Fig. 1. Electron-positron number vs the chirp parameter in a single oscillating potential well

Fig. 2. Optimal chirp parameter vs fundamental frequency in a single oscillating potential well

Fig. 3. Electron-positron pair number vs fundamental frequency in a single oscillating potential well

Fig. 4. Electron-positron pair number vs time in a single oscillating potential well

Fig. 5. Instantaneous bound states vs time in a single oscillating potential well

Fig. 6. Electron-positron number vs the chirp parameter in combined potential wells

Fig. 7. Optimal chirp parameter vs fundamental frequency in combined potential wells

Fig. 8. Electron-positron number vs fundamental frequency in combined potential wells

Fig. 9. Electron-positron number varies with time in combined potential wells

Fig. 10. Temporal and spatial distribution of the number of electrons created under combined potential wells

Fig. 11. Energy spectra of electrons created in combined potential wells

Fig. 12. Frequency spectra under nonlinear chirp