Subhash Kak - Quantum Supremacy Is Unlikely, Scientist Says

I don't know if this is a good thing or bad thing. Quantum computers seemed to be so powerful I thought they mignt be dangerous, on the other hand, they may have saved a lot of power - which would have be great for cryptocurrencies. 

Because they work on quantum probability, it seems you can never be sure how it's going to go. 

Google announced this fall to much fanfare that it had demonstrated "quantum supremacy" — that is, it performed a specific quantum computation far faster than the best classical computers could achieve. IBM promptly critiqued the claim, saying that its own classical supercomputer could perform the computation at nearly the same speed with far greater fidelity and, therefore, the Google announcement should be taken "with a large dose of skepticism."

This wasn't the first time someone cast doubt on quantum computing. Last year, Michel Dyakonov, a theoretical physicist at the University of Montpellier in France, offered a slew of technical reasons why practical quantum supercomputers will never be built in an article in IEEE Spectrum, the flagship journal of electrical and computer engineering.

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Quantum Supremacy Is Unlikely, Scientist Says