  Ultracold quantum gases are usually prepared in conservative traps for
quantum simulation experiments. The atomic density inhomogeneity, together with
the consequent position-dependent energy and time scales of cold atoms in
traditional harmonic traps, makes it difficult to manipulate and detect the
sample at a better level. These problems are partially solved by optical box
traps of blue-detuned hollow beams. However, generating a high-quality hollow
beam with high light efficiency for the box trap is challenging. Here, we
present a scheme that combines the fixed optics, including axicons and prisms,
to pre-shape a Gaussian beam into a hollow beam, with a digital micromirror
device (DMD) to improve the quality of the hollow beam further, providing a
nearly ideal optical potential of various shapes for preparing highly
homogeneous cold atoms. The highest power-law exponent of potential walls can
reach a value over 100, and the light efficiency from a Gaussian to a hollow
beam is also improved compared to direct optical shaping by a mask or a DMD.
Combined with a one-dimensional optical lattice, a nearly ideal two-dimensional
uniform quantum gas with different geometrical boundaries can be prepared for
exploring quantum many-body physics to an unprecedented level.
