Squeezed vacuum field can be amplified or deamplified when it is injected, as
the signal beam, into a phase-sensitive optical parametric amplifier (OPA)
inside an optical cavity. The spectral features of the reflected quantized
signal field are controlled by the relative phase between the injected squeezed
vacuum field and the pump field for the OPA. The experimental results
demonstrate coherent phenomena of OPA in the quantum regime, and show
phase-sensitive manipulations of quantum fluctuations for quantum information
processing.Comment: 4 pages, 3 figures, appear in Phys. Rev. Let