What are scientists inputting into a quantum computer and what are they getting out of it? I don’t understand what it’s ‘calculating’?
In: Mathematics
If you think of “regular” computers as machines that do mathematical operations over numbers, you can think of quantum computers as doing “quantum” mathematical operations.
You can ask a regular computer what’s 2+3 and it’ll tell you it’s 5. You can then use that result in your next computation and e.g. multiply it by by 5, then check if the result is an odd number.
A quantum computer can do all that, but it can also perform a type of operation where the result doesn’t need to be known right away. You can tell it that you’re interested in 2+3 but that you don’t need it right now – so the result can be kept in a superposition where it’s “some number between 2 and 10”. If you then multiply it by two, you can do it in a way that preserves the superposition, so it’s now “some number between 4 and 20”.
If at this point, however, you check if it’s odd or not, the quantum computer needs to actually collapse the superposition, i.e. “between 4 and 20” is no longer sufficient to get the answer you need and you need to know the real result. But doing this is no faster than doing it on a regular computer, so this type of work isn’t made better by using a quantum computer!
There are, however, some operations that can be made faster this way – for example, if you had a few dozen numbers you calculated using quantum operations and they are all in superpositions, you could use a type of operation unique to quantum computers where you ask “is any of these numbers odd”. This won’t tell you *which* number is odd – that would still require calculating all of them – but if you at least know none of them are, you’ll at least save some time not checking any. In contrast, a regular computer *must* calculate all of them before it can confidently tell you none of them are odd.
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