  This paper provides an alternative approach to the problem of preparing pure
Gaussian states in a linear quantum system. It is shown that any pure Gaussian
state can be generated by a cascade of one-dimensional open quantum harmonic
oscillators, without any direct interaction Hamiltonians between these
oscillators. This is physically advantageous from an experimental point of
view. An example on the preparation of two-mode squeezed states is given to
illustrate the theory.
