An interesting article released overnight. It appears IBM may...

An interesting article released overnight. It appears IBM may have solved some of the issue of scaling up to 1121 cubits and possibly beyond.

https://spectrum.ieee.org/ibm-s-quantum-computing-compromise-the-road-to-scale

Quantum computers are some of the most fiendishly complex machines humans have ever built. But exactly how complex you make them has significant impacts on their performance and scalability. Industry leaders, perhaps not surprisingly, sometimes take very different approaches.

Consider IBM. As of this week (8 August), all of Big Blue's quantum processors will use a hexagonal layout that features considerably fewer connections between qubits—the quantum equivalent of bits—than the square layout used in its earlier designs and by competitors Google and Rigetti Computing.

This is the culmination of several years of experimentation with different processor topologies, which describe a device's physical layout and the connections between its qubits. The company's machines have seen a steady decline in the number of connections despite the fact its own measure of progress, which it dubs "quantum volume", gives significant weight to high connectivity.

That's because connectivity comes at a cost, says IBM researcher Paul Nation. Today's quantum processors are error-prone, and the more connections between qubits, the worse the problem gets. Scaling back that connectivity resulted in an exponential reduction in errors, says Nation, which the company thinks will help them scale faster to the much larger processors that will be required to solve real-world problems.

"In the short term it's painful," says Nation. "But the thinking is not what is best today, it's what is best for tomorrow."

IBM first introduced the so-called "heavy-hex" topology last year, and the company has been gradually retiring processors with alternative layouts. After this week, all of the more than 20 processors available on the IBM Cloud will rely on the design. And Nation says heavy hex will be used in all devices outlined in its quantum roadmap, at least up until the 1,121-qubit Condor processor planned for 2023.