A measurement of the Hubble constant from angular diameter distances to
  two gravitational lenses
  The local expansion rate of the Universe is parametrized by the Hubble
constant, $H_0$, the ratio between recession velocity and distance. Different
techniques lead to inconsistent estimates of $H_0$. Observations of Type Ia
supernovae (SNe) can be used to measure $H_0$, but this requires an external
calibrator to convert relative distances to absolute ones. We use the angular
diameter distance to strong gravitational lenses as a suitable calibrator,
which is only weakly sensitive to cosmological assumptions. We determine the
angular diameter distances to two gravitational lenses, $810^{+160}_{-130}$ and
$1230^{+180}_{-150}$~Mpc, at redshifts of $z=0.295$ and $0.6304$. Using these
absolute distances to calibrate 740 previously-measured relative distances to
SNe, we measure the Hubble constant to be $H_0=82.4^{+8.4}_{-8.3} ~{\rm
km\,s^{-1}\,Mpc^{-1}}$.
