  Parametric amplification of vacuum fluctuations is crucial in modern quantum
optics, enabling the creation of squeezing and entanglement. We demonstrate the
parametric amplification of vacuum fluctuations for matter waves using a spinor
F=2 Rb-87 condensate. Interatomic interactions lead to correlated pair creation
in the m_F= +/- 1 states from an initial unstable m_F=0 condensate, which acts
as a vacuum for m_F unequal 0. Although this pair creation from a pure m_F=0
condensate is ideally triggered by vacuum fluctuations, unavoidable spurious
initial m_F= +/- 1 atoms induce a classical seed which may become the dominant
triggering mechanism. We show that pair creation is insensitive to a classical
seed for sufficiently large magnetic fields, demonstrating the dominant role of
vacuum fluctuations. The presented system thus provides a direct path towards
the generation of non-classical states of matter on the basis of spinor
condensates.
