Quantum-computing corporations have been competing for years to squeeze essentially the most qubits onto a chip. However fabrication and connectivity challenges imply there are limits to this technique. The main target is now shifting to linking a number of quantum processors collectively to construct computer systems massive sufficient to sort out real-world issues.
In January, the Canadian quantum-computing firm Xanadu unveiled what it says is the primary modular quantum pc. Xanadu’s method makes use of photons as qubits—simply considered one of some ways to create the quantum-computing equal of a classical bit. In a paper published that same month in Nature, researchers on the firm outlined how they linked 35 photonic chips and 13 kilometers of optical fiber throughout 4 server racks to create a 12-qubit quantum pc referred to as Aurora. Though there are quantum computers with many extra qubits as we speak, Xanadusays the design demonstrates all the important thing parts for a modular structure that may very well be scaled as much as hundreds of thousands of qubits.
Xanadu isn’t the one firm centered on modularity today. Each IBM and IonQ have began work on linking their quantum processors, with IBM hoping to demonstrate a modular setup later this yr. And a number of other startups are carving out a distinct segment constructing the supporting technologies required for this transition.
Most corporations have lengthy acknowledged that modularity is essential to scaling, says Xanadu CEO Christian Weedbrook, however to this point they’ve prioritized growing the core qubit know-how, which was broadly seen as the larger technical problem.Now that chips with sensible use are in sight and the biggest processors function more than 1,000 qubits, he believes the main target is shifting.
“To get to 1,000,000 qubits, which is when you can begin really fixing buyer issues, you’re not going to have the ability to have all of them on a single chip,” Weedbrook says. “The one solution to actually scale up is thru this modular networking method.”
Xanadu has taken an unorthodox method by specializing in the scalability downside first. One of many greatest benefits of counting on photonics for quantum computing—versus the superconducting qubits utilized by IBM and Google—is that the machines are appropriate with standard networking know-how, which simplifies connectivity.
Nonetheless, Aurora isn’t dependable sufficient for helpful computations because of excessive optical loss; photons are absorbed or scattered as they move by optical parts, introducing errors. Xanadu goals to attenuate these losses over the subsequent two years by developing better components and optimizing structure. The corporate plans to start out building a quantum data center in 2029.
IBM additionally expects to hit a significant modular quantum-computing milestone this yr. The corporate has designed a 462-qubit processor referred to as Flamingo with a built-in quantum communication link. Later this yr, IBM plans to attach three of them to create the biggest quantum pc—modular or not—up to now.
Modularity has all the time been central to IBM’s quantum street map, says Oliver Dial, the chief know-how officer of IBM Quantum. Whereas the corporate has typically led the sphere in packing extra qubits into processors, there are limits to chip dimension. As they develop bigger, wiring up the management electronics turns into more and more difficult, says Dial. Constructing computer systems with smaller, testable, and replaceable parts simplifies manufacturing and upkeep.
Nonetheless, IBM is utilizing superconducting qubits, which function at excessive speeds and are comparatively straightforward to manufacture however are much less network-friendly than different quantum applied sciences. These qubits function at microwave frequencies and so can’t simply interface with optical communications, which required IBM to develop specialised couplers to attach each adjoining chips and extra distant ones.
IBM can be researching quantum transduction, which converts microwave photons into optical frequencies that may be transmitted over fiber optics. However the constancy of present demonstrations is way from what’s required, says Dial, so transduction isn’t on IBM’s official street map but.
IBM plans to attach three of its 462-qubit Quantum Flamingo processors this yr to make what the corporate claims would be the largest quantum pc but.IBM
Trapped-ion and neutral-atom-based qubits work together immediately with photons, making optical networking extra possible. Final October, IonQ demonstrated the power to entangle trapped ions on totally different processors. Photons entangled with ions on every chipjourney by fiber-optic cables and meet at a tool referred to as a Bell-state analyzer, the place the photons are additionally entangled and their mixed state is measured. This causes the ions that the photons have been initially entangled with to turn into linked through a course of referred to as entanglement swapping.
Scaling this as much as hyperlink massive numbers of quantum processors would require numerous work, says John Gamble, senior director of system architecture and efficiency at IonQ. Bell-state analyzers, at present carried out utilizing free-space optical parts, will have to be miniaturized and fabricated utilizing integrated photonics. Moreover, optical fiber is noisy, which means the standard of the entanglement created by these channels is comparatively low. To deal with this, IonQ plans to generate many weakly entangled pairs of qubits and perform operations to distill these right into a smaller variety of higher-quality entanglements. However attaining a excessive sufficient price of high quality entanglements will stay a problem.
The French startup Welinq is addressing this concern by incorporating a quantum memory into its interconnect. CEO Tom Darras says one cause why entanglement over photonic interconnects is so inefficient is that the 2 photons required are sometimes emitted at totally different occasions, so that they “miss” each other and fail to entangle. Including a reminiscence creates a buffer that helps synchronize the photons.
“Whenever you want them to fulfill, they really meet,” says Darras. “These applied sciences allow us to create entanglement quick sufficient in order that it is going to be helpful for distributed computation.”
Useful Modular Quantum Computer systems Want Extra Steps
As soon as a number of processors are linked, the problem shifts to operating quantum algorithms throughout them. That’s why Welinq has additionally developed a quantum compiler, referred to as araQne, that determines the best way to partition an algorithm throughout a number of processors whereas minimizing communication overhead.
Researchers from Oxford University made a recent breakthrough on this front, with the primary convincing demonstration of a quantum algorithm operating throughout two interconnected processors. The researchers carried out logical operations between two trapped-ion qubits on totally different gadgets. The qubits had been entangled utilizing a photonic connection, and the processors executed a really fundamental model of Grover’s search algorithm.
The ultimate piece of the puzzle will likely be determining the best way to adapt error-correction schemes for this new modular future. The startup Nu Quantum just lately demonstrated that distributed quantum error correction shouldn’t be solely possible however environment friendly.
“It is a actually large consequence as a result of, for the primary time, distributed quantum computing and modularity is an actual choice,” says Nu Quantum’s CEO, Carmen Palacios-Berraquero. “Earlier than, we didn’t understand how we’d do it in a fault-tolerant method, if it was environment friendly, or if it was viable.”
This text seems within the March 2025 print concern.
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