  Polarization data will soon provide the best avenue for measurements of the
CMB lensing potential, although it is potentially sensitive to several
instrumental effects including beam asymmetry, polarization angle
uncertainties, sky coverage, as well as analysis choices such as masking. We
derive "bias-hardened" lensing estimators to mitigate these effects, at the
expense of somewhat larger reconstruction noise, and test them numerically on
simulated data. We find that the mean-field bias from masking is significant
for the EE quadratic lensing estimator, however the bias-hardened estimator
combined with filtering techniques can mitigate the mean field. On the other
hand, the EB estimator does not significantly suffer from the mean-field from
the point source masking and survey window function. The contamination from
beam asymmetry and polarization angle uncertainties, however, can generate
mean-field biases for the EB estimator. These can also be mitigated using
bias-hardened estimators, with at most a factor of ~ 3 degradation of noise
level compared to the conventional approach.
