  Ultra-high-Q optical resonators are being studied across a wide range of
research subjects including quantum information, nonlinear optics, cavity
optomechanics, and telecommunications. Here, we demonstrate a new, resonator
on-a-chip with a record Q factor of 875 million, surpassing even microtoroids.
Significantly, these devices avoid a highly specialized processing step that
has made it difficult to integrate microtoroids with other photonic devices and
to also precisely control their size. Thus, these devices not only set a new
benchmark for Q factor on a chip, but also provide, for the first time, full
compatibility of this important device class with conventional semiconductor
processing. This feature will greatly expand the possible kinds of system on a
chip functions enabled by ultra-high-Q devices.
