Xanadus X8 photonic quantum computing chip. Credit: Xanadu
Silicon photonics (SiPh), the manufacturing of integrated photonics on the CMOS platform, has been a buzzword for the past two years, given the technology’s promising opportunity to deliver a faster, safer and more efficient solution to data centers increasingly burdened by the ever-growing transfer needs of AI. However, the potential of silicon photonics is not limited to conventional computing and communications.
Xanadu, a quantum computing company founded in 2016 and headquartered in Toronto, Canada, has been building fault-tolerant computers based on silicon photonics chips. Using photons as qubits, Xanadu believes silicon photonics will be the fastest route to achieving a fault-tolerant quantum computer that can operate at room temperature. Zachary Vernon, Xanadu’s Chief Technology Officer in charge of hardware, spoke to DIGITIMES Asia about the opportunities photonics offers to the realm of quantum computing, when he visited Taiwan in November to attend the Asia Pacific Executive Forum 2023 hosted by the Global Semiconductor Alliance.
The race to achieve fault tolerance
Currently, there are several types of quantum computers based on different principles, including superconducting quantum bits, quantum dots, ion traps, and photonics. “Right now, there’s certainly fierce competition between all of them, and you see a lot of approaches that are characterized by the kind of hardware they’re using,” Vernon remarked, noting that because these different approaches are still in the prototype phase, different types of quantum computers are suitable for various short-term problems, and all these short-term problems are little short than real business applications. Ideally, if all approaches to building a quantum computer prove successful, they should all be equivalent and able to solve the same problem, according to Vernon.
“To get to that point, we need to achieve fault tolerance and fault correction, and we think photonics will be the first to get there and the fastest to scale,” the CTO explained, stressing that scaling and performance are both very important to achieve fault tolerance. “You need lots of qubits to encode error correction, but you also need high-performance qubits.”
Photonics allows one to network different chips with optical fiber in different patterns, providing better connectivity than one would typically be able to access in a superconducting approach. As a result of the better connectivity, Vernon indicated, better codes can be accessed, particularly LDPC (quantum low-density parity-check) codes.
“Photonics is really the only approach that can access that, because the other approaches are very limited in the connectivity between their qubits, whereas photonics can use optical fibers to direct qubits wherever you want,” Vernon said. As the number of qubits – now usually measured in the millions – has come to be synonymous with the global quantum race underway, the Xanadu CTO pointed out that photonics will also need millions of qubits to provide an edge. Due to Xanadu’s ability to use better LDPC, it can access ten to a hundred times more logical qubits than competing methods.
“We think it’s very important for anyone working in silicon photonics manufacturing to pay attention to the quantum computing industry,” Vernon emphasized, pointing to the two major advantages of silicon photonics: scalability and room-temperature quantum computing. “All our actual calculations are done in room temperature units.”
Photonics will be the fastest path to scale
According to Xanadu’s projection, once it reaches fault tolerance and starts scaling up to add hundreds of logic qubits per year, Xanadu alone would require hundreds of thousands of 300mm wafers per year, since a quantum computer is like a data center that literally takes thousands or millions of chips to build . “It’s a very significant market opportunity that in a few years will be pretty much directly comparable to the volume of silicon photonics wafers today,” Vernon observed. In the coming years, he said, Xanadu hopes to achieve fault tolerance and scale up to 1,000 error-corrected logic qubits. “It would look like a data center with about 10,000 racks,” he said, indicating that the company’s top priority now is developing the hardware needed to deliver a cloud-distributed, fault-tolerant computer.
In the long term, the use of silicon photonics has the potential to deploy quantum computers closer to the edge. “In principle, there’s no fundamental reason why a quantum computer using photonics can’t be inside a consumer device,” Vernon explained, “there are some technologies that need to be developed for that, but fundamentally that capability is there because they can all work in basically room temperature.” Whether there will be a tool for that application for that, but more time is needed to study what it will look like.
In terms of immediate engagement with customers, Xanadu’s quantum computer programming software library, PennyLane, is the company’s main product offering. Xanadu partnered with Amazon Web Services in its development, in addition to the collaboration with Nvidia. “PennyLane is one of the leading software APIs for developing algorithms for quantum computers,” Vernon noted, “it started out specializing in machine learning applications—quantum machine learning—but a community grew around it to capture a pretty significant of algorithm development market.” The Xanadu CTO also highlighted the hardware-agnostic nature of PennyLane: it’s not limited to photonic quantum computers or our hardware – you can use it on different platforms, and Xanadu has partnered with multiple hardware vendors to make it possible. In one example, Xanadu partnered with several automakers such as Volkswagen that leverage PennyLane to develop quantum algorithms for battery simulation.
The risk of missing out on a global competition
On the cusp of an AI revolution, the Xanadu hardware CTO pointed out that much work has been done in quantum machine learning, although it is still in its infancy. “There’s a lot of algorithmic development going on, and it seems that quantum computers will be able to handle some machine learning tasks in a completely different way,” Vernon said. Nevertheless, large-scale fault-tolerant quantum computers are still needed before one can fully access the implication. “When these things are scaled up to very significant sizes, then it can handle conventional machine learning operations — like matrix operations — more efficiently,” according to Vernon.
Rather than replacing data centers, Vernon believes that quantum computers will augment them, indicating that quantum computers do not address computational problems and applications that are currently done by edge clusters. “The types of algorithms that quantum computing across all approaches addresses are completely different, and they are completely inaccessible to regular classical computers as a result of the mathematical structure of the problems to be solved,” he pointed out, adding that the development of quantum computing is not something incremental which gets a small advantage compared to already existing technology. “A good example is the latest cloud-installed machine we built, Borealis, which was able to beat the world’s most powerful supercomputer – benchmarked against Fugaku – by many orders of magnitude.”
Fundamentally, quantum computing tackles a completely different set of problems that cannot be solved simply by scaling up data centers. “It opens up application markets that are simply out of reach and will always be out of reach with today’s technology,” says Vernon.
Given the strategic importance of quantum computing, a global race has been underway. As for Canada’s advantages in that, the Xanadu CTO observed that the country punches above its weight in the ecosystem, especially in workforce development, and a number of great physicists and engineers coming out of Canadian universities were hired directly by Xanadu. When it comes to Taiwan’s advantage, Vernon believes that Taiwan is the “Mecca of semiconductors” and therefore will also be a hub for silicon photonics one day, thus playing a crucial role in Xanadu’s supply chain in the future. However, he stressed that the Taiwanese ecosystem needs to pay attention to the adaptation and optimization “which would be better sooner rather than later.”
For the photonics ecosystems in Taiwan and elsewhere, Vernon believes that silicon nitride and lithium niobates are two emerging platforms that are extremely important, and Xanadu has been working with them for quite some time. With the help of the Canadian Trade Office in Taipei, Xanadu has built relationships with several foundries and OSATs based in Taiwan, particularly those that have been involved in the manufacturing of Xanadu’s devices. “We believe that Taiwan is perfectly positioned to be a dominant supplier, and what is needed right now is process adaptation and optimization to ensure the compatibility of the silicon photonics processes, both on the manufacturing and packaging side, with the requirements of photonic quantum computing.” Vernon stated.
“There is a risk of missing it if it is not active,” he warned, noting that the US and Europe have made a small advance in photonics quantum computing as they have spent more time and paid more attention to the relevant requirements recently . some years. “The time to act is now to ensure that Taiwan remains competitive, and there is no better place in the world that has the kind of existing infrastructure to support this.”
Zachary Vernon, CTO—Hardware at Xanadu.
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