  The ability to convert quantum states from microwave photons to optical
photons is important for hybrid system approaches to quantum information
processing. In this paper we report the up-conversion of a microwave signal
into the optical telecommunications wavelength band using erbium dopants in a
yttrium orthosilicate crystal via stimulated Raman scattering. The microwaves
were applied to the sample using a 3D copper loop-gap resonator and the
coupling and signal optical fields were single passed. The conversion
efficiency was low, in agreement with a theoretical analysis, but can be
significantly enhanced with an optical resonator.
