  Statistical properties of gas absorption in high redshift quasars such as
power spectrum and bispectrum allow one to determine the evolution of structure
over the redshift range 2<z<4. Sloan Digital Sky Survey (SDSS) will measure
around 10,000 quasar spectra in this redshift range and will allow one to
determine the growth factor with a few percent accuracy. This allows one to
extend the studies of dark energy to higher redshift and determine the presence
of dark energy if Omega_de>0.1-0.2 at z>2. In combination with low redshift
studies one can place useful limits on the time evolution of the equation of
state.
