You wouldn't want a quantum computer for everyday computing. They're good at performing very specific types of calculations for research, not running applications.

Because they'd be much bigger and much, much more expensive. And because they don't run as stably as conventional ones. Yet.

We, as a species, have basically failed to build a single one quantum computer that does anything. So... that's why they're not everything yet. It's because there are currently approximately zero.

And the few there kind of are are massive and requires liquid helium to cool them to ungodly cold temperatures. And even then they don't do much, besides allow researchers to test stuff.

Because running a quantum computer is horribly expensive. And pointless, as all they seem to be able to run are some quantum computer benchmarks. I still have to see one solving a serious real world computation.

Actually, I personally doubt they will ever reach that point.

they don't really know if they work yet. its research level.

Most buzz about quantum computers is how they might be able to break traditional encryption algorithms by fast defactorisation of very big numbers. Though they still owe us proof, that this actually works.

There is this paper, which compares the "big" achievements in quantum defactorisation with a (not really) trained dog. Basically every of these achievements cheated with the prior knowledge of the factors or have chosen convenient numbers, while still being worlds away from common key sizes (like 2048 or 4096 bit).

Real usage for quantum cpmputers will probably still take quite a while to manifest.

I upgraded all of my devices to quantum awhile back. A lot of people like to hold off until the bugs are worked out, but I've always been an early adopter.

They need to be cooled to absolute zero. The hardware to do that weighs a couple thousand pounds, and needs a truckload of liquid helium. There's no real way quantum computers will ever be portable, or even home units.

1. we just learned how to make them fairly recently
2. expensive to build
3. expensive to run
4. fucking massive if powerful enough to be useful

A lot of people have already mentioned that they are too large and expensive for consumer devices. They also need to be cooled to temperatures very close to absolute zero (using liquid helium) for the superconductors, which adds additional bulk and power draw.

These quantum computers would also require a different architecture that isn't supported by the majority of software and OSs, since they work very differently to standard non-quantum chips. Think how RISC-V isn't very well supported too well right now, and it's much worse than that since the logic gates needed for computation, storage, etc. need to be rewritten entirely due to the use of qubits over bits! Aside for some very specific research bits, there is nearly nothing that can currently run on a quantum computer.

As of right now, even the largest quantum computers only has a few hundreds, maybe a few thousand, qubits, which isn't enough processing power for running a regular desktop OS and consumer applications, even if everything was magically ported to quantum land. Not only that, major hurdle right now is reducing environmental interference from affecting the qubits, meaning there are currently high error rates, i.e. the qubits do not behave.