Noah Brier | September 25, 2019

Why is this interesting? - The Quantum Supremacy Edition

On quantum computing, quantum supremacy, and the inadequacies of language

Recommended Products

Beyond Weird: Why Everything You Thought You Knew about Quantum Physics Is Different
Beyond Weird: Why Everything You Thought You Knew about Quantum Physics Is Different

A book by science journalist Philip Ball, exploring the challenges in understanding and talking about quantum mechanics.

I recognize that today’s edition about quantum mechanics and computing is slightly longer than usual (and more science-y), but I did my best to keep things as concise as possible. I think this is all legitimately interesting and tried to highlight the bits I believe matter in language that is as jargon-free as possible. As always, thanks for reading. - Noah (NRB)

Noah here. Last week the FT and others reported that Google had reached quantum supremacy. “A paper by Google’s researchers seen by the FT … claimed that their [quantum] processor was able to perform a calculation in three minutes and 20 seconds that would take today’s most advanced classical computer, known as Summit, approximately 10,000 years.” The original piece was followed up Monday with another story in the FT titled “Rivals rubbish Google’s claim of quantum supremacy” that offers an explanation of the technology and the controversy.

Unlike the bits in a digital computer, which register either a 1 or 0, quantum bits — known as qubits — can be both at the same time. Along with another quantum phenomenon known as entanglement, through which qubits can influence others they are not even connected to, this opens the way to systems that can handle massively more complex problems. 

Part of the controversy in the computing world lies in the term quantum supremacy. Coined in 2012 by theoretical physicist John Preskill, it denotes the moment when a system built using the new technology can solve a problem that is, for all practical purposes, impossible for even the most powerful supercomputers to handle. 

Why is this interesting?

First off, why should you care about quantum computers? If they really work at scale (which we’re still far away from), “The exponentially greater calculation power could help identify new chemical compounds to treat intractable diseases, and eliminate traffic snarls by predicting and managing the flow of vehicles.” Put simply, quantum computers can act as a powerful lever to solve previously impossible problems. At the same time, they also have the potential to make some of the digital security we rely on easily breakable, something that freaks a lot of people out and tends to lead headlines.

Back to quantum supremacy, from everything I’ve read about quantum mechanics and computing, you should look at every story with very skeptical eyes. In an excellent Y Combinator interview last year, Scott Aaronson, a computer science professor with a focus on quantum computing, explained the issue succinctly:

The single most common misconception, right, which you find repeated in almost every popular article about the subject that is written says, well, a classical computer is made of bits, and so it can just try each possible solution one by one, but a quantum computer is made of qubits, which can be zero and one at the same time, and this means that if you have 100 qubits, that the quantum computer can explore two to the hundredth power states simultaneously, and then it can just try all the possible answers at once. Well, that is gesturing towards something in the vicinity of the truth, but it’s also very seriously misleading. It leads people to think that quantum computers would have capabilities that actually we don’t think that they would have. This is not even controversial within this field, right. We all know this, but it’s very hard to get the message out. I’ve been trying. Here’s the situation. The central thing that quantum mechanics says about the world is that to each possible state of a physical system, each possible way that it could be when you measure it, you have to assign a number called an amplitude, and amplitudes are related to probabilities. A larger amplitude means you’re more likely to see that outcome, but amplitudes are different from probabilities.

To that end, as soon as I read the original FT story I rushed over to Aaronson’s blog, Shtetl-Optimized, to see if he had written about the new research. As of last week he hadn't, but then last night he posted “Scott’s Supreme Quantum Supremacy FAQ!” which answers all the questions I had (and many I didn’t … and a few I didn’t even understand). He even included the question I had: Should I care about this? (His version: “Isn’t this a big overhyped nothingburger?”)

No. As I put it the other day, it’s not an everythingburger, but it’s certainly at least a somethingburger!

It’s like, have a little respect for the immensity of what we’re talking about here, and for the terrifying engineering that’s needed to make it reality. Before quantum supremacy, by definition, the [quantum computing] skeptics can all laugh to each other that, for all the billions of dollars spent over 20+ years, still no quantum computer has even once been used to solve any problem faster than your laptop could solve it, or at least not in any way that depended on its being a quantum computer. In a post-quantum-supremacy world, that’s no longer the case. A superposition involving 250 or 260 complex numbers has been computationally harnessed, using time and space resources that are minuscule compared to 250 or 260.

So Aaronson’s answer is yes and that’s fine for me. More generally, though, a lot of this brings me back to the challenges in thinking and talking about quantum mechanics generally. It’s a world that seems very foreign to us because it feels like it works so differently than the one we experience and were taught in high school. In his great book Beyond Weird, science journalist Philip Ball attributes this challenge to one of language: 

The notion of wave–particle duality goes back to the earliest days of quantum mechanics, but it is as much an impediment as it is a crutch to our understanding. Einstein expressed it by saying that quantum objects present us with a choice of languages, but it’s too easily forgotten that this is precisely what it is: a struggle to formulate the right words, not a description of the reality behind them. Quantum objects are not sometimes particles and sometimes waves, like a football fan changing her team allegiance according to last week’s results. Quantum objects are what they are, and we have no reason to suppose that ‘what they are’ changes in any meaningful way depending on how we try to look at them. Rather, all we can say is that what we measure sometimes looks like what we would expect to see if we were measuring discrete little ball-like entities, while in other experiments it looks like the behaviour expected of waves of the same kind as those of sound travelling in air, or that wrinkle and swell on the sea surface. So the phrase ‘wave–particle duality’ doesn’t really refer to quantum objects at all, but to the interpretation of experiments – which is to say, to our human-scale view of things.

I know there’s a lot here. So what should you take away? Quantum computers seem to be getting more and more real, but we’re still very far away from the whole world of cryptography falling over because we can all of a sudden solve all the intractable problems. With that said, as quantum technology becomes more of a reality, it will also bring huge challenges in the language we use to describe a world that operates very differently than the Newtonian one we’re used to. Also, watch this video of Philip Ball explaining all this stuff, because he knows way more than I do. (NRB)

Computer of the Day:

The other very cool part about quantum computers is they look absolutely amazing. This particular one is a 50-qubit IBM machine from 2017. (NRB)

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Thanks for reading,

Noah (NRB) & Colin (CJN)

PS - Noah here. I’ve started a new company and we are looking for our first/lead product designer to join the team in Brooklyn. If you are a product designer or know anyone who is great, please share. Dinner’s on me at a restaurant of your choice if you help us find someone.

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