  After propagating through a random amplifying medium, a squeezed state
commonly shows excess noise above the shot-noise level. Since large noise can
significantly reduce the signal-to-noise ratio, it is detrimental for precision
measurement. To circumvent this problem, we propose a noise-reduction scheme
using wavefront shaping. It is demonstrated that the average output quantum
noise can be effectively suppressed even beyond the shot-noise limit. Both the
decrease on amplification strength and the increase on input squeezing strength
can give rise to a decrease in the suppressed average quantum noise. Our
results not only show the feasibility of manipulating the output quantum noise
of random amplifying media, but also indicate potential applications in quantum
information processing in complex environments, such as, quantum imaging,
quantum communication, and quantum key distribution.
