  The coherent electronic transport phenomena through quantum devices is
difficult to observe due to thermal smearing and dephasing, the latter induced
by inelastic scattering by phonons or impurities. In other wave systems, the
temperature and dephasing may not destroy the coherence and can then be used to
observe the underlying wave behaviour of the coherent quantum phenomena. Here,
we observe coherent transmission of mechanical waves through a two-dimensional
elastic Sinai billiard with two waveguides. The flexural-wave transmission
performed by non-contact means, shows the transmission quantization when a new
mode becomes open. In contrast with the quantum counterpart, these measurements
agree with the theoretical predictions of the simplest model at zero
temperature highlighting the universal character of the transmission
fluctuations.
