Wait a sec...
D = sqrt(12800)t^2
= sqrt(6400) * sqrt(2) * t^2
= 80 * sqrt(2) * t^2
dD/dt = 160 * sqrt(2) * t
Isn't it just an error with your arithmetic?
When quantum encryption is widely used, encryption methods used today will be flawed because of the ability of quantum computers to easily factor very large numbers. Therefore, in that sense, an advantage will be that quantum encryption is the only option! :)
Before reading this, please note that my knowledge of physics at this time is quite poor as I'm only 15.
Time is only measurable when relative to a progression/regression of something. Therefore, the limit to which we can measure time depends on the shortest possible progression/regression...