The energy spectrum of the QD system without (a) and with (b) photon cavity versus the plunger-gate voltage U_pg including zero-electron states (0ES, golden diamonds), one-electron states (1ES, blue rectangles), and two-electron states (2ES, red dots). The chemical potentials are μ_L = 1.2 meV and μ_R = 1.1 meV (black). The SE state in the bias window is almost doubly degenerate due to the small Zeeman energy.