Nonetheless, previous studies of atomic reflection by surface carried out with thermal supersonic beams have been limited by its high sensitivity to the surface quality [DW]. Since atomic de Broglie wavelengths of thermal beams (around sub-angstroms) are much smaller than the characteristic surface roughness (usually 100 angstroms), the atoms are classically reflected at the repulsive potential [reference]. Under the classical reflection, atoms are very close to the surface outmost atoms, feeling the local variation of the potential along the surface. Therefore, in order to avoid incoherent reflection caused by surface roughness and adsorbates on the surface, complicated surface-preparation processes like annealing and sputtering are crucial to render surfaces smooth at the atomic-level [8-10]. However, since the solid surface are easily affected by surroundings, ultra high vacuum (~10-12 mbar) are necessary during the whole experiment. Besides, even a perfectly clean surface would, nonetheless, have unexpected surface defects, decreasing reflectivity [ref].
 Therefore, the initial stage of atomic mirrors has been proposed in a way that prevents atom-surface collisions because atom-surface interaction has been known to undermine coherent reflection from the surface [ref--]. For example, the evanescent wave mirror[ref] and the magnetic mirror [ref] use the evanescent wave and the magnetic field applied along the surface, respectively, to prevent atom-surface collisions. The artificial repulsive potentials induced by those field push atoms away from the surface before they collide against it. However, the delicate fabrication process and lithography technique are necessary to construct the magnetic mirror and evanescent wave mirror is only applicable to specific atoms. In addition, such mirrors are difficult to make big in size without compromising accuracy.
 Ultracold atoms (~\(\mu K\)), formed by laser-cooling and trapping techniques, have provided a major breakthrough in atomic mirrors. In  general, the de Broglie wavelength of the ultracold atoms is much larger than that of thermal atoms. Such a large atomic de Broglie wavelength emphasize the wave nature of atoms, giving rise to the quantum mechanical phenomena, e.g.; quantum reflection. For instance, magneto-optically trapped(MOT) metastable neon atoms has led to the first observation of a quantum reflection of the atomic wave from the solid surface [27]. It is noteworthy that their study revealed the possibility of using a bare solid material without any applied field as a decent atomic mirror through the quantum reflection. Driven by such a pioneering research, numerous studies on the quantum reflection from the surface both in theory and experiment have been carried out with various solid materials such as silicon or glass surface and even with structured surfaces [ref]. As a result of such active studies, the solid material is finally found to be the proper atomic mirror which reflectivity can reach 1 at certain conditions. Thus, the creation of ultracold atoms made a significant advance in atomic mirrors.
 As previously stated, the quantum reflection breakthrough in discovery of solid atomic mirror, is a quantum mechanical phenomenon in which a particle is reflected by the attractive part of the atom-surface interaction, also known as Casimir-van der Waals potential. The Casimir-van der Waals potential is given by the equation below: