  This article presents the results of two studies of Higgs boson properties
using the $WW^*(\rightarrow e\nu\mu\nu)jj$ final state, based on a dataset
corresponding to 36.1/fb of $\sqrt{s}$=13 TeV proton$-$proton collisions
recorded by the ATLAS experiment at the Large Hadron Collider. The first study
targets Higgs boson production via gluon$-$gluon fusion and constrains the CP
properties of the effective Higgs$-$gluon interaction. Using angular
distributions and the overall rate, a value of $\tan(\alpha) = 0.0 \pm 0.4$
stat. $ \pm 0.3$ syst is obtained for the tangent of the mixing angle for
CP-even and CP-odd contributions. The second study exploits the vector-boson
fusion production mechanism to probe the Higgs boson couplings to
longitudinally and transversely polarised $W$ and $Z$ bosons in both the
production and the decay of the Higgs boson; these couplings have not been
directly constrained previously. The polarisation-dependent coupling-strength
scale factors are defined as the ratios of the measured polarisation-dependent
coupling strengths to those predicted by the Standard Model, and are determined
using rate and kinematic information to be
$a_L=0.91^{+0.10}_{-0.18}$(stat.)$^{+0.09}_{-0.17}$(syst.) and $a_{T}=1.2 \pm
0.4 $(stat.)$ ^{+0.2}_{-0.3} $(syst.). These coupling strengths are translated
into pseudo-observables, resulting in $\kappa_{VV}=
0.91^{+0.10}_{-0.18}$(stat.)$^{+0.09}_{-0.17}$(syst.) and $\epsilon_{VV}
=0.13^{+0.28}_{-0.20}$ (stat.)$^{+0.08}_{-0.10}$(syst.). All results are
consistent with the Standard Model predictions.
