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Quantum computing

 


Have I written anything about quantum computing in this blog?  I wrote so much here about so many things it is difficult to keep track. 

Ah, I just completed a survey of posts in the history of this blog that involve quantum mechanics  There is a fair number.  NONE of them address the question on my mind today -- whether humanity's understanding of quantum mechanics is about to set off a jump in our marketable computational power. So ... I will correct that lacuna. 

This could yet be the biggest disruption in the high-tech world since transistors replaced vacuum tubes. 

Existing computers, digital computers, work with a lot of on/off gates. Another way of saying this is that they calculate by “1” and “0.” Either number is called a “bit.” Quantum computers, first discussed theoretically by Richard Feynman and Yuri Manin in the early 1980s, have on/off/both gates. In numerical terms, a datum can still be a 1, or a 0, but can also be superposition of 1 and 0.

In essence, the superposition is a probability wave. When, at some point in the performance of a particular algorithm, the wave is collapsed, the value becomes either 1 or 0: until then, the wave represents the probability that it will be the one or the other when that point arrives. In terms of the cliched image: at some point in the execution of a program, the lid is opened and the “cat” is either alive or dead. Until then, it is both.

Superposition means that qubits store more data than bits, which allows for much greater computing power. Indeed, the difference in degree becomes a difference in kind. As John Loeffler, the managing editor of Interesting Engineering, has put it, a “trillion-year problem” can be reduced to a two- to five-year problem “with a quantum computer, and only with a quantum computer.”

Loeffler -- that is his image above -- wrote about the trillion-year problem five years ago, though. That editorial appeared in 2019. And even then there was a sense that a quantum revolution in engineering was hanging fire. It was a huge revolution that was "just about" to happen, but nobody could quantify just how quick "just about" could be. 

And here we are, five years since Loeffler's hopeful words, and the fire is still hanging. 

Now I've said so here. 

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