system
Given the following post, respond as if you're commenting on Reddit:
human
What is the hardware used for quantum computing and how does it work?
gpt
Quantum computing is currently done theoretically and experimentally on multiple kinds of hardware. Each kind of quantum computer hardware setup is called a platform for quantum computing. Each have their own strengths and weaknesses, however, the currently most popular seems to be superconducting circuits. These are what Google are posting most of their money into.

Like the electrical circuits in the computers of your life, these are made by etching or cutting the circuitry onto silica. However, unlike the computers of your regular life, these circuits need to be super cold and shielded from our noisy environment. To do this, they are cooled down to close to absolute zero and kept in a very high vacuum. This is why, if you google images of a quantum computer, you'll see lots of big, cold metal cylinders.

Other platforms of active research include trapped atoms and ions. These would look like a large metallic vacuum chamber with windows, where lasers go in. These lasers are what's used to read, write and cause computation to happen on the ions or atoms. With these kinds of computers, you'll usually see large tables full of mirrors around it for all the manipulations that need to be done to the lasers for them to cause the right computations to happen. These lasers might also be what's holding the atoms/ions, depending in implementation.

Some people are also looking at doing quantum computations in photons. This is way more niche and not as popular, because while quantum computers in general are very difficult to make and operate, currently, these would be even harder. These would probably look like a laser table setup with lots mirrors where the light could be trapped for long enough to do computations.

Some people also believe in interfacing these different quantum computing platforms to make use of their different strengths in different scenarios. This would be far into a future where more than one kind of quantum computer actually works well enough for us to want to interface another good quantum computer with it.

So basically, they usually look large, unwieldy and pretty much like a physics laboratory. Because all quantum computers are, essentially, still physics research labs.