  We study the cross correlation of damped Ly$\alpha$ systems (DLAs) and their
background quasars, using the most updated DLA catalog and the Planck 2018 CMB
lensing convergence field. Our measurement suggests that the DLA bias $b_{\rm
DLA}$ is smaller than $3.1$, corresponding to $\log(M/M_\odot h^{-1})\leq 12.3$
at a confidence of $90\%$. These constraints are broadly consistent with Alonso
et al. (2018) and previous measurements by cross-correlation between DLAs and
the Ly$\alpha$ forest (e.g. Font-Ribera et al. 2012; Perez-Rafols et al. 2018).
Further, our results demonstrate the potential of obtaining a more precise
measurement of the halo mass of high-redshift sources using next generation CMB
experiments with a higher angular resolution. The python-based codes and data
products of our analysis are available at
https://github.com/LittleLin1999/CMB-lensingxDLA.
