  We investigate the group-scale environment of 15 luminous quasars (luminosity
$L_{\rm 3000}>10^{46}$ erg s$^{-1}$) from the Cosmic Ultraviolet Baryon Survey
(CUBS) at redshift $z\approx1$. Using the Multi Unit Spectroscopic Explorer
(MUSE) integral field spectrograph on the Very Large Telescope (VLT), we
conduct a deep galaxy redshift survey in the CUBS quasar fields to identify
group members and measure the physical properties of individual galaxies and
galaxy groups. We find that the CUBS quasars reside in diverse environments.
The majority (11 out of 15) of the CUBS quasars reside in overdense
environments with typical halo masses exceeding $10^{13}{\rm M}_{\odot}$, while
the remaining quasars reside in moderate-size galaxy groups. No correlation is
observed between overdensity and redshift, black hole (BH) mass, or luminosity.
Radio-loud quasars (5 out of 15 CUBS quasars) are more likely to be in
overdense environments than their radio-quiet counterparts in the sample,
consistent with the mean trends from previous statistical observations and
clustering analyses. Nonetheless, we also observe radio-loud quasars in
moderate groups and radio-quiet quasars in overdense environments, indicating a
large scatter in the connection between radio properties and environment. We
find that the most UV luminous quasars might be outliers in the stellar
mass-to-halo mass relations or may represent departures from the standard
single-epoch BH relations.
