  Quantum metrology utilizes nonclassical states to improve the precision of
measurement devices. In this context, strongly squeezed vacuum states of light
have proven to be a useful resource. They are typically produced by spontaneous
parametric down-conversion, but have not been generated at shorter wavelengths
so far, as suitable nonlinear materials do not exist. Here, we report on the
generation of strongly squeezed vacuum states at 532 nm with 5.5 dB noise
suppression by means of frequency up-conversion from the telecommunication
wavelength of 1550 nm. The up-converted states are employed in a model
Mach-Zehnder interferometer to illustrate their use in quantum metrology.
