Квантовая механика

# Каков физический механизм в квантовом компьютере? Крис Бевис технолог, физик и системный инженер
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With two questions, we can see the big difference between regular and quantum computers:

What is 2 + 2?

• Regular computer: Easy. 2 + 2 = 2 + 1 + 1 = 3 + 1 = 4. Done.
• Quantum computers: Hmm. Do you want this done quickly? HMMM. I’m 90% sure it’s 4. But maybe it’s 3? Give me some more time….. Yeah, I’m 98% sure it’s 4.

What are the factors of 91?

• Regular computer: Well, 91 divided by 2 is 45.5, so 2 is not a factor. 91 divided by 3 is 30.3, so 3 is not a factor. ……91 divided by x is y.zzzz, so x is not a factor…….. 91 divided by 7 is 13, so 7 and 13 are factors. Hurray!
• Quantum computer: Hmm. I’m 90% sure they’re 7 and 13. Can I stop?

What’s going on here? How can quantum computers be so bad at easy math and so good at hard math?

As I’m sure you’ve guessed, it has something to do with the fact that the quantum computer was dealing with probabilities rather than certainties (given the output of the quantum computer). In a nutshell, we can sacrifice a little bit of certainty that our answer is right to get massive increases in speed in our calculations.

Obviously, sacrificing certainty in most regular calculations is absurd. No one wants their calculator to give 5 as the answer to “what’s 2 + 2?” even if it’s just a small percentage of the time.

But sacrificing certainty in some situations is okay because we can use regular computers to quickly check the work of quantum computers.

Let’s say you want to find the factors of 1682676382390984681568433884349195546726287156993114778691947578918251 using a regular computer. You can’t. I know the factors, and you never will. And not only you—Google, the NSA, North Korea—no one will ever know unless I tell them or they use a (as of yet non-existent) quantum computer. Normal computers are (and will forever be) just too slow.

Я уверен, что вам было бы очень полезно знать, что есть 50% -ная вероятность того, что одним из факторов является 1299458847573889395843. Может быть, это на самом деле не фактор (это не так), но проверка предполагаемых факторов очень проста для обычного компьютера. Мы используем квантовые компьютеры, чтобы угадать, и обычные компьютеры, чтобы проверить.

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