Could a quantum computer perform the tasks of a regular computer?

In summary, a quantum computer can execute the tasks of an ordinary pc and an ordinary pc can execute all tasks of a quantum computer. The difference is that the outcome of a quantum computation is a superposition of multiple outcomes, which can be broken by measurement.
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box
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I heard one of the problems with quantum computers is there is not a certin output for each input, meaning there is some randomness in their computations. Can this randomness some how be reduced until it becomes negligible? My question is basicly can a quantum computer perform most of the tasks a regular computer can only much faster? Or are there only certin tasks it could perform that would allow some randomness?
 
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of course on paper a quantum computer could precisely model any physical system- including any form of classical computer-but the meltdown problem is the monkey-in-the-wrench as it where- but this is an engineering challenge and many solutions are being proposed-

http://arxiv.org/abs/quant-ph/0502050
 
  • #3
box said:
I heard one of the problems with quantum computers is there is not a certin output for each input, meaning there is some randomness in their computations. Can this randomness some how be reduced until it becomes negligible? My question is basicly can a quantum computer perform most of the tasks a regular computer can only much faster? Or are there only certin tasks it could perform that would allow some randomness?

A quantum computer can execute the tasks of an ordinary pc and an ordinary pc can execute all tasks of a quantum computer. The reason is simple if you realize that QM is all about matrices basically. the operations that you need to perform on these matrices (Bra-ket representations) are all 'classical' in nature.

So what is the big difference ?
Well, the thing is that if you, for example, want to compute the output of a function when you give in 1000 x-values, the ordinary computer will need to evaluate the function a 1000 times. The quantum computer can do the job in just one step. The crucial aspect is however that the outcome will be a SUPERPOSITION of |x>|f(x)>...So basically if you want to know the f(x) for the 500th input x-variable you can get the 500th f(x) output. BUT, all the other info will be gone because according to the QM-formalism, the superposition will be broken due to the measurement. Basically, you have no advantage here.

The trick is (and this is the difficult part of quantum computing) to extract the information out of the superposition in an 'indirect' manner by measuring the relative phases of the constituent parts of the superposition. I will refer to Preskill notes on this subject or look for example to Deutsch's Problem, which is quite introductory and easy to understand. In this problem a quantum computer can check whether a function is balanced or not by performing just ONE single measurement. Classically, this is impossible.
You CAN execute this algorithm on a classical pc though, because of the above reasons

marlon
http://www.theory.caltech.edu/people/preskill/
 
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1. Can a quantum computer replace a regular computer?

No, a quantum computer cannot completely replace a regular computer. While quantum computers have the potential to perform certain tasks much faster than regular computers, they are not designed to perform all the functions that a regular computer can. Quantum computers are best suited for solving specific problems that are difficult for regular computers to handle, such as complex mathematical calculations and simulations.

2. How is a quantum computer different from a regular computer?

A quantum computer operates on the principles of quantum mechanics, while a regular computer uses classical physics. This means that a quantum computer can process information in a fundamentally different way, allowing it to solve certain problems more efficiently. Additionally, quantum computers use quantum bits (qubits) instead of classical bits, which can exist in multiple states at once and provide more computing power.

3. Can a quantum computer run all the same programs as a regular computer?

No, a quantum computer cannot run all the same programs as a regular computer. Quantum computers use a different type of programming language and are best suited for solving specific problems that are difficult for regular computers. Regular computers are still necessary for everyday tasks and general computing needs.

4. Will quantum computers make regular computers obsolete?

It is unlikely that quantum computers will make regular computers obsolete. While quantum computers have the potential to outperform regular computers in certain tasks, they are not designed to handle all types of computing needs. Additionally, the development and use of quantum computers is still in its early stages and it will likely take time for them to become widely available and integrated into everyday use.

5. Are there any limitations to what a quantum computer can do?

Yes, there are limitations to what a quantum computer can do. While quantum computers are incredibly powerful for certain tasks, they are not able to handle all types of computing needs. They are still limited by the laws of quantum mechanics and are best suited for solving specific problems that are difficult for regular computers to handle. Additionally, the development and use of quantum computers is still in its early stages and there are still challenges to overcome in order to make them more practical and widespread.

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