solanoid valves
if you actually ment microseconds, find it among the other stuff impossible by elementary pysical law (unless not having microscopical dimensions)
Consider moving parts implied with any valve and principial limits in effect here. You probably find the fastest switching valves technically used with electronic fuel injectors. Most are piezo actuated valves, achieving switching speeds in the 50 - 100 µs range. To get any fluid flow with this timing, several 100 Bars of pressure are neccessary.
Regards,
Frank