Companies are thinking seriously about how to link quantum processors
Quantum-computing companies have been competing for years to squeeze the most qubits onto a chip. But fabrication and connectivity challenges mean there are limits to this strategy. The focus is now shifting to linking multiple quantum processors together to build computers large enough to tackle real-world problems. In January, the Canadian quantum-computing company Xanadu unveiled what it says is the first modular quantum computer. Xanadu's approach uses photons as qubits—just one of many ways to create the quantum-computing equivalent of a classical bit. In a paper published that same month in Nature, researchers at the company outlined how they connected 35 photonic chips and 13 kilometers of optical fiber across four server racks to create a 12-qubit quantum computer called Aurora. Although there are quantum computers with many more qubits today, Xanadusays the design demonstrates all the key components for a modular architecture that could be scaled up to millions of qubits. Xanadu isn't the only company focused on modularity these days. Both IBM and IonQ have started work on linking their quantum processors, with IBM hoping to demonstrate a modular setup later this year. And several startups are carving out a niche building the supporting technologies required for this transition. Most companies have long acknowledged that modularity is key to scaling, says Xanadu CEO Christian Weedbrook, but so far they have prioritized developing the core qubit technology, which was widely seen as the bigger technical challenge.Now that chips with practical use are in sight and the largest processors feature more than 1,000 qubits, he believes the focus is shifting. "To get to a million qubits, which is when you can start truly solving customer problems, you're not going to be able to have them all on a single chip," Weedbrook says. "The only way to really scale up is through this modular networking approach." Xanadu has taken an unorthodox approach by focusing on…