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Quantum computers theoretically can prove more powerful than any supercomputer, and now scientists calculate just what quantum computers need to attain such "quantum supremacy," and whether or not Google achieved it with their claims last year.
Superposition lets one qubit perform two calculations at once, and if two qubits are linked through a quantum effect known as entanglement, they can help perform 2^2 or four calculations simultaneously; three qubits, 2^3 or eight calculations; and so on. In principle, a quantum computer with 300 qubits could perform more calculations in an instant than there are atoms in the visible universe.
It remains controversial how many qubits are needed to achieve quantum supremacy over standard computers. Last year, Google claimed to achieve quantum supremacy with just 53 qubits, performing a calculation in 200 seconds that the company estimated would take the world's most powerful supercomputer 10,000 years, but IBM researchers argued in a blog post "that an ideal simulation of the same task can be performed on a classical system in 2.5 days and with far greater fidelity."
To see what quantum supremacy might actually demand, researchers analyzed three different ways quantum circuits that might solve problems conventional computers theoretically find intractable. Instantaneous Quantum Polynomial-Time (IQP) circuits are an especially simple way to connect qubits into quantum circuits. Quantum Approximate Optimization Algorithm (QAOA) circuits are more advanced, using qubits to find good solutions to optimization problems. Finally, boson sampling circuits use photons instead of qubits, analyzing the paths such photons take after interacting with one another.
Assuming these quantum circuits were competing against supercomputers capable of up to a quintillion (1018) floating-point operations per second (FLOPS), the researchers calculated that quantum supremacy could be reached with 208 qubits with IQP circuits, 420 qubits with QAOA circuits and 98 photons with boson sampling circuits.
How Many Qubits Are Needed For Quantum Supremacy?
[Journal Reference]: Quantum Journal
(Score: 3, Interesting) by bradley13 on Friday May 22 2020, @05:11AM
Quantum computing is indeed a different beast. Still, the problems we want to solve remain the same, so it becomes a difference in framing. At least for the foreseeable future, any "real" use of a quantum computer will be as an addition to a classic computer. We offload floating-point operations to the floating-point unit on the processor, and we will offload other operations to the quantum-unit.
The whole argument about quantum supremacy seems ridiculous and artificial. They are trying to perform some calculation, and claiming that a classical computer cannot simulate the quantum solution. Whooopie. Real quantum supremacy will come, when you can hand off a real problem, and the quantum computer can get the same result as a classical computer, but in less time. Example: Find the factors of this ginormous number. When a quantum computer can deliver an answer (and the same answer) faster than a classical computer, then we have quantum supremacy.
Everyone is somebody else's weirdo.