  An experimental study of the dispersion cancellation occurring in
frequency-entangled photon pairs is presented. The approach uses time-resolved
up conversion of the pairs, which has temporal resolution at the fs level, and
group-delay dispersion sensitivity of $\approx \ 20 \, \mathrm{fs}^2$ under
experimental conditions. The cancellation is demonstrated with dispersion
stronger than $\pm 10^3 \, \mathrm{fs}^2$ in the signal $(-)$ and idler $(+)$
modes. The observations represent the generation, compression, and
characterization of ultrashort biphotons with correlation width as small as 6.8
times the degenerate optical period.
