Precise Determination of the Energy Levels of the Anharmonic Oscillator from the Quantization of the Angle Variable
Using an ansatz motivated by the classical form of $e^{i\phi}$, where $\phi$ is the angle variable, we construct operators which satisfy the commutation relations of the creation-annihilation operators for the anharmonic oscillator. The matrix elements of these operators can be expressed in terms of {\it entire} functions in the position complex plane. These functions provide solutions of the Ricatti equation associated with the time-independent Schr\"odinger equation. We relate the normalizability of the eigenstates to the global properties of the flows of this equation. These exact results yield approximations which complement the WKB approximation and allow an arbitrarily precise determination of the energy levels. We give numerical results for the first 10 levels with 30 digits. We address the question of the quantum integrability of the system.