Double Source Lensing Probing High Redshift Cosmology
  Double source lensing, with two sources lensed by the same foreground galaxy,
involves the distance between each source and the lens and hence is a probe of
the universe away from the observer. The double source distance ratio also
reduces sensitivity to the lens model and has good complementarity with
standard distance probes. We show that using this technique at high redshifts
$z>1$, to be enabled by data from the Euclid satellite and other surveys, can
give insights on dark energy, both in terms of $w_0$-$w_a$ and redshift binned
density. We find a dark energy figure of merit of 245 from combination of 256
double source systems with moderate quality cosmic microwave background and
supernova data. Using instead five redshift bins between $z=1.1$-5, we could
detect the dark energy density out to $z\approx5$, or make measurements ranging
between 31$\sigma$ and 2.5$\sigma$ of its values in the bins.
