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> In theory, a quantum machine with just a few hundred qubits should be able to run calculations that would be inconceivable using traditional hardware. Accord

> In theory, a quantum machine with just a few hundred qubits should be able to run calculations that would be inconceivable using traditional hardware. According to https://en.wikipedia.org/wiki/Timeline_of_quantum_computing https://en.wikipedia.org/wiki/Timeline_of_quantum_computing Google has a 72-qubit system which I would expect to already be game changer if the above quote is true, but have heard about the applications of quantum computing only in the future tense. Does the power of a quantum computer scale linearly with number of qubits? Does the difficulty in manufacturing scale linearly with number of qubits?

positr0n 8y ago
The citation for that line[0] says they are still testing it. From my reading it sounds like they built some hardware, but it doesn't work yet :-) [0]: https://www.sciencenews.org/article/google-moves-toward-quantum-supremacy-72-qubit-computer https://www.sciencenews.org/article/google-moves-toward-quan...
abdullahkhalids 8y ago
In the quote, "few hundred qubits", qubits are logical qubits. Google's 72-qubits are physical qubits. You implement error correction on the physical qubits, after which you are left with a lot fewer logical qubits, to do your actual computation with. > Does the power of a quantum computer scale linearly with number of qubits? It scales linearly with the number of logical qubits, in the same sense the power of a turing machine scales linearly with the size of the tape. Also, for a realistic system of hundreds of qubits, you will need tens of thousands of physical qubits. > Does the difficulty in manufacturing scale linearly with number of qubits? If you want the ability to do entangling operations on any two qubits, however far apart they are physically, the manufacturing difficulty scales quadratically with the number of qubits at least. However, you can choose to only have the ability to do entangling operations on near by qubits, and use swap operations to move the state of the qubits around. This will reduce manufacturing difficulty scaling, but will increase the time of any computation you perform.

positr0n 8y ago

The citation for that line[0] says they are still testing it. From my reading it sounds like they built some hardware, but it doesn't work yet :-) [0]: https://www.sciencenews.org/article/google-moves-toward-quantum-supremacy-72-qubit-computer https://www.sciencenews.org/article/google-moves-toward-quan...

abdullahkhalids 8y ago

In the quote, "few hundred qubits", qubits are logical qubits. Google's 72-qubits are physical qubits. You implement error correction on the physical qubits, after which you are left with a lot fewer logical qubits, to do your actual computation with. > Does the power of a quantum computer scale linearly with number of qubits? It scales linearly with the number of logical qubits, in the same sense the power of a turing machine scales linearly with the size of the tape. Also, for a realistic system of hundreds of qubits, you will need tens of thousands of physical qubits. > Does the difficulty in manufacturing scale linearly with number of qubits? If you want the ability to do entangling operations on any two qubits, however far apart they are physically, the manufacturing difficulty scales quadratically with the number of qubits at least. However, you can choose to only have the ability to do entangling operations on near by qubits, and use swap operations to move the state of the qubits around. This will reduce manufacturing difficulty scaling, but will increase the time of any computation you perform.