Poorly.

Slowly.

At extreme low temperatures, where thermal energy and electrical charge behave a bit differently.

>Several hardware companies, such as Google, Honeywell, IBM, and Intel, have built gate model quantum computers, that are now available in the marketplace. These devices must function at very low temperatures, and require expensive refrigeration technology. It turns out that it is very challenging to build reliable qubits, and very difficult to incorporate them into chips. All of these companies are presently working to scale up their machines.

It has been a largely theoretical math-physics construct for much of its existence, first proposed 1980 & 1981. Every time it goes another step further into being physically realized, people celebrate, but we're still in the 1940's or earlier as far as the progress of conventional digital computing.

A quantum computing algorithm is a highly specialized arrangement of hardware, and the unit parts don't rapidly generalize to other tasks like digital computing does. Only certain tasks are amenable at all to quantum algorithms being developed for them. If we can find one task ("Solving a specific encryption algorithm with a specific number of bits key length") that it's well-suited for, we could in theory do it incomparably faster than digital computers ever could (eg "Solve the puzzle in 2^64 guesses instead of 2^128 guesses, which would take longer than the universe has existed"). This point, where it's indisputable that quantum computing is faster for a specific task, is termed "quantum supremacy", and it's part of proving that you have a working quantum computer, whatever's inside the black box. We're starting to get to the point where quantum supremacy is arguably relevant for real physical devices, though not yet to the point that it's reshaping our world for even one practical computing task. As far as I can tell, everyone expects that first task to be breaking conventional encryption algorithms, which will then give way to post-quantum encryption algorithms which work by principles that quantum algorithms can't be applied as well to.