  The formation of bars in disk galaxies is a tracer of the dynamical maturity
of the population. Previous studies have found that the incidence of bars in
disks decreases from the local Universe to z ~ 1, and by z > 1 simulations
predict that bar features in dynamically mature disks should be extremely rare.
Here we report the discovery of strong barred structures in massive disk
galaxies at z ~ 1.5 in deep rest-frame optical images from CANDELS. From within
a sample of 876 disk galaxies identified by visual classification in Galaxy
Zoo, we identify 123 barred galaxies. Selecting a sub-sample within the same
region of the evolving galaxy luminosity function (brighter than L*), we find
that the bar fraction across the redshift range 0.5< z < 2 (f_bar = 10.7 +6.3
-3.5% after correcting for incompleteness) does not significantly evolve. We
discuss the implications of this discovery in the context of existing
simulations and our current understanding of the way disk galaxies have evolved
over the last 11 billion years.
