Quantum computers promise to run calculations far beyond the reach of any conventional supercomputer. They might revolutionize the discovery of new materials by making it possible to simulate the behaviour of matter down to the atomic level. Or they could upend cryptography and security by cracking otherwise invincible codes. There is even hope they will supercharge artificial intelligence by crunching through data more efficiently.
Yet only now, after decades of gradual progress, are researchers finally close to building quantum computers powerful enough to do things that conventional computers cannot. It’s a landmark somewhat theatrically dubbed “quantum supremacy.” Google has been leading the charge toward this milestone, while Intel and Microsoft also have significant quantum efforts. And then there are well-funded startups including Rigetti Computing, IonQ, and Quantum Circuits.
However, IBM are leading the pack in the race for useable quantum computing. Starting 50 years ago, the company produced advances in materials science that laid the foundations for the computer revolution. It’s a good time to ask questions: What, if anything, will a quantum computer be good for? And can a practical, reliable one even be built?
IBM” Superconducting Quantum Computing
The IBM machine exploits quantum phenomena that occur in superconducting materials. For instance, sometimes current will flow clockwise and counterclockwise at the same time. IBM’s computer uses superconducting circuits in which two distinct electromagnetic energy states make up a qubit.
The superconducting approach has key advantages. The hardware can be made using well–established manufacturing methods, and a conventional computer can be used to control the system. The qubits in a superconducting circuit are also easier to manipulate and less delicate than individual photons or ions.
Inside IBM’s quantum lab, engineers are working on a version of the computer with 50 qubits. You can run a simulation of a simple quantum computer on a normal computer, but at around 50 qubits it becomes nearly impossible. That means IBM is theoretically approaching the point where a quantum computer can solve problems a classical computer cannot: in other words, quantum supremacy.
At the CES technology event in Las Vegas at the beginning of January, IBM unveiled their latest quantum computer, capable of handling 50 qubits (quantum bits). This breakthrough puts IBM on the cutting edge of quantum computing research, as a 50-qubit machine is so far the largest and most powerful quantum computer ever built.
But as IBM’s researchers will tell you, quantum supremacy is an elusive concept. You would need all 50 qubits to work perfectly, when in reality quantum computers are beset by errors that need to be corrected for. It is also devilishly difficult to maintain qubits for any length of time; they tend to “decohere,” or lose their delicate quantum nature, much as a smoke ring breaks up at the slightest air current. And the more qubits, the harder both challenges become.
“If you had 50 or 100 qubits and they really worked well enough, and were fully error-corrected—you could do unfathomable calculations that can’t be replicated on any classical machine, now or ever,” says Robert Schoelkopf, a Yale professor and founder of a company called Quantum Circuits. “The flip side to quantum computing is that there are exponential ways for it to go wrong.”
Another reason for caution is that it isn’t obvious how useful even a perfectly functioning quantum computer would be. It doesn’t simply speed up any task you throw at it; in fact, for many calculations, it would actually be slower than classical machines. Only a handful of algorithms have so far been devised where a quantum computer would clearly have an edge. And even for those, that edge might be short-lived.
The most famous quantum algorithm, developed by Peter Shor at MIT, is for finding the prime factors of an integer. Many common cryptographic schemes rely on the fact that this is hard for a conventional computer to do. But cryptography could adapt, creating new kinds of codes that don’t rely on factorisation.
This is why, even as they near the 50-qubit milestone, IBM’s own researchers are keen to dispel the hype around it. At a table in the hallway that looks out onto the lush lawn outside, I encountered Jay Gambetta, a tall, easygoing Australian who researches quantum algorithms and potential applications for IBM’s hardware. “We’re at this unique stage,” he said, choosing his words with care. “We have this device that is more complicated than you can simulate on a classical computer, but it’s not yet controllable to the precision that you could do the algorithms you know how to do.”
What gives IBM hope is that even an imperfect quantum computer might still be a useful one.
Gambetta and researchers are closing in on an application that Feynman envisioned back in 1981. Chemical reactions and the properties of materials are determined by the interactions between atoms and molecules. Those interactions are governed by quantum phenomena. A quantum computer can—at least in theory—model those in a way a conventional one cannot.
Last year, Gambetta and colleagues at IBM used a seven-qubit machine to simulate the precise structure of beryllium hydride. At just three atoms, it is the most complex molecule ever modelled with a quantum system. Ultimately, researchers might use quantum computers to design more efficient solar cells, more effective drugs, or catalysts that turn sunlight into clean fuels.
Those goals are some way off. But, Gambetta says, it may be possible to get valuable results from an error-prone quantum machine paired with a classical computer.
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