  Numerous bulk crystalline materials exhibit attractive nonlinear and
luminescent properties for classical and quantum optical applications. A
chip-scale platform for high quality factor optical nanocavities in these
materials will enable new optoelectronic devices and quantum light-matter
interfaces. In this article, photonic crystal nanobeam resonators fabricated
using focused ion beam milling in bulk insulators, such as rare-earth doped
yttrium orthosilicate and yttrium vanadate, are demonstrated. Operation in the
visible, near infrared, and telecom wavelengths with quality factors up to
27,000 and optical mode volumes close to one cubic wavelength is measured.
These devices enable new nanolasers, on-chip quantum optical memories, single
photon sources, and non-linear devices at low photon numbers based on
rare-earth ions. The techniques are also applicable to other luminescent
centers and crystals.
