  Upcoming cosmic microwave background (CMB) surveys will soon make the first
detection of the polarized Sunyaev-Zel'dovich effect, the linear polarization
generated by the scattering of CMB photons on the free electrons present in
collapsed objects. Measurement of this polarization along with knowledge of the
electron density of the objects allows a determination of the quadrupolar
temperature anisotropy of the CMB as viewed from the space-time location of the
objects. Maps of these remote temperature quadrupoles have several cosmological
applications. Here we propose a new application: reconstruction of the
cosmological reionization history. We show that with quadrupole measurements
out to redshift 3, constraints on the mean optical depth can be improved by an
order of magnitude beyond the CMB cosmic variance limit.
