This quantum computer built in server racks paves way for bigger machines

A Canadian startup called Xanadu built a new computer that it claims can be easily scaled to achieve the computing power needed to tackle scientific problems ranging from drug development to more energy-efficient computer learning.

Aurora, a “photonic”quantum computer, crunches numbers by using photonic qubits — information encoded in light. In practice, this involves combining and recombining multiple laser beams using lenses, fibres, and other optical components according to an algorithm. Xanaduโ€™s computer is designed so that the answer it gives to an algorithm corresponds to the number of photons within each laser beam. This is a different approach from that used by Google and IBM which encodes information in the properties of superconducting transistors.

Aurora’s modular design consists of four identical units, each installed into a standard server rack slightly taller and wider than the average person. Christian Weedbrook is the CEO and founder. He says that to make a quantum computer useful, “you have to copy and paste 1,000 of these things, and then network them together.”

Ultimately Xanadu envisions a quantum computer as a specialized server data center consisting of rows and rows of these servers. This is in contrast to the industry’s previous conception of a GPU-like specialized chip inside a supercomputer.

However, this work was published by the company last week. Nature is only a first step towards this vision. Aurora used 35 chips to create a total of twelve quantum bits or qubits. Quantum computing applications that have been proposed so far will require thousands, or even a million qubits. Google’s quantum computing Willow, which was unveiled last year, had 105 qubits, while IBM’s Condor had 1,121.

Devesh Tiwari is a quantum computing research at Northeastern University. He compares Xanadu to building a hotel. He says, “They’ve built a single room and I am sure they can build many more.” “But I donโ€™t know if[they]can build it floor-by-floor.”

He says the work is still “very promising.” According to Tiwari, the number qubits is more a reflection of the investment than the technology’s potential.

The design of photonic quantum computers offers several advantages. Tiwari says that qubits are less sensitive than usual to noises in the environment, making it easier for them to retain information. Photonic quantum computers can be connected via conventional fiber optics because they already encode information with light. The industry’s vision for a “quantum Internet” is to network quantum computers together. This will allow different quantum devices to communicate with each other. Weedbrook says that Aurora’s servers don’t have to be as cool as superconducting computers, so they require less cryogenic technology. The server racks are operated at room temperature. However, photon-counting sensors still need to cryogenically cool in another room.

Xanadu’s not the only company pursuing quantum photonic computers. Others include PsiQuantum and Quandela, both in France and the US. Other groups use materials such as neutral atoms or ions to build their quantum systems.

Tiwari believes that from a technical perspective, no qubit type is going to be “the winner,” but certain qubits are likely to be better for particular applications. Photonic quantum computers are well-suited to Gaussian Boson sampling, a technique that could be used to quickly solve graph problems. “I want more people to look at photonic quantum computer,” he says. He has studied quantum computer with multiple qubit types including photons, superconducting, and other qubits. He is not affiliated with any company. Isaac Kim, a physicist from the University of California Davis, says that Xanadu does not have the error correction capability that many experts believe a quantum computing system will need to perform any useful task. This is because the information stored in a computer quantum is notoriously fragile. Weedbrook says that Xanadu will next work to improve the quality and quantity of photons within the computer. This will make it easier to correct errors. “When you send lasers over a medium – whether it’s chips, fiber optics or free space – not all of the information gets through to the end,” he says. “You’re losing light, and therefore information,” he says. The company is working on reducing this loss to ensure that there are fewer errors.

Xanadu aims at building a quantum datacenter in 2029, with thousands servers containing a billion qubits.

www.aiobserver.co

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