# Quantum Computer?

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## Main Question or Discussion Point

I have no idea how a quantum computer works. The quantum computer evidently exploits the laws of MQ, and therefore the post could be interesting. There are 2 difficulties, for my comprehension.
The first is that MQ works on a statistical basis, and it is not clear how a quantum system can function as a deterministic machine.

The second difficulty is trivially simple: explain how the quantum computer performs the 1 + 1 operation. Well, thinking about it I came to the following purely speculative conclusions: It is true that the QM works on statistical bases, but as has been said to the point of nausea, it produces results of extreme accuracy. So we can not see how, even in this case, the quantum computer can not behave like a real machine of incredible precision.

In no article I have read it explains how the quantum computer does 1 + 1. In reality we climb on the explanation of entaglement effects, overlap of states etc etc. concluding that the quantum computer is able to handle extremely large numbers, almost as if the quantum computer is unable to perform too simple calculations! So we would have a sort of paradox: the quantum computer in order to work well needs to perform very complex calculations. Given its statistical base, such calculations would be as accurate as complex, to the point that if it did 1 + 1, the result would be wrong for too much simplicity !!

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PeterDonis
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the laws of MQ
What is MQ?

FactChecker
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I have no idea how a quantum computer works. The quantum computer evidently exploits the laws of MQ, and therefore the post could be interesting. There are 2 difficulties, for my comprehension.
The first is that MQ works on a statistical basis, and it is not clear how a quantum system can function as a deterministic machine.
Not necessarily. Quantum computers are very suseptible to any thermal or energy "noise". So there are random disturbances. There are also techniques to correct errors but they use more qbits to get the job done.
The second difficulty is trivially simple: explain how the quantum computer performs the 1 + 1 operation. Well, thinking about it I came to the following purely speculative conclusions: It is true that the QM works on statistical bases, but as has been said to the point of nausea, it produces results of extreme accuracy.
That is wrong. The power of quantum computers is not its accuracy, the power comes from being able to consider large sets of possibilities in a single step. The current number of qbits in most processors is fairly small (IBM: 49, Google: 72). Those are "universal gate" computers (see https://medium.com/quantum-bits/what-s-the-difference-between-quantum-annealing-and-universal-gate-quantum-computers-c5e5099175a1). One exception is the D-Wave computers, which use quantum annealing and have a thousand qbits. (see https://en.wikipedia.org/wiki/D-Wave_Systems)
So we can not see how, even in this case, the quantum computer can not behave like a real machine of incredible precision.

In no article I have read it explains how the quantum computer does 1 + 1.
Simple things (like carrying a binary digit) involve complications that require Fourier transforms to study. So there is no simple explanation. (see http://cds.cern.ch/record/450434/files/0008033.pdf) (This is as far as my knowledge goes, so I can not give more detail)

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Strilanc

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member 648030
Very intersting.
Quirky panel it's not really a user-friendly interface....
If I want to make one plus one, and possibly get two as a result, what should I do?

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member 648030
What is MQ?
Quantum Mechanics , sorry: QM
they are commutative....

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poseidon721
Strilanc
Very intersting.
Quirky panel it's not really a user-friendly interface....
If I want to make one plus one, and possibly get two as a result, what should I do?
You need to encode your two numbers as, say, little endian 2s complement. Then you apply an addition circuit to them. Then you look at the output and interpret it as a little endian 2s complement integer. You can either use the built-in adder gate or use one constructed from controlled-NOT operations.

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member 648030
Thank you. Very interesting... So Quantum Computer say: "one plus one make two" Excellent!

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jedishrfu
Mentor
There’s a recent video by Domain of Science on YouTube that explains the 5 misconceptions of Quantum Computing. It’s also listed in the PF video section.