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Friday, May 22, 2020

Another Take on the Search for Quantum Supremacy

This has come up a few times since last year with claims from major Tech.    IEEE Spectrum looks at the supremacy claim again, intro below and more at the link.  How do we measure real results on real problems of value?

How Many Qubits Are Needed For Quantum Supremacy?
Whether Google achieved quantum supremacy depends on perspective
By Charles Q. Choi  in IEEE Spectrum

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.

Whereas classical computers switch transistors either on or off to symbolize data as ones and zeroes, quantum computers use quantum bits or qubits that, because of the bizarre nature of quantum physics, can be in a state of superposition where they are both 1 and 0 simultaneously.

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 22 or four calculations simultaneously; three qubits, 23 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.”  ... '

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