This quantum computer built on server racks paves the way to bigger machines

But this work, which the company published last week in Nature, is just a first step toward that vision. Aurora used 35 chips to construct a total of 12 quantum bits, or qubits. Any useful applications of quantum computing proposed to date will require at least thousands of qubits, or possibly a million. By comparison, Google’s quantum computer Willow, which debuted last year, has 105 qubits (all built on a single chip), and IBM’s Condor has 1,121.

Devesh Tiwari, a quantum computing researcher at Northeastern University, describes Xanadu’s progress in an analogy with building a hotel. “They have built a room, and I’m sure they can build multiple rooms,” he says. “But I don’t know if they can build it floor by floor.”

Still, he says, the work is “very promising.” 

Xanadu’s 12 qubits may seem like a paltry number next to IBM’s 1,121, but Tiwari says this doesn’t mean that quantum computers based on photonics are running behind. In his opinion, the number of qubits reflects the amount of investment more than it does the technology’s promise. 

Photonic quantum computers offer several design advantages. The qubits are less sensitive to environmental noise, says Tiwari, which makes it easier to get them to retain information for longer. It is also relatively straightforward to connect photonic quantum computers via conventional fiber optics, because they already use light to encode information. Networking quantum computers together is key to the industry’s vision of a “quantum internet” where different quantum devices talk to each other. Aurora’s servers also don’t need to be kept as cool as superconducting quantum computers, says Weedbrook, so they don’t require as much cryogenic technology. The server racks operate at room temperature, although photon-counting detectors still need to be cryogenically cooled in another room. 

Xanadu is not the only company pursuing photonic quantum computers; others include PsiQuantum in the US and Quandela in France. Other groups are using materials like neutral atoms and ions to construct their quantum systems.