[en] The field of optics has been broadered by the recent discovery of new quantum sources of light, such as antibunched and squeezed light from nonlinear processes such as parametric down-conversion. The experiments described in this article are being undertaken at various locations world-wide and lie outside the well understood domain of classical mechanics. These studies of the uniquely quantum nature of light are fundamentally important to our understanding of its nature. Surprising and innovative applications in areas such as espionage are suggested. (UK)