Based on the equality of Helmholtz equation and stationary state Schrdinger equation, focalizing plane wave is just the transformation of state function of a photonic from coordinate representation to momentum representation. However, as a result of limited aperture size, the state function in the momentum space could not be reconstructed exactly, which leads to the quantum precision limits of alignment. Under the conditions of quantum limits, the precision is approximately 26% of the diffraction limited angle. It depends on the aperture size only and is irrespective to the focal length. The centroid method on the focal plane could only reach the precision close to the diffraction limited angle. The root mean square of remained errors is still 3.24 times of the quantum limits.