As you can imagine, though, it’s hard to build a chip that’s capable of switching on and off one trillion times per second. That seems to be the main breakthrough here: DARPA, working with Northrop Grumann, has built a tenstage monolithic amplifier using fairly standard CMOS processes. Exact details aren’t yet available, but it seems plausible that the chip could be fabricated out of indium phosphide, which is capable of switching at much higher frequencies (and at higher power levels) than common semiconductors.