Understanding the Intricacies of Quantum Computers and Their Limitations

In summary, the conversation is about the difficulties in understanding how a quantum computer works, particularly with regards to its use of statistical bases and its ability to perform simple calculations like 1 + 1. Despite being able to handle extremely large numbers, the accuracy of the results is not guaranteed. However, there are techniques to correct errors. The conversation also mentions the use of Fourier transforms and Quirk's addition circuit to explain the process of adding two numbers on a quantum computer. Finally, the conversation recommends a video by Domain of Science on the misconceptions of quantum computing.
  • #1
member 648030
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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  • #3
CharlesDarwin said:
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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  • #4
CharlesDarwin said:
In no article I have read it explains how the quantum computer does 1 + 1.

Did you try searching for an answer? When I google "How does does a quantum computer do 1+1" I get results from the quantum computing stack exchange such as "How does a quantum computer do basic math at the hardware level?" and even "How do I add 1+1 using a quantum computer?".

The addition circuit is one of the example circuits in Quirk:

addition-circuit.png
 

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  • #5
Very intersting.
Quirky panel it's not really a user-friendly interface...:smile:
If I want to make one plus one, and possibly get two as a result, what should I do?o_O
 
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  • #6
PeterDonis said:
What is MQ?
Quantum Mechanics , sorry: QM
they are commutative...
 
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  • #7
CharlesDarwin said:
Very intersting.
Quirky panel it's not really a user-friendly interface...:smile:
If I want to make one plus one, and possibly get two as a result, what should I do?o_O

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.

one-plus-one.png
 

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  • #8
Thank you. Very interesting... So Quantum Computer say: "one plus one make two" Excellent!
 
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  • #9
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.
 

1. What is a quantum computer?

A quantum computer is a type of computer that uses the principles of quantum mechanics to perform operations. While traditional computers use bits (0s and 1s) to store and process information, quantum computers use quantum bits or qubits, which can represent multiple values simultaneously. This allows quantum computers to solve certain problems much faster than traditional computers.

2. How do quantum computers work?

Quantum computers use the principles of superposition and entanglement to perform operations. Superposition allows qubits to exist in multiple states at the same time, while entanglement links the states of multiple qubits together. This allows quantum computers to process and store large amounts of information simultaneously, leading to faster and more efficient calculations.

3. What are the limitations of quantum computers?

Quantum computers are still in the early stages of development and have several limitations. One major limitation is the high sensitivity of qubits to external disturbances, which can cause errors in calculations. Another limitation is the difficulty in scaling quantum computers to larger sizes due to the challenges in maintaining the delicate quantum states of qubits.

4. What are some potential applications of quantum computers?

Quantum computers have the potential to revolutionize many industries, including finance, healthcare, and cybersecurity. They can be used to solve complex optimization problems, improve drug discovery and development, and enhance data encryption and security. Quantum computers may also have applications in artificial intelligence and machine learning.

5. How can we overcome the limitations of quantum computers?

Researchers are constantly working on ways to overcome the limitations of quantum computers. Some solutions include developing new error correction techniques and improving the stability of qubits. Another approach is to use a hybrid approach, combining the power of quantum and classical computers to overcome the limitations of both. Continued research and development in this field will be crucial in unlocking the full potential of quantum computers.

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