What makes quantum computing so difficult to explain?

Quantum computers, you we might have heard, they are uber-magic machines that will quickly cure cancer and global warming by testing all possible answers in different parallel universes. For 15 years, forward in my blog and elsewhere, I argue against this caricaturist view, trying to explain what I see as the most subtle but ironically even more fascinating truth. I approach this as a public service and almost do my moral duty as a quantum computing researcher. Unfortunately, the work feels Sisyphean: The cringeworthy impression on quantum computers has only increased over the years, as corporations and governments have invested billions, and that technology has advanced to programmable devices by 50 qubits that ( in some invented benchmarks) can really give the world’s biggest supercomputers a run for his money. And as in cryptocurrency, machine learning and other fashion fields, with money come scammers.

In the reflective moments, though, I understood. The reality is that even if you eliminated all the bad incentives and greed, quantum computing would still be difficult to explain briefly and honestly without math. As the pioneer of quantum computing Richard Feynman once said about the work of quantum electrodynamics that won him the Nobel Prize, if it were possible to describe it in a few sentences, it would not be worth an Prize. Nobel.

Not that this has stopped people from trying. Since Peter Shor discovered in 1994 that a quantum computer could break most of the encryption that protects Internet transactions, the excitement for technology has been driven by more than just intellectual curiosity. In fact, developments in the field are typically covered as histories of business or technology rather than as those of science.

It would be nice if a business or technology journalist could tell the truth to readers, “Well, there’s all this quantum stuff deep under the hood, but all you need to understand is the bottom line: I physicists are on the verge of building faster computers that will revolutionize everything. ”

The problem is that quantum computers will not revolutionize everything.

Yes, one day they could solve a few specific problems in a few minutes that (we think) will take more time than the age of the universe on classic computers. But there are many other important issues for which most experts think that quantum computers help only modestly, if at all. Also, while Google and others have recently made credible claims that they had achieved invented quantum accelerations, this was only for specific esoteric benchmarks (the ones I have helped to develop). A quantum computer that is large and reliable enough to surpass classical computers in practical applications such as breaking cryptographic codes and simulating chemistry is probably still a long way off.

But how could a programmable computer be faster for only a few problems? Do we know who? And what does even a “big and reliable” quantum computer mean in this context? To answer these questions we must go into the deep things.

Let’s start with quantum mechanics. (What could be more profound?) The concept of superposition is infamously difficult to render in everyday words. So, it’s not surprising that many writers opt for an easy way out: They say that the overlay means “both at once,” so a quantum bit, or qubit, is just a bit that can be “either 0 or 1 at the same time, ”while a little classic may be just one or the other. They go on to say that a quantum computer reaches its speed using qubits to test all possible solutions in overlap — that is, at the same time, or in parallel.

It’s what I think of as the fundamental misstep of the popularization of quantum computing, the one that leads to everything else. From here it’s just a short jump to quantum computing by quickly solving something like this travel salesman problem trying all the possible answers at once – something that almost all experts believe they won’t be able to do.

The thing is, for a computer to be useful, at some point you have to look at it and read an output. But if you look at an equal overlap of all possible answers, the rules of quantum mechanics say that you will only see and read a random answer. And if that’s all you want, you can choose one for yourself.

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