It's been a while since I listened to a couple of interviews on this. I can't remember who those involved were, but they were super concerned about it. Especially the ability to brute force the security of all other nations that don't yet have it. They essentially said that whatever nation got it first, would basically instantly have the power to completely shut down all other nations' military bases, equipment, etc and to shut down power grids, water services, etc and basically cripple all other nations.
The interviews did discuss all the cool crap it would be able to bring, but how due to people being people, we probably won't get that stuff because we will probably do the above first.
My concern is that the US has several companies, and several universities, working on this, but is Google "Us"? What happens if a company is the first to reach it.
Also, LOL at us spending only $1B annually on this.