  One hundred years ago, in 1908, Hermann Minkowski completed his proof that
Maxwell's equations are covariant under Lorentz transformations. During this
process, he introduced a four-dimensional space called the Minkowskian space.
In 1949, P. A. M. Dirac showed the Minkowskian space can be handled with the
light-cone coordinate system with squeeze transformations. While the squeeze is
one of the fundamental mathematical operations in optical sciences, it could
serve useful purposes in two-level systems. Some possibilities are considered
in this report. It is shown possible to cross the light-cone boundary in
optical and two-level systems while it is not possible in Einstein's theory of
relativity.
