Google v. IBM, Their Qubits are Different. Which is Better?

Google v. IBM, Their Qubits are Different. Which is Better?

Well worth taking some time to read from the source. Because Quantum is Coming. Qubit.

Inside the race to build the best quantum computer on Earth

Selected notes ~

+  A tale of two transmons

Google’s and IBM’s transmon qubits are almost identical, with one small but potentially crucial difference.

In both Google’s and IBM’s quantum computers, the qubits themselves are controlled by microwave pulses. Tiny fabrication defects mean that no two qubits respond to pulses of exactly the same frequency. There are two solutions to this: vary the frequency of the pulses to find each qubit’s sweet spot, like jiggling a badly cut key in a lock until it opens; or use magnetic fields to “tune” each qubit to the right frequency.

IBM uses the first method; Google uses the second. Each approach has pluses and minuses. Google’s tunable qubits work faster and more precisely, but they’re less stable and require more circuitry. IBM’s fixed-frequency qubits are more stable and simpler, but run more slowly.

From a technical point of view, it’s pretty much a toss-up, at least at this stage. In terms of corporate philosophy, though, it’s the difference between Google and IBM in a nutshell—or rather, in a qubit.

Google chose to be nimble. “In general our philosophy goes a little bit more to higher controllability at the expense of the numbers that people typically look for,” says Hartmut Neven.

IBM, on the other hand, chose reliability. “There’s a huge difference between doing a laboratory experiment and publishing a paper, and putting a system up with, like, 98% reliability where you can run it all the time,” says Dario Gil.

Right now, Google has the edge. As machines get bigger, though, the advantage may flip to IBM. Each qubit is controlled by its own individual wires; a tunable qubit requires one extra wire. Figuring out the wiring for thousands or millions of qubits will be one of the toughest technical challenges the two companies face; IBM says it’s one of the reasons they went with the fixed-­frequency qubit. Martinis, the head of the Google team, says he’s personally spent the past three years trying to find wiring solutions. “It’s such an important problem that I worked on it,” he jokes.

+  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.

+  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.

Source:  MIT Technology Review.  Gideon Lichfield,  Inside the race to build the best quantum computer on Earth…

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