“It is hard to get your head around,” concedes Winfried Hensinger. “These are ideas that are fully accepted in physics, but they do seem crazy, especially in what is a fundamentally classical world. This is a theory that underlies everything and yet its somehow more mysterious than magic. This notion, for instance, of being able to be in two places at the same time. It’s all so counter-intuitive.”
Hensinger, professor of quantum technologies at the University of Sussex, UK and head of its Ion Quantum Technology Group, has got beyond his own counter-intuition regarding this brand of physics called quantum mechanics. Even Einstein couldn’t bring himself to believe it. As the renowned physicist Richard Feynman once quipped: “If you think you understand quantum mechanics, you don’t.”
Indeed, Hensinger is one of a select group of scientists taking this strangeness and building something with it. In 2017, he published the first full-scale blueprint for a quantum computer. “The ideas of making some kind of machine out of this [physics] has always fascinated me beyond all belief,” says Hensinger, using, for the lay person at least, the apposite phrase.
“Lots of scientists talk about doing so but doubt it can be done. But I love challenges. Put it this way: when I was a kid I wanted to be the science officer on the Enterprise.” A quantum computer might well sound like something out of Star Trek. The theory behind it is, certainly, bewilderingly otherworldly—even if, as it might one day be proven, it’s actually very much the natural order of things everywhere.
To summarise, and extremely so, if a conventional computer uses bits—streams of electrical or optical pulses representing ones or zeros—quantum computers use qubits, usually sub-atomic particles the likes of electrons or photons. Managing these particles is extremely complicated and delicate. But they have quantum properties—one is called entanglement, another superposition—that means a connected group of them provides hugely more processing power than the usual binary bits.
Qubits, in fact, can represent numerous possible combinations of one and zero at the same time. That’s superposition—the ability to be in multiple states simultaneously. The answer to a calculation is finally revealed when the qubits are measured, at which point they revert to either one or zero.
Entanglement is weirder still. It allows two intertwined qubits to exist in a single quantum state. Changing the state of one of the qubits changes the state of the other in a way that’s predictable. That works even if the paired qubits are a long, long way apart.
That’s why Einstein dubbed it “spooky action at a distance”.
Come up with the right algorithms and these chains of entangled qubits can crunch numbers in a way that leaves any classical computer in the dust. Or, at least, they should. To date we’ve seen a machine with 128 qubits. It’s likely those with thousands of qubits will prove to be the game changers.
“It does all require a certain level of abstraction. You have to be comfortable just looking at the math. And postponing your disbelief,” explains Wim van Dam, a professor in the department of computer science at the University of California, Santa Barbara and, like Hensinger, one of the few helping to make quantum computing a reality.
“The fact is that you can have a very fulfilling life without knowing how quantum physics works. But that’s not because it’s mysterious. It’s a theory that’s 100 years old and extremely well-tested. It’s not vague, like theories of black holes in which there’s a lot of guessing. We understand quantum physics much better than we do relativity theory, for example. There’s nothing cutting edge about it. So quantum computing does make sense.”
There are other misconceptions too. The practical outcome of quantum physics, the quantum computer, is often wrongly imagined to be the kind of machine that will make anything possible, replacing the kind of ‘classical’ computing we’ve had for the last half century.
Rather each machine will more likely offer different capabilities. Nor is one likely to sit on your desk any time soon. Rather, these will be properly big, football field-sized, extremely specialist machines that users will access via the cloud. And users will want to because such machines will operate at speeds many many times faster than any computer to date.
Indeed, it will allow one to make the kind of calculations that would take a classical computer billions of years to complete. That speed will also allow it to do what classical computing cannot—model molecular behaviour to allow the development of new materials and pharmaceuticals, for example, or bring in a new era in cryptography or machine intelligence.
“Right now half the scientists around the world are busy simplifying problems so they can be modelled on conventional computers. But they’re often drastic simplifications. That’s no good if, say, you’re trying to simulate a chemical reaction. You need to think of quantum computing as an entirely new tool with which we can experience nature,” says the boyishly excited Hensinger.
“If you want a family portrait, once you’d have spent a lot of time having it painted. And the result would kind of looked like you. That’s classical computing. Now think of the portrait taken with a digital camera. That’s quantum computing.” The difference is a crucial one because, in many regards, the problems we want to tackle are fast becoming beyond classical computing.
“There was this idea in the computing industry that computing power would improve exponentially every few years, so if what you needed couldn’t be handled by a computer now, it was a reasonable strategy just to wait. But that’s just not working out for some of the questions we want answered,” explains Bob Sutor, vice president of IBM’s quantum-oriented Q Strategy, which already has publicly accessible, experimental five- and 16-qubit systems on the cloud, as well as a commercial 20-qubit system accessible at a price and used by the likes of ExxonMobil and CERN.
“Say you want to know how a caffeine molecule interacts with the human brain. You can simulate that precisely on a quantum computer. The computer is your laboratory. It allows you to compute rather than just hope for discovery.
“We need to work towards a system that’s powerful, stable, sellable, upgradable— the total package,” adds Sutor. “When we have something like that from a consumer perspective, most people won’t even know they’re interacting with a quantum computer. But it may be doing a better job of, for example, investing their money or diagnosing a health issue. They’ll start to see new materials they won’t know were developed thanks to quantum computing.”
Everyone is working towards what’s called quantum supremacy—the threshold moment when, for the first time, a quantum computer solves a problem beyond the capabilities of a classical computer. Some say this will happen within the next few years, even by the end of next year.
“Though it’s a bit like asking when your infant daughter becomes smarter than your dog,” says van Dam. “You know it will happen, but pinpointing the moment will be tricky.”
