Quantum Computing is Going Nowhere

Quantum computing seems like a breakthrough. The basic idea is that while a non-quantum bit must have one of two states, 0 or 1, a quantum bit or qubit can have all sorts of values, especially when you link a lot of them together. Back in 1994 it was demonstrated mathematically that this would make certain computing tasks much faster. The one that caught people's attention was factoring large numbers into primes, because most digital security systems depend on other computers not being able to do that.

People have been trying to build a quantum computer ever since. And they have made some success; why, just last year a team reported that their quantum computer had actually performed a factoring calculation, and done it faster than any standard computer. Cool! But the problem they solved was factoring the number 21 into 3x7. Google made lot of noise in 2019 by proclaiming "quantum supremacy" because they thought their Sycamore machine, with 53 qubits, solved a certain weird problem faster than any conventional computer could. The task was utterly useless, designed to show that the quantum computer was better than regular computers at something. Still, it took a Chinese team less than a year to beat Google's quantum machine at its own weird task. So much for supremacy.

To make a quantum computer work you have to maintain a large number of qubits in a state called superposition. Right now this can be done for less than a hundred qubits, for a fraction of a second, at a temperature close to absolute zero. To solve the kind of high-level problems that non-quantum computer struggle with you would need tens of thousands of qubits. Others say you would need millions, while yet others say billions. And rather than getting easier as you add more qubits, the problems seems to get exponentially more difficult as you add more qubits to the system.

Besides the hardware issues, there are also major questions about the algorithms these computers would use. The famous 1994 aglorithm for factoring large numbers is one of only about a dozen that have ever been proposed for quantum computing. Back in 1994 people expected that hundreds of ways of using quantum computing power would very quickly be found, but that hasn't happened. Instead, we are stuck with just a few, most of them with little real-world value. It seems more and more like quantum computers will always have to be specialized machines.

So right now we are seeing a wave of quantum debunking. German physicist and YouTube star Sabine Hossenfelder is all over this; she recently uploaded her second 20-minute video debunking quantum computing, this one titled The Quantum Hype Bubble is About to Burst. 

But it isn't just her. Quantum computing pioneer Sankar Das Sarma says "Quantum Computing has a Hype Problem." Physicist Mikhail Dyakonov wrote a book titled Will We Ever Have a Quantum Computer? Which gives the answer, 

No, we will never have a quantum computer. Instead, we might have some special task (and outrageously expensive) quantum devices operating at millikelvin temperatures.

The saga of quantum computing is waiting for profound sociological analysis, and some lessons for the future should be learnt from this fascinating adventure.

What bothers these physicists is not the pursuit of quantum computing, but the claims being made about it and the financial corruption those claims may represent. The claims are coming from companies like Google and Microsoft, not to mention a whole raft of startups with multi-billion dollar evaluations. Scott Aaronson wrote back in 2021 that the financial temptations were creating a real moral hazard. Years before he had responded to all talk of "quantum ethics" with jokes, but by 2021:

These days, I really do feel like quantum computing research has become an ethical minefield—but not for any of the reasons mentioned previously. What’s new is that millions of dollars are now potentially available to quantum computing researchers, along with equity, stock options, and whatever else causes “ka-ching” sound effects and bulging eyes with dollar signs. And in many cases, to have a shot at such riches, all an expert needs to do is profess optimism that quantum computing will have revolutionary, world-changing applications and have them soon. Or at least, not object too strongly when others say that.

Just recently he posted another attack piece, titled "Cargo Cult Quantum Factoring." The paper under consideration, he wrote, "is one of the most actively misleading quantum computing papers I’ve seen in 25 years, and I’ve seen … many." (His ellipsis)

I feel the same way about quantum computers as I do about fusion power. These are real technologies that will one day turn out to be very important, but we don't know when that will happen and it might take decades. I have a sense that the billions being thrown at both technologies now are mostly wasted, because we are trying to get ahead of ourselves. We need for physics and engineering to make a lot of general progress in things like magnets and superconduction before we will really be able to do these things. Maybe throwing billions at quantum computing and fusion is one way to get that progress. But that doesn't make it the best way.