  A quantum critical (QC) fluid exhibits universal subleading corrections to
the area law of its entanglement entropies. In two dimensions when the
partition involves a corner of angle $\theta$, the subleading term is
logarithmic with coefficient $a_\alpha(\theta)$ for the $\alpha$-R\'enyi
entropy. In the smooth limit $\theta\!\to\!\pi$, $a_1(\theta)$ yields the
central charge of the stress tensor when the QC point is described by a
conformal field theory (CFT). For general R\'enyi indices and angles,
$a_\alpha(\theta)$ is richer and few general results exist. We study
$a_\alpha(\theta)$ focusing on two benchmark CFTs, the free Dirac fermion and
boson. We perform numerical lattice calculations to obtain high precision
results in $\theta,\alpha$ regimes hitherto unexplored. We derive field theory
estimates for $a_\alpha(\theta)$, including new exact results, and demonstrate
an excellent quantitative match with our numerical calculations. We also
develop and test strong lower bounds, which apply to both free and interacting
QC systems. Finally, we comment on the near collapse of $a_\alpha(\theta)$ for
various theories, including interacting $O(N)$ models.
