 Furthermore, there are interesting numerical results on quantum interference in quantized classical billiards (Casati 2005). Consider a double slit with the source enclosed in a two-dimensional wave resonator with the shape of a classical billiard. Adjust the Gaussian wave packet’s initial average energy to be one 1600th of an excited state of the quantized billiard and send it toward the double slit opening of the resonator. Let the slit width be three De Broglie wavelengths, and suppose that the wave packet is sharply peaked in momentum so that its spatial spread, by the Heisenberg relations, is the width of the resonator. If the shape of the resonator corresponds to a classical chaotic billiard, then there is almost no quantum interference. In the classical case, the multiply reflected waves would become randomized in phase. On the other hand, if the shape of the resonator corresponds to a classical regular billiard, then the well-known interference patterns emerge. So depending on whether the classical billiard is chaotic or not determines whether the quantized quantum analogue exhibits interference. 