Figure 4.

First four light–matter correlated eigenvalues in the Coulomb gauge with (blue, solid) and without (red, dashed) the diamagnetic ²(r) contribution for the Rydberg-type weakly bound hydrogen model (same parameters as Figure 3). Disregarding the quadratic (diamagnetic) term omits the diamagnetic shift that leads to accurate agreement between the two gauges. The inset magnifies the same region as in Figure 3. Recall that the diamagnetic contribution attains increasing impact as the frequency decreases and the amount of polarizable matter available increases.