The curves of a given colour all emerge from the horizontal dashed line drawn for that same colour; these denote the infinitely degenerate free Landau level energies ($\omega_0 = 0$), while the labelled curves of the same colour indicate how the degeneracy is broken with increasing confinement (increasing $\omega_0$). It is clear from those levels drawn here that the confinement plays a more important role for negative values of $\ell$ and increasing values of $| \ell |$.[]{data-label="fock_darwin_fm"}](fig3fd-parab.pdf)

Note that we could include all negative $\ell$ states, and these would rise even more than those shown as the confinement potential becomes stiffer. But at the far left of Fig. \[fock\_darwin\_fm\] ($\omega_0 \rightarrow 0$), we approach the free space limit, where the levels all become degenerate (this limit is indicated by the dashed horizontal lines).

[The Landau Gauge]{}
====================

Later on we will illustrate explicitly that correct gauge-invariant properties are obtained for various gauge choices. Here we will not demonstrate this explicitly, but instead point out that differences are apparent in the free space case, and what the root causes for these differences are. We therefore proceed in this section with the Landau gauge discussed in the Introduction, ${\vec{\bf A}}_1 = xB 