Probing Gravitational Lensing of the CMB with SDSS-IV Quasars
  We study the cross-correlation between the Planck CMB lensing convergence map
and the eBOSS quasar overdensity obtained from the Sloan Digital Sky Survey
(SDSS) IV, in the redshift range $0.9 < z < 2.2$. We detect the CMB lensing
convergence-quasar cross power spectrum at $5.4 \sigma$ significance. The cross
power spectrum provides a quasar clustering bias measurement that is expected
to be particularly robust against systematic effects. The redshift distribution
of the quasar sample has a median redshift $z \approx 1.55$, and an effective
redshift about $1.51$. The best fit bias of the quasar sample is $b_q = 2.43
\pm 0.45$, corresponding to a host halo mass of $\log_{10}\left(
\frac{M}{h^{-1} M_\odot} \right) = 12.54^{+0.25}_{-0.36}$. This is broadly
consistent with the previous literature on quasars with a similar redshift
range and selection. Since our constraint on the bias comes from the
cross-correlation between quasars and CMB lensing, we expect it to be robust to
a wide range of possible systematic effects that may contaminate the auto
correlation of quasars. We checked for a number of systematic effects from both
CMB lensing and quasar overdensity, and found that all systematics are
consistent with null within $2 \sigma$. The data is not sensitive to a possible
scale dependence of the bias at present, but we expect that as the number of
quasars increases (in future surveys such as DESI), it is likely that strong
constraints on the scale dependence of the bias can be obtained.
