  An experiment is proposed that permits the observation of the reduced de
Broglie wavelengths of two and four-photon wave packets using present
technology. It is suggested to use a Mach-Zehnder setup and feed both input
ports with light generated by a single non-degenerate down-conversion source.
The strong quantum correlations of the light in conjunction with
boson-enhancement at the input beam splitter allow to detect a two- and
fourfold decrease in the observed de Broglie wavelength with perfect
visibility. This allows a reduction of the observed de Broglie wavelength below
the wavelength of the source.
