Inside the race to build the best quantum computer on Earth: IBM thinks quantum supremacy is not the milestone we should care about.
MIT Technology Review, February 26, 2020
Computing/Quantum computing
By Gideon Lichfield
Google’s most advanced computer isn’t at the company’s headquarters in Mountain View, California, nor anywhere in the febrile sprawl of Silicon Valley. It’s a few hours’ drive south in Santa Barbara, in a flat, soulless office park inhabited mostly by technology firms you’ve never heard of.
An open-plan office holds several dozen desks. There’s an indoor bicycle rack and designated “surfboard parking,” with boards resting on brackets that jut out from the wall. Wide double doors lead into a lab the size of a large classroom. There, amidst computer racks and jumbles of instrumentation, a handful of cylindrical vessels—each a little bigger than an oil drum—hang from vibration-damping rigs like enormous steel pupae.
Rigetti Computing / Justin Fantl
On one of them, the outer vessel has been removed to expose a multi-tiered tangle of steel and brass innards known as “the chandelier.” It’s basically a supercharged refrigerator that gets colder with each layer down. At the bottom, kept in a vacuum a hair’s breadth above absolute zero, is what looks to the naked eye like an ordinary silicon chip. But rather than transistors, it’s etched with tiny superconducting circuits that, at these low temperatures, behave as if they were single atoms obeying the laws of quantum physics. Each one is a quantum bit, or qubit—the basic information–storage unit of a quantum computer.
Late last October, Google announced that one of those chips, called Sycamore, had become the first to demonstrate “quantum supremacy” by performing a task that would be practically impossible on a classical machine. With just 53 qubits, Sycamore had completed a calculation in a few minutes that, according to Google, would have taken the world’s most powerful existing supercomputer, Summit, 10,000 years. Google touted this as a major breakthrough, comparing it to the launch of Sputnik or the first flight by the Wright brothers—the threshold of a new era of machines that would make today’s mightiest computer look like an abacus.
At a press conference in the lab in Santa Barbara, the Google team cheerfully fielded questions from journalists for nearly three hours. But their good humor couldn’t quite mask an underlying tension. Two days earlier, researchers from IBM, Google’s leading rival in quantum computing, had torpedoed its big reveal. They’d published a paper that essentially accused the Googlers of getting their sums wrong. IBM reckoned it would have taken Summit merely days, not millennia, to replicate what Sycamore had done. When asked what he thought of IBM’s result, Hartmut Neven, the head of the Google team, pointedly avoided giving a direct answer.
You could dismiss this as just an academic spat—and in a sense it was. Even if IBM was right, Sycamore had still done the calculation a thousand times faster than Summit would have. And it would likely be only months before Google built a slightly larger quantum machine that proved the point beyond doubt.
IBM’s deeper objection, though, was not that Google’s experiment was less successful than claimed, but that it was a meaningless test in the first place. Unlike most of the quantum computing world, IBM doesn’t think “quantum supremacy” is the technology’s Wright brothers moment; in fact, it doesn’t even believe there will be such a moment.
IBM is instead chasing a very different measure of success, something it calls “quantum advantage.” This isn’t a mere difference of words or even of science, but a philosophical stance with roots in IBM’s history, culture, and ambitions—and, perhaps, the fact that for eight years its revenue and profit have been in almost unremitting decline, while Google and its parent company Alphabet have only seen their numbers grow. This context, and these differing goals, could influence which—if either—comes out ahead in the quantum computing race.