Certainly building a quantum computer will not be easy. Yes, basic versions already exist and new ones keep getting more powerful. But right now they’re less useful than your laptop. Quantum computing is, in classical computing terms, still back in the 1950s. There are multiple problems to crack. To operate effectively, quantum computers have to be super-cooled to temperatures below that of deep space.
Then there’s the matter of what the boffins call noise—environmental factors such as vibration, temperature or the electro-magnetic waves produced by gadgets like your mobile phone. Since the quantum state is so fragile and prone to so-called decoherence, these noise factors give quantum computers a really bad time. They allow errors to creep in.
Solving this is an area Hensinger is focused on. He’s just developed a system that uses microwaves to hold qubits ‘in place’, replacing the more typical use of lasers, which are a less mature and less stable tech. “It’s another big step towards building a practical machine, but just one of numerous challenges,” he says.
But it’s not just a matter of building the hardware. As Hensinger stresses, there’s a whole host of software problems to work through—the working out of quantum algorithms, for example. “And people are late to that because until a few years ago the work could have seemed like a waste of time,” notes Hensinger. ”The number of people working in this field you can probably count on one hand.”
One of them is van Dam. He started thinking about what would actually drive the hardware 20 years ago, an intriguing thing to do when, as he notes, there wasn’t any hardware at all. “Back then you could think in terms of these fantastical machines,” he says. “Now we’re sitting with people who are asking for the actual algorithms to run real machines. You need to know very specific things about a quantum computer before you can write software for it, so I think we’re really far off from creating some level of operating system for all quantum computers.
“It’s funny but when I was a PhD student the fact that we might one day build a quantum computer wasn’t exciting for me, in the same way that astronomers don’t all get excited about ideas of space travel,” he adds. “Yet the advances over just the last five years have been really surprising. And now I think it would be really cool to have such devices. We now understand what the pieces are. We just have to put them together.”
Indeed, advancing quantum computing is leading to different parties pursuing different methodologies which, initially at least, are likely to overlap— much as, in classical computing, vacuum tubes gave way to transistors and then microchips, each a new contribution to taking the same fundamental idea forward.
Big guns, the likes of IBM and Google, are seeking to build their quantum machines using super-cooled super-conductors—essentially pimped-up versions of existing solid state circuit technology—because they see it as the easiest to scale up. Start-ups the likes of IonQ, in Maryland, US, are seeking to build anew from the atomic level upwards—a ‘trapped ion’ model less easily scaled up, some say, but less prone to other problems.
Rigetti, another start-up, in Berkeley, has worked out how to forcibly reset qubits for re-use some 30 times faster, thus removing valuable latency from the system. Hensinger argues that there is already something akin to the Manhattan Project afoot—the brightest minds working in parallel, devising machines of different capabilities and in different ways but with the same shared goal.
Others see something more like an arms race to win a competitive advantage— to provide what initially will be a scarce resource to profit-seeking companies with the money to buy quantum computing time. “For many companies, if you can use quantum computing to only get a one percent improvement on the answer you’d get today, then that makes for a big difference to the bottom line,” notes Betsy Masiello, vice president for product at Rigetti.
Certainly those start-ups have needed a lot of money and investors expect a return. “A venture capitalist walked into my office and told me that a paper I’d written outlining an architecture for building a quantum computer read like a business plan,” recalls Chris Monroe, the co-founder of IonQ, which pulled together USD22 million in initial funding to develop a cloud-based service it expects to have on the market within five years. And a market will be there.
“It’s a well-used example, but if you have, say, 300 cities and need to map the best route for a salesman to travel between them, well there are millions and millions of possible routes but only one optimum one,” adds Monroe.
“And that’s something a quantum computer could work out that a classical one couldn’t, at least not any time soon. A company like FedEx would love to know the answer. And there are any number of big companies with similar interesting problems interested in working with quantum computers to help them get ahead of the curve. I’d say every company with over 50,000 employees already has someone thinking about this. So is this a race? Oh yeah…”
Adam Bouland is a post-doctoral researcher in quantum computing theory at University of California, Berkeley and a technical adviser to another start-up, QC Ware. He writes papers with titles the likes of Complexity Classification of Two- Qubit Commuting Hamiltonians and, better still, On the Complexity and Verification of Quantum Random Circuit Sampling.
He’s the new generation of quantum computing scientist who will likely live long enough to see it become an everyday reality. But, a little disappointingly, he’s level-headed about the likelihood of the wonders of quantum computing coming soon.
“There’s a lot of hype. This myth that quantum computers will be straight out of science fiction, for example, and magically speed up all of computation, is still widespread,” he says.
“Yes, it’s a matter of time before high-quality quantum computers of a substantial size exist. But we’re really not sure when that will be or exactly how good quantum computers will need to be before they become useful. Supremacy will be a watershed moment. But that’s a watershed we’ve yet to reach and that marks the starting point for potential applications of quantum computers, rather than the finish. There is still serious research to be done before quantum computers become practically relevant. That all said, for me to play even a tiny part in making quantum computing real and useful is very exciting.”
It’s no understatement, after all, to say that—assuming all the many challenges are overcome—quantum computing will be revolutionary, akin perhaps to the invention of movable type, or the steam engine, or, indeed, the classical computer.
“It’s like being involved in the space programme of the 1960s,” says Hensinger. “It is incredibly exciting. You can see why more and more nations are concerned about the importance of not being left behind with quantum computing. From defence to productivity, from our understanding of how the world is to making things that change it, quantum computing is going to have a critical impact on so much.”
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