  Theoretical models of a spin-polarized voltage probe (SPVP) tunnel-coupled to
the helical edge states (HES) of a quantum spin Hall system (QSHS) are studied.
Our first model of the SPVP comprises $N_{P}$ spin-polarized modes (subprobes),
each of which is locally tunnel-coupled to the HES, while the SPVP, as a whole,
is subjected to a self-consistency condition ensuring zero average current on
the probe. We carry out a numerical analysis which shows that the optimal
situation for reading off spin-resolved voltage from the HES depends on the
interplay of the probe-edge tunnel-coupling and the number of modes in the
probe ($N_P$). We further investigate the stability of our findings by
introducing Gaussian fluctuations in {\it{(i)}} the tunnel-coupling between the
subprobes and the HES about a chosen average value and {\it{(ii)}}
spin-polarization of the subprobes about a chosen direction of the net
polarization of SPVP. We also perform a numerical analysis corresponding to the
situation where four such SPVPs are implemented in a self-consistent fashion
across a ferromagnetic barrier on the HES and demonstrate that this model
facilitates the measurements of spin-resolved four-probe voltage drops across
the ferromagnetic barrier. As a second model, we employ the edge state of a
quantum anomalous Hall state (QAHS) as the SPVP which is tunnel-coupled over an
extended region with the HES. A two-dimensional lattice simulation for the
quantum transport of the proposed device setup comprising a junction of QSHS
and QAHS is considered and a feasibility study of using the edge of the QAHS as
an efficient spin-polarized voltage probe is carried out in presence of an
optimal strength of the disorder.
