${\alpha}_{c}=1$, ${\alpha}_{h}=1$, and $\gamma =1$.

**Figure 2.**Efficiency of the endoreversible Otto cycle at maximal power (red, solid line), together with the Curzon–Ahlborn efficiency (purple, dashed line) and the Carnot efficiency (blue, dotted line) in the deep quantum regime, $\hslash {\omega}_{2}/{k}_{B}{T}_{c}=10$. Other parameters are ${\alpha}_{c}=1$, ${\alpha}_{h}=1$, and $\gamma =1$.

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