  Flat band electronic modes in twisted graphene bilayers are responsible for
superconducting and other highly correlated electron-electron phases. Although
some hints were known of a possible connection between the quantum Hall effect
and zero flat band modes, it was not clear how such connection appears. Here
the electronic behavior in twisted bilayer graphene is studied using the chiral
model Hamiltonian. As a result, it is proved that for high-order magic angles,
the zero flat band modes converge into coherent Landau states with a dispersion
$\sigma^2=1/3\alpha$, where $\alpha$ is a coupling parameter that incorporates
the twist angle and energetic scales. Then it is proved that the square of the
hamiltonian, which is a $2\times 2$ matrix operator, turns out to be equivalent
to a two-dimensional quantum harmonic oscillator. The interlayer currents
between graphene's bipartite lattices are identified with the angular momentum
term while the confinement potential is an effective quadratic potential. From
there it is proved a limiting quantization rule for high-order magic angles,
i.e., $\alpha_{m+1}-\alpha_{m}=3/2$ where $m$ is the order of the angle. All
these results are in very good agreement with numerical calculations.
