  We show that observations of high-redshift Ly-alpha emitters (LAEs) have the
potential to provide definitive evidence for reionization in the near future.
Using 200 Mpc radiative transfer simulations, we calculate the effect that
patchy reionization has on the line profile, on the luminosity function, and,
most interestingly, on the clustering of emitters for several realistic models
of reionization. Reionization increases the measured clustering of emitters,
and we show that this enhancement would be essentially impossible to attribute
to anything other than reionization. Our results motivate looking for the
signature of reionization in existing LAE data. We find that for stellar
reionization scenarios the angular correlation function of the 58 LAEs in the
Subaru Deep Field z = 6.6 photometric sample is more consistent with a fully
ionized universe (mean volume ionized fraction x_i = 1) than a universe with
x_i < 0.5 at >2-sigma confidence level. Measurements in the next year on Subaru
will increase their z = 6.6 LAE sample by a factor of five and tighten these
limits. If the clustering signature of reionization is detected in a LAE
survey, a comparison with a Lyman-break or a H-alpha survey in the same field
would confirm the reionization hypothesis. We discuss the optimal LAE survey
specifications for detecting reionization, with reference to upcoming programs.
