[javajosh]

The most sensational, and arguably most valuable, use is breaking hard encryption, so QC has "nation state STEM/security funding" written all over it. Even if it's 1% likely to be used in this way, it makes sense for wealthy nations to spend on it. But yeah, it's not the same story as for the IC boom.

>Is there anything even a tiny QC can do better, faster, and cheaper than a classical computer?

This is a really good question, and I don't know the answer. If I were to try, I'd focus on QC efficient algorithms, and what you can do with that in an application. So, in your system a QC is a magic box that takes an O(n^2) algo and makes it O(n), say. But for ordinary humans, n is very small, so this won't matter. I don't think there is mundane problem, e.g. one dealing with ordinary productivity, that a QC can do better than classical. It's shaping up to be a nation-state funded capital intensive information superweapon against private communication. And you know what? Maybe if you can maintain the infrastructure and staff to build one, you deserve to have it! It's especially untroubling if it's capacity is limited, like being able to read 10 2048-bit RSA encrypted messages per day. That's a superpower, but a very limited and expensive one, which I am fine with.

[AlexCoventry]

> The most sensational, and arguably most valuable, use is breaking hard encryption, so QC has "nation state STEM/security funding"

Large-scale electronic computers were first developed for exactly the same purpose, during WWII. The first commercial computers weren't available until a few years after the war, about five years after Colossus.

[javajosh]

Indeed, and it's fun to look at the remarkable differences, which are usually more visible in these early stages of development. It gets to the very heart of what "state" is; the beginning of computation really goes back further, to automata and Charles Babbage, where state is encoded into the position of a cog, and decoded by looking at the cog.

For quantum computing, state is written into the wave function of an isolated particle, which is entangled with other isolated particles such that you can perform a read and get something useful out of it. (TBH I'm a little confused about how QC works at the physical level, because it seems like your program could require different patterns of entanglement, but AFAIK the pattern of qubit entanglement is determined by the hardware setup, and cannot be modified at runtime. Maybe there is a generally reusable "shape" that can be interacted with, cleared, setup for a new computation, etc by poking at the particles in some specific order. It's probably a really nice problem for physics folks who feared they'd never get to use their QM classes.)