We present measurements of the $E$-mode ($EE$) polarization power spectrum and temperature-$E$-mode ($TE$) cross-power spectrum of the cosmic microwave background using data collected by SPT-3G, the latest instrument installed on the South Pole Telescope. This analysis uses observations of a $1500{\mathrm{deg}}^2$ region at 95, 150, and 220 GHz taken over a four-month period in 2018. We report binned values of the $EE$ and $TE$ power spectra over the angular multipole range $300\le \ell <3000$, using the multifrequency data to construct six semi-independent estimates of each power spectrum and their minimum-variance combination. These measurements improve upon the previous results of SPTpol across the multipole ranges $300\le \ell \le 1400$ for $EE$ and $300\le \ell \le 1700$ for $TE$, resulting in constraints on cosmological parameters comparable to those from other current leading ground-based experiments. We find that the SPT-3G data set is well fit by a $\mathrm{\Lambda }\mathrm{CDM}$ cosmological model with parameter constraints consistent with those from Planck and SPTpol data. From SPT-3G data alone, we find $H_0=68.8\pm 1.5\mathrm{km}{\mathrm{s}}^{-1}{\mathrm{Mpc}}^{-1}$ and ${\sigma }_8=0.789\pm 0.016$, with a gravitational lensing amplitude consistent with the $\mathrm{\Lambda }\mathrm{CDM}$ prediction ($A_L=0.98\pm 0.12$). We combine the SPT-3G and the Planck data sets and obtain joint constraints on the $\mathrm{\Lambda }\mathrm{CDM}$ model. The volume of the 68% confidence region in six-dimensional $\mathrm{\Lambda }\mathrm{CDM}$ parameter space is reduced by a factor of 1.5 compared to Planck-only constraints, with no significant shifts in central values. We note that the results presented here are obtained from data collected during just half of a typical observing season with only part of the focal plane operable, and that the active detector count has since nearly doubled for observations made with SPT-3G after 2018.

• Received 7 January 2021
• Accepted 4 June 2021

DOI:https://doi.org/10.1103/PhysRevD.104.022003