  Accurate time transfer has become a crucial issue for future space
experiments which require increasing resolution over large distances. In 2008,
a scheme combining homodyne detection and mode-locked femtosecond lasers was
proposed that leads to a potential timing precision reaching the yoctosecond
range; with a multimode quantum frequency comb as the input field, the sub-shot
noise measurement for the time transfer can further improve the timing
precision. Based on this scheme and applying the multimode squeezing frequency
comb that was measured to have a phase quadrature quantum noise reduction of
1.5 dB at the analyzing frequency 2MHz, the measurable timing fluctuation was
reduced from a shot-noise limited value of 8.9E-23s to 7.5E-23s. To our
knowledge, this is the first experimental demonstration of the time transfer
measurement that achieves a precision beyond the standard quantum limit (SQL).
