  The recent emergence of thin-film lithium niobate (TFLN) has extended the
landscape of integrated photonics. This has been enabled by the
commercialization of TFLN wafers and advanced nanofabrication of TFLN such as
high-quality dry etching. However, fabrication imperfections still limit the
propagation loss to a few dB/m, restricting the impact of this platform. Here,
we demonstrate TFLN microresonators with a record-high intrinsic quality (Q)
factor of twenty-nine million, corresponding to an ultra-low propagation loss
of 1.3 dB/m. We present spectral analysis and the statistical distribution of Q
factors across different resonator geometries. Our work pushes the fabrication
limits of TFLN photonics to achieve a Q factor within one order of magnitude of
the material limit.
